Author Topic: Which Screws Won't Cause Bleed through on Wood Filler For Bookcase  (Read 11119 times)

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Offline bostonmanTopic starter

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Which Screws Won't Cause Bleed through on Wood Filler For Bookcase
« on: September 04, 2023, 03:00:12 pm »
I"m building a bookcase with dados and using Poplar wood (1 and 1/16" thick). I plan to screw the shelves and countersink the screw heads along with filling them with wood putty (?) to cover the holes and then clear stain.

I'm uncertain which screws to use. Not necessarily because of wood splitting or anything (I plan to pre-drill the holes to minimize the risk of cracking and/or screws stripping), but more about whether the material from a screw will bleed through over time.

The only screws I have are the yellow Deckmate (construction ?) from Home Depot which I planned to use, but concern on whether that finish will breakdown over time bleeding through the stain.

Does anyone have recommendations?

« Last Edit: September 25, 2023, 01:22:10 am by bostonman »
 

Offline David Hess

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #1 on: September 04, 2023, 03:37:08 pm »
I like the GRK screws which are available from Home Depot because they are rated for structural loads and use Torx drive, but they also come in a finishing trim head version.  They are plated/coated to prevent bleed through, but the sure solution is to use stainless steel screws.
 

Offline PlainName

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #2 on: September 04, 2023, 03:57:03 pm »
If this is indoors, is there any real problem with type of screw so long as it's strong enough? Extremely unlikely to corrode, particularly since you'll be sealing it in.

When I built my office I just used whatever was a good price at Screwfix (kind of UK Home Depot in a loose way). Twenty years later nothing has fallen apart, and when I do look at the original screws they look just like they did then. OTOH, same screws outside and you know they've seen weather, so they're not particularly anti-corrosion.
 

Offline I wanted a rude username

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #3 on: September 04, 2023, 04:01:17 pm »
The surface finish itself is not a concern, corrosion of the bulk steel of the screw is. This shouldn't be a problem for bookcases since they must never get wet. But it could happen.

They type of surface finish is often less important than how well it's performed. Chrome and zinc are both pretty good for dry environments but in adverse environments I've seen separate examples of both chrome and zinc coated parts be either really resistant (basically no rust ever) and also extremely rust-prone.

Your best option might be either to find screws that actually have some kind of salt spray resistance rating, or stainless as David Hess suggests (and then you also want a rating because some "stainless" just isn't). You also won't need to cover them with putty, as they'll look good exposed.

Also consider the psychological perspective: if you're building a once-off, it's nice to use high quality components because then every time you look at it you'll be reminded of how good it is.
 

Online Ian.M

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #4 on: September 04, 2023, 04:09:08 pm »
Don't  cover them with putty/filler - that's just fugly under a clear finish.  If you want to do this properly, get a plug cutter set and cover them with cross-grain plugs cut from the same wood as the rest of the bookcase, with the grain aligned.
 
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Online themadhippy

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #5 on: September 04, 2023, 04:56:27 pm »
dab of rust proof primer on the screw head if your really worried
Quote
Don't  cover them with putty/filler - that's just fugly under a clear finish
cheapskate method is to mix the sawdust youve gained from all the cutting and drilling with a bit of wood glue,If you use a clear glue like cascamite its almost invisable
 

Online Benta

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #6 on: September 04, 2023, 08:09:06 pm »
And the pro way is to use dowels and glue.
No reason for filler, it's invisible when done correctly. Not really possible to do with a hand drill, you need a drill press plus additional tooling.

« Last Edit: September 04, 2023, 08:10:41 pm by Benta »
 
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Online TimFox

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #7 on: September 04, 2023, 08:44:12 pm »
Dowels and glue greatly increase the strength of the joint.
A Japanese "nokogiri" handsaw is ideal for cutting the dowel after hammering in place:  sometimes the result does not even need sanding to be flush.
However, a recessed screw (head covered by a wood plug) helps to hold the two pieces together, relieving shear on the glue.
 
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Offline Gyro

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #8 on: September 04, 2023, 08:46:02 pm »
The other method is to use pocket screws, with associated jig. These are invisible from the outside, the screws going outwards at an angle through the bottom surface of the shelves through neat oval 'pockets'. The screws are a specific type, taking that decision off your hands.  I can't say I'm a great fan, but they seem to be the modern thing.

eg:  https://www.familyhandyman.com/project/how-to-use-pocket-screws/
Best Regards, Chris
 
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Online T3sl4co1l

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #9 on: September 04, 2023, 08:46:05 pm »
Drywall screws are fine.

Tim
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Online TimFox

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #10 on: September 04, 2023, 09:13:37 pm »
Specifically for bookcases, when loaded, I have found that there are substantial forces tending to push the verticals outwards, stressing whatever demountable fittings, screws, dowels, or biscuits are used to hold the horizontal shelves in place.
Dowels are good for fighting the vertical forces, and screws are good for fighting the horizontal forces;  choose a good combination.
For my constructions, I use flat-head screws (I prefer Robertson square-drive heads) with wood plugs over them and glued dowels between the screws:  the plug and dowel diameters match and cannot be distinguished externally.
« Last Edit: September 04, 2023, 09:16:25 pm by TimFox »
 

Offline jpanhalt

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #11 on: September 04, 2023, 09:53:53 pm »
In 1970, I built a large bookcase with 3/4 inch veneer core birch plywood.  Shelves were also 3/4 and were supported on adjustable standards dadoed into the sides and verticals.  It was approximately 84" tall x approximately 120" wide (4 columns, 30" wide).  The standards were attached with  ordinary FH wood screws short enough not to penetrate the sides and verticals.  It has been packed with books and survived more than 50 years.  One thing I discovered is  not to exceed 30" width for a shelf less than 10" deep.  If you want deeper, increase the thickness.
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #12 on: September 05, 2023, 01:32:06 am »
I looked into pocket screws and various options.

My main question/concern was which screw(s) can possibly bleed through wood fill (I am aware pegs may be a better option).

I'll figure out which option I'll go with, but I have already bought wood fill, but, as I said, it was a question more about bleeding through than options. Also, this bookcase will be suspended with threaded rod. The dados are more for look since the rods will support the shelves.

The wood (as mentioned) is Poplar, 1 and 1/16" thick, 11.25" deep, approx. 48" wide, 12" between each shelf , five shelves (six if you count the top which will be against the ceiling), and a computer model (done by a former mechanical engineer co-worker) shows that the threaded rod should be placed approx. 12" from the edges for ideal support (at least that's what I believe is the distance based on the study he did - see attached - it's been a few years since I went over this with him).

Without including the weight of the wood, I currently have about 300lbs of books. Some math helped by the former mechanical engineer at work showed that x2 5/16" (one on each end) should be more than enough to support triple my needs; and I may go with 3/8" or 7/16".

 

Offline David Hess

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #13 on: September 05, 2023, 04:19:08 am »
Drywall screws are fine.

I stopped using drywall screws after having some break, and they are the worst for rusting and bleeding through.  Unlike construction screws, they are not specified for live loads.  I suspect the problem is that they are not heat treated to prevent work hardening, but maybe it is just a problem with cheap material selection.

One thing I discovered is  not to exceed 30" width for a shelf less than 10" deep.  If you want deeper, increase the thickness.

It is not as pretty, but a strip can be added along the edge underneath a thin shelf to strengthen it preventing sagging under load.
 

Offline jpanhalt

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #14 on: September 05, 2023, 08:42:48 am »
Even with 1-1/16" poplar, a 48" wide shelf may sag, particularly if loaded with heavy books (e.g., 10" deep).

I used standards and clips to get adjustable shelves.  I would probably not do that again, as once set up, we rarely if ever adjusted them.  It was generally more appealing to have the shelves line up across the face.*  Thus, rather than end screw the shelves from the outside, I would use cleats on the inside.  That allows shelves to be removable with no hardware showing.  If you want a more rustic look, I would not use a wood fill, but rather use either domed wood plugs or dowels  cut flush and sanded.  Dowels cut and sanded are considered by some to be an additional artistic touch.

*A curio cabinet I built, on the other hand, was intentionally designed with short shelves at multiple levels and not lined up side to side.  The purpose was different.  A bookshelf to me is functional over appearance.
 

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #15 on: September 05, 2023, 12:42:08 pm »
Drywall screws are fine.

I stopped using drywall screws after having some break, and they are the worst for rusting and bleeding through.  Unlike construction screws, they are not specified for live loads.  I suspect the problem is that they are not heat treated to prevent work hardening, but maybe it is just a problem with cheap material selection.

IIRC, they're somewhere around 1045 steel, which doesn't really harden, but still hard enough that it tends to snap rather than bend.  They're good for some strength, but to be fair I should've said deck screws -- or I suppose that includes the "construction" kind -- essentially same style, but made for it, properly tempered (hm, I don't know what alloys, actually), and coatings to reduce friction and corrosion.

Main thing is, just avoid those traditional/old style tapered screws: mild steel, huge friction, half of them strip out before even getting flush, even with pilot holes.  Man I hate those things...


Quote
It is not as pretty, but a strip can be added along the edge underneath a thin shelf to strengthen it preventing sagging under load.

Yep, greatly saves on material.  The sides are braced by the shelves so don't need much any stiffening, but the shelves themselves benefit from a flange or beam along them.  Doesn't have to be at the front (though, that may be the most convenient mounting place), and doesn't have to be wood either -- indeed, if you need to save vertical height, or weight, consider an exceptionally stiff material (in comparison), like steel!  Just mount it in such a way to avoid expansion issues -- drill slotted holes for example.  Hot-rolled flat (mounted flush to the face) or angle (mounted face or underneath) would do well, and has a soft corner safe for touching; it might be worth sanding and varnishing/painting before assembly to get a more pleasant finish.

Even aluminum is a great improvement, though you need more of it (although, less by overall weight, if you can afford the increased vertical space).

Tim
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Offline PlainName

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #16 on: September 05, 2023, 01:00:57 pm »
In one instance I solved the problem of long shelves by putting a fake vertical leg in the middle (both length and widthways) :)

It was actually just several sections (to avoid making holes in the shelves) so the top shelf pushed on the next one down, all the way to the floor. Sounds terrible but actually useful as bookends. I suppose, if some equipment instead of books were on there, each support could be moved over a bit to give space, but it would spoil the effect of a square post exactly fitting square holes through all the shelves :)
 

Offline madires

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #17 on: September 05, 2023, 01:44:58 pm »
You can get special wood construction screws, e.g. SPAX, plus covers (plastic caps).
 

Offline David Hess

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #18 on: September 05, 2023, 02:25:10 pm »
Drywall screws are fine.

I stopped using drywall screws after having some break, and they are the worst for rusting and bleeding through.  Unlike construction screws, they are not specified for live loads.  I suspect the problem is that they are not heat treated to prevent work hardening, but maybe it is just a problem with cheap material selection.

IIRC, they're somewhere around 1045 steel, which doesn't really harden, but still hard enough that it tends to snap rather than bend.  They're good for some strength, but to be fair I should've said deck screws -- or I suppose that includes the "construction" kind -- essentially same style, but made for it, properly tempered (hm, I don't know what alloys, actually), ...

I was looking for non-Philips/slotted drive construction screws for use in an overhead safety application (1), and what originally caught my eye is that GRK provides bending, shear, and tensile strength in their datasheets.  They also make the same screws in with finishing trim heads and stainless.

Quote
Quote
It is not as pretty, but a strip can be added along the edge underneath a thin shelf to strengthen it preventing sagging under load.

Yep, greatly saves on material.  The sides are braced by the shelves so don't need much any stiffening, but the shelves themselves benefit from a flange or beam along them.  Doesn't have to be at the front (though, that may be the most convenient mounting place), and doesn't have to be wood either -- indeed, if you need to save vertical height, or weight, consider an exceptionally stiff material (in comparison), like steel!  Just mount it in such a way to avoid expansion issues -- drill slotted holes for example.  Hot-rolled flat (mounted flush to the face) or angle (mounted face or underneath) would do well, and has a soft corner safe for touching; it might be worth sanding and varnishing/painting before assembly to get a more pleasant finish.

An I-beam type of construction would be ideal for saving weight, but I settle for something like a 1x2 wooden strip along the bottom of the front edge so that it does not take up too much vertical space.  It would work better if set back slightly, but I prefer for it to be fully visible.  I am sure you know this, but for others, moving the edge of the strip further away from the center of bending places more strain on it so more force is applied to restore the bending, so extra thickness has more effect than extra width, which is why i-beams use that shape.

(1) A wooden stairway collapsed under me because it was held in place with only friction from overhead *nails*.  WTF!  Yea, government building inspectors and permits are about safety.  *rolls eyes*
« Last Edit: September 06, 2023, 07:51:33 pm by David Hess »
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #19 on: September 06, 2023, 04:45:34 pm »
From reading the replies, it looks like the yellow Deckmate screws could bleed through over time.

I'm better of with stainless steel then?
 

Online Ian.M

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #20 on: September 06, 2023, 05:31:43 pm »
Poplar is one of the preferred woods for sword sheaths because it doesn't have high enough tannic acid levels to corrode steel in a reasonably dry environment.  Therefore I think that unless you live in a tropical swamp, it is highly unlikely  that even uncoated plain steel screws will cause significant discoloration round them for more decades than any of us are likely to care about.   However, dip the screws in boiled linseed oil or varnish and drive them wet, and they will be significantly protected against corrosion, drive easier and hold better.

The highest risk of staining is from the plastics and resins in modern wood fillers degrading . . .
 
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Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #21 on: September 06, 2023, 07:02:07 pm »
Quote
The highest risk of staining is from the plastics and resins in modern wood fillers degrading

Ironically, wood fill is most likely the way I'm going. I know it may not be the prettiest, but it's the direction I'm planning to go.

My initial concern was whether the chemicals on the screws would begin deteriorating into the wood fill and then be exposed. Seems like maybe I don't need to worry as much as I do the wood fill.
 

Offline AndyBeez

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #22 on: September 06, 2023, 07:21:19 pm »
You can make a 'cheat filler' by mixing PVA wood glue with dust from the wood you are filling. Simply collect up the wood sandings. At a glance the color match can be pretty good. PVA is also reasonably inert to metal fixings if kept dry.
 

Offline jpanhalt

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #23 on: September 06, 2023, 07:23:59 pm »
I still don't see why you want a plastic wood filler rather than dowels sanded flush.  Look at any fender bender repaired with "Bondo" vs. old fashioned, skillful bumping and just a little lead 10 years later.  The plastic always shows.

End screws in the shelves will be strong enough, but your bookcase cannot be taken apart for moving.  In other words, it will become a fixture in the house.  Why not build it on the wall?
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #24 on: September 07, 2023, 01:37:26 am »
Quote
Why not build it on the wall?

Without increasing support, I wouldn't trust the wall beams.
 

Online MarkF

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #25 on: September 07, 2023, 02:40:50 am »
No screws.

Dado slots and wood glue.
I've built many bookcases and tables.  They are basically made of 3/4" boards (some with plywood tops in my workshop).
It's all joinery and glue.  The glue holds it together.  Not the screws.

I have 4 bookcases and 3 tables that are over 20 years old without any issues.  I used a few brads and clamps to hold them together while the glue dries.  The one table has a heavy band-saw sitting on it and none of the joints have come apart in all these years.

You should not be relying on screws or nails to hold your woodwork together.
 
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Offline jpanhalt

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #26 on: September 07, 2023, 10:19:49 am »
I agree on the dado (or cleat).  A quick search revealed some opinions (stackexchange):

https://woodworking.stackexchange.com/questions/10995/nails-plus-glue-into-endgrain-vs-screws-plus-glue-vs-dado-for-shelf
https://woodworking.stackexchange.com/questions/7898/endgrain-screw-withdrawal-force

Pocket screws in the shelf bottoms might be an option that would not require any filler.  A small dado (1/4" deep or less), glue, and pocket screws for fixturing should be quite strong.  I suspect a shallow dado with your end-grain screws would allow easier alignment than simply using end-grain screws in a butt joint.  Dados are made on a presumably square machine, while end-grain screwing would depend on proper drilling of a pilot hole and carefully driving the screw perpendicular or robust clamping.

I have used poplar mostly for patterns and not for finished pieces.  (One exception was the bottom rail on a garage door that was 2" thick.)  Does 3/4"  poplar cup as badly as softer woods?  If cupping is anticipated, dados or cleats would provide better resistance.
 

Offline David Hess

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #27 on: September 09, 2023, 02:14:10 am »
No screws.

...

It's all joinery and glue.  The glue holds it together.  Not the screws.

...

You should not be relying on screws or nails to hold your woodwork together.

Good glued joints are stronger than the wood.

I recently repaired an old hardwood desk which was coming apart after rough handling during a move.  The only structural nail joints were in sheer, but it had that old dark brown glue (hide glue?) for the rest and it had completely failed.  I replaced the nails with GRK finishing screws and clamped the whole thing together with Tightbond after cleaning the joints with water and sandpaper.
 

Offline CatalinaWOW

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #28 on: September 09, 2023, 03:21:47 am »
I'll pile on for dado joints with glue, with screws just to hold things together while it dries.  The screws aren't absolutely necessary, but they are far cheaper than buying enough clamps to do the job, and make the project ready for the next assembly step immediately.

I have never had a problem with screws staining the wood in an indoor environment, but it is quite common in outdoor environments. If you live in a highly humid location and the environment for the shelves is not conditioned it is conceivable that the screws will do some staining.  Brass generally doesn't, same with stainless steel.  The coated construction screws are resistant to staining, but given enough moisture and minor dings to the coating during transportation and installation they aren't absolutely stainproof.  Dry wall screws are among the worst for staining, and I have even seen stains from the moisture in paint on rare occasions.

The old hide glues do fail after enough time, moisture and rough handling.  I think the modern glues hold up better, but don't really have any experience with 50 or more year old joints with the new glues which is about as young as any hide glue joint is going to be.  I do have experience with them up to 40 years and if not used in wet locations they do fine.  But I suspect 50 years will satisfy your needs.  Some of the new glues are rated for outdoor use, but can report that they don't hold up to extreme wet environments.
 

Online T3sl4co1l

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #29 on: September 09, 2023, 04:35:41 am »
Good glued joints are stronger than the wood.

I recently repaired an old hardwood desk which was coming apart after rough handling during a move.  The only structural nail joints were in sheer, but it had that old dark brown glue (hide glue?) for the rest and it had completely failed.  I replaced the nails with GRK finishing screws and clamped the whole thing together with Tightbond after cleaning the joints with water and sandpaper.

Mattias Wendel recently (well, maybe it's closer to last year by now; or previous years for that matter!?) did a whole bunch of measurements on various styles of joints (butt, lap, tenon, box, pinned, screwed, etc.), including several glues, and found comparable results.  Mind, not all the joints failed at the wood rather than the glue -- most did fail at the glue, and this was relatively soft material (white pine) I think?? (or maybe it was including maple as well, I forget; look up the videos, they're great!*), but it's close enough that you don't really mind.

Or if you don't mind utterly overkilling it, there's always epoxy. :^)

*I can think of, basically just a few complaints with methodology/analysis, IIRC; which leaves quite a lot of useful results and conclusions.

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Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #30 on: September 12, 2023, 02:22:14 am »
I meant to ask, did anyone understand the stress analysis I posted in Reply #12?

Someone did that for me a while back. It shows how the wood will bend based on varying the location of the threaded rods. Unfortunately the mechanical engineer performed the analysis for me, but then he left and I left.

I understand the visual, but I don't grasp which location is the "ideal" distance between rods.
 

Online T3sl4co1l

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #31 on: September 12, 2023, 03:11:19 am »
You mean this? https://www.eevblog.com/forum/mechanical-engineering/which-screws-are-safe-for-building-a-bookcase/?action=dlattach;attach=1866340

Well, the displacement decreases as separation decreases, but I don't see what loading is. Or, is it just the arrows? What about weight on the ends, or in front / behind the mounts?

The poles will tilt/twist a bit too, and it's not clear if those were modeled as rigid points, or material with some flex itself.  For sure they will not hold the support points level.

Flex is easy enough to understand from moments.  The further away a force is applied from a support point, the greater its torque against the support.  For a given load anywhere on a uniform beam with two support points, the ideal positions are 1/4 and 3/4 since any point is at most 1/4 the beam length away from a support.

Exact values change whether the mounts are rigid, when higher dimensions are included (i.e. the shelf is a sheet moreso than a beam), etc., but that's a quick starter.

Tim
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Offline CatalinaWOW

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #32 on: September 12, 2023, 05:20:17 am »
You mean this? https://www.eevblog.com/forum/mechanical-engineering/which-screws-are-safe-for-building-a-bookcase/?action=dlattach;attach=1866340

Well, the displacement decreases as separation decreases, but I don't see what loading is. Or, is it just the arrows? What about weight on the ends, or in front / behind the mounts?

The poles will tilt/twist a bit too, and it's not clear if those were modeled as rigid points, or material with some flex itself.  For sure they will not hold the support points level.

Flex is easy enough to understand from moments.  The further away a force is applied from a support point, the greater its torque against the support.  For a given load anywhere on a uniform beam with two support points, the ideal positions are 1/4 and 3/4 since any point is at most 1/4 the beam length away from a support.

Exact values change whether the mounts are rigid, when higher dimensions are included (i.e. the shelf is a sheet moreso than a beam), etc., but that's a quick starter.

Tim

I know you know this Tim, but to clarify for others, the 1/4 and 3/4 positions are ideal for a uniformly loaded beam.  And it isn't a bad approximation for a bookshelf since books are somewhat uniform in weight.  But if you have ten copies of the CRC Handbook of Chemistry and Physics, it would be worthwhile to spread them out along the shelf.

The usual practical approach to all this is to make the shelf much stiffer and stronger than is absolutely necessary per the structural analysis.  That way the accuracy of the assumptions about loading, joints and material properties of the shelf are not critical.  It also allows you to put the support rods where the house structure demands and even adjust them for practical reasons.  For example it is convenient to have the rods at the end of the shelves where they can double as bookends, and where they don't interrupt putting books on the shelf.  Not ideal structurally, but these shelves aren't being launched into space so a little extra beef isn't the end of the world.

If you look at the equations for beam deflection it is immediately obvious why adding a lip on the shelf is such a powerful way to improve shelf performance.  Even greater results come from putting a back (even of something really weak like pressboard) across the back of the shelves.  It has the added benefit of keeping books from being pushed off the back.  May not satisfy the aesthetic goals, but that is where the engineer and artist in your soul have to do battle to come up with a final solution.  A compromise that some find appealing is a tensioning cable under the shelf, combined with a riser similar to the bridge on a stringed instrument.
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #33 on: September 12, 2023, 03:50:21 pm »
Without a vertical beam of some sort down the middle of all the shelves, I'd assume nothing is going to keep the shelves from bending.

The analysis the guy did (I believe) is based on a load, and believe he was using 500lbs as a "safe" assumption (not including wood weight).

The analysis is helpful, but I didn't see which rod spacing was ideal. All the analysis showed was deflection at different points for rod distancing.

Without looking, from what I remember, I have approximately 240lbs of books (some are thick text books like physics, calculus, etc... and others are much smaller). The weight of the Poplar wood I haven't done yet, but it will be 1-1/16" thick wood, 48" wide shelves, slightly under 12" spacing between shelves, 11-1/4" depth, six shelves (including the one across the top that will be against the ceiling), and the two sides.

I'm over estimating at the moment, and saying the weight of wood for each shelf is 50lbs (totaling 300lbs), and each side is 100lbs, so wood weight total is 500lbs. Add that to my current books and that's 740lbs.

He did a calculation for me and I think 5/16" stainless steel threaded rod (one on each side) would hold triple that after even after using 50% reliability number from the maximum 70,000psi load that the rod specification has.

My personal preference is to go with 3/8" (or even maybe 7/16") rod, and, from what I can estimate on the load stress analysis, place the rods 12" from the sides for the best deflection reduction. The sides have a dado, so the shelves won't tilt forward to back, and shelf bending is just the nature of anything horizontal.

 

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #34 on: September 13, 2023, 05:13:17 am »
Without a vertical beam of some sort down the middle of all the shelves, I'd assume nothing is going to keep the shelves from bending.

Well it will ALWAYS bend -- as it must.  You can only reduce the bending arbitrarily; well, not even arbitrarily, really, because even if you make it out of carbide, or diamond, I mean, you can't go up from there, once it's solid material of the highest modulus, that's all you can do, no matter the price.

But needless to say, in practical terms, using stiffer materials (steel > aluminum > wood > plastic) and stiffer designs (solid plate of given thickness vs. ribbed/trussed beams of given height vs. plate of much less height) gets deflection down to reasonable values (say, imperceptible deflection; <0.1% would be alright).


The ratios of stiffness dictate how much load is shared between shelf and pole, and also of course load distribution and shelf shape.  I get the feeling, steel rod isn't quite stiff enough to break at any achievable strain rate versus that kind of load, with panels that thick, but thicker obviously will hold more.  Yeah, 5/16 or 3/8 feels about right.

Note that it needs to transfer that load /somewhere/; if you have a big fat beam across the top, that'll do something.  Otherwise it's just chaining shelves together (I guess??) which doesn't mean anything if all are evenly loaded.  And the value proposition is then, saving on shelf thickness, trading it for that beam instead.  If you're just doing shelves and nothing else, the rod only does something when some shelves aren't loaded.

Or if it's at an angle to transfer load to the sides, that would be something, but not very convenient for actually using the shelves obviously. :P

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Online MarkF

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #35 on: September 13, 2023, 05:36:36 am »
The bookcases I've made are out of 1"x12" pine boards and a width between 30" to 36".
There is also a 1/4" plywood back which is glued to the sides and each shelf.
Also, the shelves are spaced approx 14" in height.

If the shelves are movable, you will of course need a wood strip (1.5" to 2" wide) glued to the front and back edges of each to keep them from bending.



I have not had any problems with the shelves sagging/bending.  I don't see any need for metal rods.
I also have some half height bookcases (made the same way that are 4 ft wide).  Each shelf is completely filled with magazines.  There are no bending problems but I would not recommend making 4 ft wide bookcases.
« Last Edit: September 13, 2023, 05:45:48 am by MarkF »
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #36 on: September 13, 2023, 12:09:11 pm »
The rods (as mentioned) are to suspend the bookcase.

I plan to place a beam across my attic joists and suspend the bookcase with the threaded rod.

Per my original post, I believe stainless screws are the best option to avoid bleeding through the wood filler. I looked into pegs to cover the screw holes on the side of the bookcase, but the grain and color doesn't match the stuff I have. Some of the Poplar I have has dark grains and some light green I believe. In any case, I think the original post can be considered closed because going with deck screws may cause the chemicals to bleed whereas stainless steel screws are the best option.

As for threaded rod displacement, does the 12" from that analysis document look correct? I'm uncertain what the document is telling me except how the shelves bend based on rod positioning, but looked liked 12" from the sides was the best choice.
 

Offline PlainName

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #37 on: September 13, 2023, 01:08:49 pm »
Quote
The rods (as mentioned) are to suspend the bookcase.

I plan to place a beam across my attic joists and suspend the bookcase with the threaded rod.

Ah! That's a very different thing to what everyone is imagining. Could be quite cool :)

In that case I would go for the horizontal strip for strengthening. It would usually go underneath at the back,  but in your case I think it would be dual-purpose to have it on the top side - it will stop (or vastly reduce) the shelves bending and also prevent the books falling off the back. Use the support rods as bookends.
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #38 on: September 13, 2023, 02:47:48 pm »
Well, in my defense, this thread deviated quite a bit.

I'll admit, I didn't make the subject line read quite clearly as my question intended. It was meant to start off as questioning materials and chemicals of screw heads and whether using Deckmate (i.e. the yellow screws) would bleed through wood fill.

As with any project and engineers, many provided great feedback and alternatives. I further deviated by asking about rod positioning based on the analysis I attached.

Before I drill holes in the shelves (plans are to do so this weekend), I want to understand the best location. So far I think the 12" from the analysis is the best, but I'm somewhat guessing on the deflection based on looking at the physical bending photos of each different location.

As for screws, as I've mentioned, I think stainless steel (the screws to hold the shelves in the dados onto the sides of the bookcase, not the vertical threaded rod going through each shelf - although that will be stainless steel too) are my best choice to avoid bleeding.

Just to elaborate, the three things I'm confirming: stainless steel screws for the bookcase sides are my best choice, 5/16" stainless steel threaded rod (one on each side) will be an adequate diameter to hold (over estimating) 1200lbs total weight including wood (although I may actually go with 3/8" threaded rod or possibly 7/16"), and is 12" from each side the best deflection point to drill holes for the threaded rode?
 

Online Ian.M

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #39 on: September 13, 2023, 03:30:25 pm »
Stainless threaded parts are extremely high risk for galling.  There's no way I would risk running multiple stainless nuts an average of half the length of a couple of yards of stainless allthread.  It only takes ONE seized nut while getting them into rough position to wreck the rod so badly you'll have to cut it up to remove it, and start over.

You've got three alternatives here - bronze nuts wont gall on a stainless thread, or turn the thread off the rod in a lathe, except for 1" below each shelf position, and use plenty of copper antiseize to reduce the risk of galling when spinning the nuts over each 1" threaded section.  Of course  that has its own problems around woodwork - cleanup wont be fun!  The third alternative is *NOT* to use stainless.  Galling of bright zinc plated steel nuts and allthread is minimal if kept lubricated during assembly. However, you've then got to keep it dry or you will have a high risk of rust staining.
« Last Edit: September 13, 2023, 03:51:30 pm by Ian.M »
 

Offline jpanhalt

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #40 on: September 13, 2023, 03:39:55 pm »
How do you plan to attach the threaded rod to the cable? 

Amazon has stainless lifting eyebolts with female threads (attached).  Those in the picture are 8mm and 10mm.  I suspect SAE threads in the 3/8" size will be easier to find than smaller ones.  I suggest swagged loops for the cable, but I have seen some that clamp the cable.  Metric threaded rod from Zoro is reasonably priced.  I just got some about a month ago.

EDIT: Stainless is probably not needed.  Black iron is pretty popular for home interior use.
« Last Edit: September 13, 2023, 03:42:39 pm by jpanhalt »
 

Online T3sl4co1l

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #41 on: September 13, 2023, 04:44:42 pm »
Ahh, rafters, that explains that.

Yeah, you might want to use galvanized rod instead of stainless; or galvanized nuts on it, perhaps.  The risk of that bleeding is less than the almost-certain bleeding of liberally-smeared anti-seize...

Note that you can always put in more rods, and probably should, unless you have some other means of controlling sway and twist.  Just two rods hanging down, say, even a few feet, sounds like a wobbly mess, especially when loaded.

Oh also, so the total load is carried on the rods, that explains that, and I would much prefer thicker rod in that case, maybe even a few 1/2" rods.

Mind that rafters don't carry much torsion, which will be front-to-back sway.  Maybe that's what the cables are for; I seem to have skimmed over their mention.  Diagonal bracing to nearby rafters would be more effective (variably cables go slack then twang, slightly better to avoid the nonlinearity), and that can be just ordinary angle iron or whatever.

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Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #42 on: September 13, 2023, 05:56:42 pm »
No cables, not sure how that got brought up.

The beam across the attic joists will be laid across about four or five joists. These joists rest directly on the load bearing wall, so the weight is transferred to the basement columns.

I considered front to back and side-to-side sway, but will screw the bottom of the case into the wall. Not much force is needed, so two screws (one on each side) will be more than enough (I can always put more screws if needed).

This way the 2x4's in the wall will not have any load on them, they'll just hold the bookcase from swaying. All the vertical weight will be on the rod.

Attached are two rough drawings to (hopefully) clear any confusion.
 

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #43 on: September 13, 2023, 06:08:54 pm »
Ah, that solves twist too.  Probably make the wall anchor screws in slots so they don't try to bear weight, that should do it?

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Offline wraper

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #44 on: September 13, 2023, 06:13:20 pm »
The only screws I have are the yellow Deckmate
Yellow screws are a better type of zinc plated. Basically the best corrosion resistant screws after stainless steel.
 

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #45 on: September 13, 2023, 06:14:57 pm »
instead of a beam have you considered  unistrut and  zebadees
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #46 on: September 13, 2023, 06:30:22 pm »
Quote
Probably make the wall anchor screws in slots so they don't try to bear weight, that should do it?

Exactly. If any expansion or sagging takes place, the screws in the wall will be safe.

Quote
instead of a beam have you considered  unistrut and  zebadees

I planned to use unistrut instead. It's a small detail, I posted the pictures JUST for a visual on what I'm talking about. Also, what is Zebadees?

Unfortunately I think this thread has gone off the deep end as I should have just asked whether Deckmate yellow screws will bleed through wood fill. Maybe I shoudln't have mentioned the bookcase portion of the project. :)
 

Online themadhippy

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #47 on: September 13, 2023, 07:05:47 pm »
Quote
Also, what is Zebadees?
What we call the spring nuts,after a popular 70's cartoon character

 

Offline djsb

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #48 on: September 13, 2023, 07:10:16 pm »
Are there any references that cover the traditional construction of bookcases and shelving for use in the home? The only thing that I've ever made is a pair of transmission line loudspeakers using 18mm thick MDF. I did a bit of in secondary school, but that was a LONG time ago. Thanks.
David
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Offline Gyro

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #49 on: September 13, 2023, 07:15:00 pm »
Quote
Also, what is Zebadees?
What we call the spring nuts,after a popular 70's cartoon character

Yay, The Magic Roundabout, bring back Dylan!  :D  (not forgetting Florence and Dougal obviously)
.
https://en.wikipedia.org/wiki/The_Magic_Roundabout
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Offline CatalinaWOW

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #50 on: September 14, 2023, 12:16:46 am »

Just to elaborate, the three things I'm confirming: stainless steel screws for the bookcase sides are my best choice, 5/16" stainless steel threaded rod (one on each side) will be an adequate diameter to hold (over estimating) 1200lbs total weight including wood (although I may actually go with 3/8" threaded rod or possibly 7/16"), and is 12" from each side the best deflection point to drill holes for the threaded rode?

You are both over and underthinking this.  But to your questions.

 Stainless steel screws are fine, though I think you would have not problems with several of the other types mentioned on this thread.  There are many grades of stainless steel, but the lowest strength stainless steel threaded rod carried by McMaster Carr has a yield strength of 70,000 psi.  Assuming UNC (coarse thread 5/16) which will have lower cross section area than a UNF rod that strength computes to 3500 lbs per rod.  More than enough.  What you buy at the local home center is unlikely to be meaningfully worse relative to your loads.  You can deal with the galling with lube or appropriate nuts (galling is also less likely when the nuts are not loaded.)  Do be sure to spread the load with washers, preferably fender washers.  I would be more worried about nuts pulling through wood than about the rods failing.   I wouldn't worry too much about the ideal placement of the rods.  You are fixing the ends with the dado joints creating something that is something sort of like a fixed joint, and distribution of the loads left and right and between shelves will depend on the exact way you adjust the supporting nuts, and will be further adjusted by how the wood moves with temperature and humidity.  If you like the looks of the spacing you have chosen it will work well enough and there isn't any analysis that won't be made wrong by the details of your installation. 

Attaching the shelves to the wall is a good idea (and even would be required by building codes in some locations), but further complicates the load distribution.  Ideally the attachment would allow free motion in the vertical direction and none in the other two.  Hard to do in practice so you will have to live with what you can make, and it will share the loads further complicating the analysis.  The simplest way to make the attachment is with L-brackets at the rear of one or more of the shelves.  You will have to decide if that meets your style needs or if you have to do something more elaborate.
« Last Edit: September 14, 2023, 12:19:36 am by CatalinaWOW »
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #51 on: September 14, 2023, 02:00:17 am »
Quote
UNF rod that strength computes to 3500 lbs per rod

Out of curiosity, how did you get 3500lbs? I took the area of the 5/16" rod and multiplied that by 70,000. From my understanding, this number is the "maximum" where the rod will stretch/deform and not return; thus making it more likely to snap.

When I discussed this with the ME (Mechanical Engineer), he used a "safety" factor (which, as an EE understand, and practice it myself), but I don't remember the safety number. Even if the safety factor is five, and using 3500lbs that you got (which is lower than the 5369 I got), that's 700lbs per rod giving me 1400lbs total support weight.

I've also planned to use fender washers, actually, a fender washer followed by a regular 5/16" washer (or 3/8" if I go with a larger threaded rod).

I also considered using coupling nuts under each shelf so I have more threads grabbing, but this is really deviating from the original topic/question.  My main concern began with the screws holding the shelves not bleeding through the wood fill on the outside sides of the bookcase.
 

Online T3sl4co1l

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #52 on: September 14, 2023, 02:46:12 am »
Well, take yield not ultimate strength -- ultimate means it's stretched and bent way out of shape, long before actually failing.  Depending on the elongation of the particular material and condition.  Yield means only elastic deformation below there; though there may be fatigue accumulating at lower stresses, down to the fatigue limit*, which along with peak loading, are adequate rationale for a generous safety factor.

It may even be that the loading rate isn't a problem, and deflection dominates.  Machine tools are such an example; while machining forces can be quite extreme (most obviously, above the shear limit of the material being cut, at the tool tip..), mostly it's needing so much material to keep deflection down -- that is, stiffness up.  Which means the strength of the bulkier parts doesn't matter so much -- gray cast iron is quite weak material in the grand ferrous scheme of things, but it's excellent for machine tools given its modulus**, compared to other materials of comparable cost.

*If it exists, and only in applicable alloys.  The statistics generally go something like, cycle limit inversely proportional to stress, or some other exponent, and this is true in most metals, aluminum, copper, etc.  Certain metals apparently behave differently, with the statistic being perhaps an exponential increase in life as stress decreases.  Understandably, this is hard to test, and in practical terms, I mean, you don't hear about valve springs snapping on a regular basis in car engines, despite decades of life -- billions of cycles; it's hard for anything to be important enough, for long enough, to even worry about cycle lifetimes this long.

**Which come to think of it... aha, it's rather poor, as it happens.  Which makes sense given the structure (flecks of graphite in an iron matrix; it's so weak because it's literally chock full of "paper"-filled voids which have no tensile strength and are 100% edges, i.e., stress raisers all around).  Which means a more solid alloy, like ductile iron (spheroidal graphite grains), or just plain old steel (no free graphite at all), are technically better.  Compare 66-162 GPa elastic modulus for gray iron (varying over ASTM classes 20 to 60), versus closer to 150 GPa for ductile irons, or 186 GPa for AISI 1020 mild steel.  Contrast with 356 cast aluminum at 72 GPa.  Which, gives an interesting perspective on those home-built machine tools: assuming one has the materials to commit to pouring as much aluminum as a commercial machine has cast iron, you can do about as well as they do!  Gray iron still holds value in being cheaper per volume, and the higher density shifts resonant frequencies lower (as adding more capacitance to a system, which then oscillates for fewer cycles as resonant energy dissipates -- impedance decreases ("stiffness" increases!) and damping improves.

Anyway, in a framing/carpentry context, obviously the wood dominates deflection; cellulose by itself is actually a pretty impressive for being a chain of sugars, but, the porous matrix of unmodified wood leaves it a bit springy.  Not like a book case expects much of any dynamic loading, but to the extent it does, the wall-tie strategy can be designed to provide damping as well as constraining degrees of freedom [sway etc.].  Say, a felt pad between shelf/bracket and wall, so it can slide with friction; or heh, if you really want to get into it, you could consider the effect of acoustics on the wall; maybe a rigid or semirigid (damped) mounting would be beneficial (reduce resonances of the wall itself) would be better than a semi-loose bolting, etc.

Clearly-- just stretch goals if even that, highly speculative, just extending the scope of knowledge here, nothing actually serious. :)

Tim
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Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #53 on: September 14, 2023, 03:39:29 am »
Quote
Well, take yield not ultimate strength -- ultimate means it's stretched and bent way out of shape, long before actually failing.

So your 3500lbs per rod is theoretically accurate meaning I could hang 7000lbs from two rods? Let's for a moment ignore wood and everything, and assume the threaded rod is the only thing in question. If I hung a solid item weighing 7000lbs, the threaded rod would hold it without ever breaking (let's use a few decades as a timeline)?

I'm just trying to wrap my head around just how strong 5/16" threaded rod actually is.
 

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #54 on: September 14, 2023, 04:03:34 am »
Over that kind of time scale, you're going to have some kind of dynamical loading, whether it's just someone bumping into it, or earthquakes (as applicable; maybe not so likely if I should take "bostonman" literally, and even hurricane forces might be fairly modest in a low house one might install this in :) ).  Also of course there's tolerances, but supposing everything ideal.  Or excepting transient loads by the same rationale, yep.

Also, steel doesn't creep at room temperature, so, if it's there for some time, it's there for all time, more or less.

Also give or take environmental, like, there are particular stress-corrosion phenomena to look out for, as well as just, eventually it'll rust through.

Let me actually do it... let's see...

UNC threads are 60° triangular, so the root depth is sqrt(3)/2 the pitch.  Major diameter is 5/16", and pitch is 18 TPI, so that works out to 0.216" minor diameter, the minimum circular cross section (approximately; actual failure would have a "tang" to one side of the mostly-circular patch, the tang being where the thread got wrenched off both pieces), or 0.0367 in^2, or for 1020 CRS,
https://www.matweb.com/search/DataSheet.aspx?MatGUID=10b74ebc27344380ab16b1b69f1cffbb
at 50.8 ksi yield or 60.9 ksi ultimate, gives 1.86k or 2.24k lbs, which to be clear is lbf (poundforce).

7/16-14 similarly gives 0.0773 in^2, or 3.93k or 4.71k lbf.

What you actually get in all-thread may vary; I would assume something very typically either hot-rolled or drawn, and then cold-rolled to form threads, which will be somewhere between sort-of case-hardened from the rolling process, to full-hard CRS.

Threads on bolts are almost exclusively rolled -- it's cheaper that way, and better besides; cut threads are usually specified as such, and usually on specialty parts that aren't worth setting up in a rolling machine.  I'm not actually sure about all-thread, offhand.

Worst case would be cut thread in hot-rolled: no work hardening, annealed condition, plus some stress raisers from the sharp cutter marks (and perhaps a microscopically rough/fractured surface, depending on how clean the cut was).

1020 HRS is 29.7 ksi yield, so about half the above figures, or 1.09k (5/16") or 2.3k (7/16") lbf.  Ultimate is similar.

I'm not sure where 7k came from, unless that was a(n even more?) naive calculation of solid rod rather than all-thread.

Tim
« Last Edit: September 14, 2023, 04:05:30 am by T3sl4co1l »
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Offline CatalinaWOW

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #55 on: September 14, 2023, 04:09:57 am »
Quote
UNF rod that strength computes to 3500 lbs per rod

Out of curiosity, how did you get 3500lbs? I took the area of the 5/16" rod and multiplied that by 70,000. From my understanding, this number is the "maximum" where the rod will stretch/deform and not return; thus making it more likely to snap.

When I discussed this with the ME (Mechanical Engineer), he used a "safety" factor (which, as an EE understand, and practice it myself), but I don't remember the safety number. Even if the safety factor is five, and using 3500lbs that you got (which is lower than the 5369 I got), that's 700lbs per rod giving me 1400lbs total support weight.

I've also planned to use fender washers, actually, a fender washer followed by a regular 5/16" washer (or 3/8" if I go with a larger threaded rod).

I also considered using coupling nuts under each shelf so I have more threads grabbing, but this is really deviating from the original topic/question.  My main concern began with the screws holding the shelves not bleeding through the wood fill on the outside sides of the bookcase.

You must use the area of the rod at the bottom of the threads.  Which isn't 5/16ths.  I used the minimum value specified in the UNC definition for a course thread of 0.252 inch (Google is my friend, I EE by training just worked my way into mechanical stuff.)  It is somewhat larger in UNF (fine thread).

All Tim's comments are valid, but the bottom line is that there is quite a bit of margin.  McM-Carr doesn't say whether the number they give is tensile or yield, but it is extremely likely that the yield strength is below 50,000.  The correct safety factor is subject to a wide range of opinions.  Various industries and applications use values ranging up to four.  But I will never forget, early in my career visiting a potential vendor to make parts for a product I was working on.  One of their jobs was chemical milling on major structural components for the Space Shuttle.  They commented that where the loads on the structure were well understood they were using a 10% safety factor, but when they were less well understood that went up to 20%.

Numbers are all well and good, but sometimes it takes some hands on experience to really trust the calculations.  It isn't easy to set up a several thousand pound tensile test for your rods, but you can convince yourself that there is a lot of strength there by trying to pull a #4 or #6 screw in two. 
 

Online T3sl4co1l

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #56 on: September 14, 2023, 04:49:27 am »
But I will never forget, early in my career visiting a potential vendor to make parts for a product I was working on.  One of their jobs was chemical milling on major structural components for the Space Shuttle.  They commented that where the loads on the structure were well understood they were using a 10% safety factor, but when they were less well understood that went up to 20%.

Yeah, aerospace can get insanely tight on margins.  When full operating history of the member's loading is known -- whether by direct measurement or modeling -- you can pull margins very close indeed.

And the Space Shuttles were never intended to fly, all that many times -- I don't know what they used, obviously they did make repeat trips, but I doubt they expected more than a thousand say, which means fatigue limits can be quite loose.  Not so much for rapidly rotating or vibrating equipment, like the rocket engines -- turbine parts can be tuned for single-digit failure points IIRC(!!) -- and those may indeed be "wear" parts, to be replaced every flight, or regularly scheduled in any case.  Ditto anything like, drag race engines, say.

Likewise, the materials and processing are very well known -- or can be, when there's economic incentive to do so.  Just as we can spend inordinate amounts of time researching every minute detail about say ceramic capacitors, so too can the whole industrial process, from melt formulation to microstructure and working/forming to finish machining, be examined extremely closely.

Conversely, when it's not, it's not.  A36 architectural steel is somewhat notorious as an alloy, because it's....not, it's basically one thing: 36ksi minimum yield.  It's cheap, which is also to say: highly recyclable.  There are some limits on elongation, ultimate strength (min/max), and chemical composition (max of several common elements), but a real sample could contain a fair mix of minor alloying elements, and make quite a metallurgical surprise if you [mis]used it for something technical like tools, or, engine parts or something.  Ditto rebar (which usually has a little carbon, giving higher strength).

Mind, not that A36 can nominally be hardened -- below about 0.4% carbon (it's under 0.3%), you have a very hard time quench-hardening steel at all, let alone to the degree needed for tooling (which needs more like 0.8-1% for plain carbon steel).  But, one might start with random scrap steel and then case-harden it, or a blacksmith might use scrap as a backing, forge-welded to a strip of tool steel for the tip/edge; etc.  Surprise alloys might not matter in normal handling (i.e., bolted and welded structural steel), but once you start doing metallurgical treatments like these, it starts to matter quite a lot.  And when that tool shatters in the quench bucket, after a couple dozen hours pounding away at it... you might just want to blame the alloy, and, rightly so to a fair extent.  (A better craftsman of course either understands and accepts the peril -- like a responsible EE gritting their teeth and selecting Z5Us when cost/density matters and the value spread can be guard-banded, or eventual failure is just less critical e.g. outside of warranty -- or one selects better materials in the first place, when it matters; why risk making a chisel or hammer out of something that could spall off sharp high-velocity chunks near ones' eyeballs?)

In any case, what you get for common hardware store "mild steel", is probably close to what it says on the label.  Generally you can't go down in strength, without it being just literal sponge (slag inclusions, gas pockets, rusted to hell?), in which case, how did they even manage to forge a rod/bar of it at all?! -- but you can go up in strength and end up with lack of flex, or brittle failure, especially after processing like in the above scenarios.  And in any case, we're talking like a spread of a factor of 2, say -- like from HRS yield ca. 30ksi to CRS ultimate at 60 -- plus another factor of 2 to 4, on top of accounting for peak loading, yeah you can have something that's essentially never going to fail due to loading.

The direct electrical analogy is designing to the test: if we need to pass ESD and surge, well, put in a device rated for about ten strikes each, and if it survives, great, that's it, you're done!  Will the equipment survive longer in service?  Well, that's another matter, but it's also rare that protective devices fail like clockwork, and any additional margin on ratings that you've design into the product will keep it that little bit safer.  At least until something else fails, like if you put in the SMA-package TVS (ESD "safety factor" of say 4 or more?) but forgot to get a peak-rated chip resistor beside it that happens to blow from a single 10kV strike...

Tim
« Last Edit: September 14, 2023, 04:52:22 am by T3sl4co1l »
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Offline David Hess

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #57 on: September 14, 2023, 05:15:18 am »
And the Space Shuttles were never intended to fly, all that many times -- I don't know what they used, obviously they did make repeat trips, but I doubt they expected more than a thousand say, which means fatigue limits can be quite loose.  Not so much for rapidly rotating or vibrating equipment, like the rocket engines -- turbine parts can be tuned for single-digit failure points IIRC(!!) -- and those may indeed be "wear" parts, to be replaced every flight, or regularly scheduled in any case.  Ditto anything like, drag race engines, say.

NASA originally considered cracked turbine blades to be a failure however the SSMEs always returned with them so NASA redefined that as a maintenance issue, which is why the SSMEs always had to be pulled and rebuilt, which made hash of the shuttle's proposed turnaround time and cost.

Quote
Conversely, when it's not, it's not.  A36 architectural steel is somewhat notorious as an alloy, because it's....not, it's basically one thing: 36ksi minimum yield.  It's cheap, which is also to say: highly recyclable.  There are some limits on elongation, ultimate strength (min/max), and chemical composition (max of several common elements), but a real sample could contain a fair mix of minor alloying elements, and make quite a metallurgical surprise if you [mis]used it for something technical like tools, or, engine parts or something.  Ditto rebar (which usually has a little carbon, giving higher strength).

Like a 2N3055?

I was trying to make a similar point the other day about why military and aerospace fasteners are worth their cost in some applications, and why I prefer grade 8 bolts in any applications where it matters.


Of course if someone else, like SpaceX, has a cracked turbine blade, then it is a failure.
 
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Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #58 on: September 14, 2023, 05:10:10 pm »
Quote
I'm not sure where 7k came from, unless that was a(n even more?) naive calculation of solid rod rather than all-thread.

It came from the previous calculation in the message thread where the rod can support 3500lbs. If two rods are used, then it could support twice the weight (ignoring weight distribution and external forces).

Quote
or earthquakes (as applicable; maybe not so likely if I should take "bostonman" literally, and even hurricane forces might be fairly modest in a low house one might install this in

I actually chose my user name so people who reply to any postings (from what I've seen, they can be users from many countries) can base their replies on my geographical locaiton if need be. In this case, Earthquacks was in question; which we don't experience many.

 

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #59 on: September 14, 2023, 05:19:21 pm »
Why do you need to suspend this from the roof? My office has wooden walls which would struggle to support a picture frame, so everything is supported by the floor. Bench, shelves, racks, the lot. OK, there is a white board which is solely wall mounted, but it uses lightweight ink :)
 

Offline bostonmanTopic starter

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #60 on: September 14, 2023, 06:16:09 pm »
Quote
Why do you need to suspend this from the roof?

Attic joists - ceiling.

Also, why not? Keep it off the floor, more open floor space, easier to clean, and, because I can. :)
 

Offline CatalinaWOW

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #61 on: September 14, 2023, 07:21:29 pm »
The thing that impressed me most about those incredibly tight margins is that this was before the shuttle ever flew.  All they had was analysis, simulation and some test data from highly similar test vehicles (Atlas, Titan, Delta, X-15 and the like) in somewhat similar flight regimes.
 
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Online T3sl4co1l

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #62 on: September 14, 2023, 08:36:40 pm »
The thing that impressed me most about those incredibly tight margins is that this was before the shuttle ever flew.  All they had was analysis, simulation and some test data from highly similar test vehicles (Atlas, Titan, Delta, X-15 and the like) in somewhat similar flight regimes.

And at that, mostly mockups, models -- they didn't have anywhere near the computational modeling tools we do today!

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Offline David Hess

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #63 on: September 15, 2023, 09:31:47 am »
The thing that impressed me most about those incredibly tight margins is that this was before the shuttle ever flew.  All they had was analysis, simulation and some test data from highly similar test vehicles (Atlas, Titan, Delta, X-15 and the like) in somewhat similar flight regimes.

And at that, mostly mockups, models -- they didn't have anywhere near the computational modeling tools we do today!

They had strain gauges, lots of strain gauges.
 

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #64 on: September 15, 2023, 05:10:40 pm »
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Offline 5U4GB

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #65 on: September 16, 2023, 10:55:58 am »
And the pro way is to use dowels and glue.
No reason for filler, it's invisible when done correctly. Not really possible to do with a hand drill, you need a drill press plus additional tooling.

That's the way I'd do it too, but you need a set of quite sizeable clamps for that since you no longer have the screws pulling the joint tight, really depends what the OP has access to.
 

Offline 5U4GB

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #66 on: September 16, 2023, 11:05:39 am »
Even with 1-1/16" poplar, a 48" wide shelf may sag, particularly if loaded with heavy books (e.g., 10" deep).

Just converted that to something I understand and yeah, 1.2m unsupported filled with books is going to be a stretch.  For my bookcases I used something like 30mm nosing glued and brad-nailed to each shelf, which hugely increases the load-carry capacity of the shelf and prevents sagging.  The shelves were also supported at the back (it's a closed back) so there's no chance of any sagging, and there's a ton of weight on those bookcases.

Literally.  There's extra bearers under the floor for that room.
 

Offline 5U4GB

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Re: Which Screws Are Safe For Building a Bookcase
« Reply #67 on: September 16, 2023, 11:15:34 am »
From reading the replies, it looks like the yellow Deckmate screws could bleed through over time.

I'm not familiar with Deckmate but the name and yellow colour implies they're <brandname>cote coated, designed for use outdoors in treated timber which just eats standard zinc-coated screws if there's any copper involved (CCA, ACQ, etc, there's almost always copper involved), rather than standard yellow zinc, so you may not get bleedthrough from them.

OTOH if you're working indoors with untreated timber then you can probably use anything since you're not going to expose the screws to anything nasty.
 

Offline bostonmanTopic starter

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Re: Which Screws Won't Cause Bleed through on Wood Filler For Bookcase
« Reply #68 on: September 25, 2023, 01:25:13 am »
I changed the subject to accommodate my original question more accurately.

Just an update: I took a weight of all the wood. Each shelf weighs 10lbs and the sides weigh 16lbs each, totaling 92lbs in wood weight.

Also, I bought stainless steel Torx screws, and have begun painting the wood. Hopefully by the weekend or next week I'll try screwing it together.
 

Offline bostonmanTopic starter

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Re: Which Screws Won't Cause Bleed through on Wood Filler For Bookcase
« Reply #69 on: October 12, 2023, 05:20:32 pm »
I discovered something interesting.

In order to get an idea of how wood fill would look, I took a junk piece of Poplar, drilled a hole, filled it with the wood filler, let it dry over night, and placed a layer of clear stain over it.

The section that didn't have the wood filler dried overnight as usual, however, the section with the wood filler has remained tacky for about a week now. It's less tacky than the first two or three days, but still, tacky.

On a side note, I may just keep the screws exposed as I like the look. They are countersunk, the holes have a coat of poly, and the screws are stainless steel. The look is appealing to me, so I may go with that.

I considered buying a boring bit to use pegs, but this Poplar has many different shades. I have one that has a black line down the side, another is dark, others are light, etc...)
 


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