Author Topic: Looking for tiny U-channel  (Read 9207 times)

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Offline beanflying

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Re: Looking for tiny U-channel
« Reply #50 on: August 08, 2022, 02:20:14 am »
Get a price on having it 3D metal Printed as you have gone with a one piece block design and already have it in STL format. So Shapeways or a similar more local service depending on what is nearby.

By the time a job shop runs a few operations and cuts your dovetail you will chew up a fair bit of labour even though the material cost is minimal. A small solo operator job shop will be likely cheaper here because of the fiddle factor too.
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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #51 on: August 08, 2022, 02:51:01 am »
PCBWay quotes $600 for machining of 20 parts. The same part 3D printed is $400 for aluminum and $800 for the cheapest steel. Shapeways quotes $1200 for the same part in steel (20 pcs as well).

I also need to figure out the requirements. I think all those auto-quoting services assume minimal radius of 2 mm. My part as is is not possible using endmills. That corner is 60 degrees and is trivially machined using 60 degree cutter.

I don't mind redesigning the part for the process, there is no real reason to have those sharp corners. But I don't know what to design for. I don't think those automated quoting systems are that smart anyway.

Ultimately $600 is not that expensive. But there is nothing in this part that really needs CNC and a job shop may be able to handle it better. But those obviously don't have auto quoting.
« Last Edit: August 08, 2022, 02:52:57 am by ataradov »
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Offline beanflying

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Re: Looking for tiny U-channel
« Reply #52 on: August 08, 2022, 03:05:03 am »
Pricing for low volume then Printed seems not to bad.

I would think twice about setting up a Router/Mill to make it for that price for a one off. Doing a run is a different thing.

Rough cut the stock (check what is a readilly available size available to reduce costs) so 1-2mm longer than finished. Generally extruded section will already have a broken corner so no radius needed. If they need to machine to your size will add a lot of cost.

'Generally' Dovetail cutters are a hard sharp corner (there is in reality a tiny radius on most of them) so this will be ONE setup assuming there is no squaring up or dimensioning of raw stock other than to length. A second bit will generally be required here to finish it to length (so a bit swap) So these two operations will be done vertically.



After this the part will need to be rotated 90 degrees (unless they are using a 4th or 5th axis which is really unlikely for this) to have the holes drilled/bored and or reamed (depending on what tolerance you want.

So machining it is a fiddle.
« Last Edit: August 08, 2022, 03:07:36 am by beanflying »
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Offline JohanH

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Re: Looking for tiny U-channel
« Reply #53 on: August 08, 2022, 07:40:32 am »
Here are some great tips how to reduce cost https://www.hubs.com/knowledge-base/reducing-cnc-machining-costs-design-tips/

You could also ask local CNC companies (they are everywhere). I had a stainless steel plate water cut by a local company and it was really affordable.

I once ordered a prototype for a special aluminium part from https://www.jevny.com/. They were not expensive, but shipping wasn't cheap. It was a straightforward cut, though, no turning of parts.
 

Online Ian.M

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Re: Looking for tiny U-channel
« Reply #54 on: August 08, 2022, 09:28:45 am »
Why does the jaw have to be one piece?  If you use a separate plate with a beveled edge on top of the jaw block to make the asymmetric V groove, it would be well within the capability of what can be made with hand tools in a home workshop.   Drill and tap the jaw block for a bunch of small countersunk machine screws to hold the top plate rigidly in place.

Whether it works out cheaper than sending it out for machining or 3D metal printing depends on how competent you are in a workshop, and the cost of your time.   If you cant file or grind to a line while maintaining a reasonably constant angle, then $600 for 20 parts is a good deal!
 

Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #55 on: August 08, 2022, 04:07:26 pm »
I live in an apartment in downtown San Jose. I have no access to any machining equipment. Otherwise it would not be a problem and instead of spending $600 on parts, I'd spend that on a Grizzly mill and slowly make them myself.

I'll ask for "manual" quotes after I get back from vacation. Almost none of the dimensions are critical. The part is 12 mm high right now. It could be made out of 1/2"x1/2" square stock without doing any machining to the stock sides. Just cut the groove and drill the holes. But those things can only be worked out with a person on the other end.
Alex
 

Offline Nominal Animal

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Re: Looking for tiny U-channel
« Reply #56 on: August 08, 2022, 06:58:42 pm »
I'd consider it in two parts, too.  One part would be the ½"×½" square with four holes; two horizontally for the threaded rods, and two vertically for fastening to the ftop part.

The top part would be e.g. ½"×⅛" flat bar, with one edge milled to the 60° angle (30° off vertical) needed.  Two short countersunk bolts would fasten it to the first part.

I live in a city apartment also, and don't have any power tools at all right now, but I do have enough aluminium to do a few pairs if I wanted to.  I happen to have 12mm×12mm anodized aluminium square tubing (Alfer brand, from a hobby store) with 1mm wall thickness, and 2mm flat bar (actually 20mm×20mm L profile or something).
I should even have a suitable 3mm tap and 5mm long 3mm countersunk machine screws, and a couple of 20cm pieces of 4mm or 5mm threaded rod with matching nuts.

Aluminium is soft enough to file by hand to the desired angle, and even a hand whisk drill is enough to drill the needed holes with a good sharp bit; no problem.  Instead of a file, I'd actually use wet or dry sand paper at 120, 240, and 400 grit, on top of a mirror, with WD-40 as the lubricant, as that's easier and faster than hand filing.  Even the angle is easier to control.  (I do have some wood chisels I use elsewhere, that I keep sharp using that same method.  I even have all my fingers left, with just a couple of dozen old battle scars here and there; nothing bigger than three or four stitches, though.)
For the countersink, a larger drill bit will do fine.
 

Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #57 on: August 08, 2022, 07:15:51 pm »
If I'm doing it at home, then I don't see why two parts are particularly easier. And I think the slot does not really need to be that shape. I'm pretty sure even ~2mm diameter groove would work too. And in a pinch that can be carved with a dremel fixed to the bench.

It is just at $30/part, it appears too expensive. For $15/part I would not think twice ordering them. But may be that price is not viable indeed.
Alex
 

Offline Nominal Animal

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Re: Looking for tiny U-channel
« Reply #58 on: August 08, 2022, 10:34:54 pm »
If I'm doing it at home, then I don't see why two parts are particularly easier.
Sanding the edge (or edge and corner, if you want) on a sheet of sandpaper on top of a mirror is quick work, just a couple of minutes; and no dust or such if you use WD-40 or just Windex as the lubricant.  You can get surprisingly accurate groove between the two parts this way.  Plus you can just change the top part if you nick it, need a different edge angle or something.

It is just at $30/part, it appears too expensive. For $15/part I would not think twice ordering them. But may be that price is not viable indeed.
One would probably need to make several dozen pairs to recoup the setup costs.  Someone with a Bridgeport mill and suitable alu stock could batch them out in an hour, and then it might make sense.

If you use OpenSCAD, here's a quick sketch of what I was thinking about:
Code: [Select]
$fn = 64;
color([0.5,0.6,0.6, 1]) difference() {
    translate([-6,0,-6]) cube([12,200,12], center=true);
    translate([-6,0,-6]) cube([10,210,10], center=true);
    translate([0,-80,-6]) rotate([0,90,0]) cylinder(h=50, r=3, center=true);
    translate([0,+80,-6]) rotate([0,90,0]) cylinder(h=50, r=3, center=true);
    translate([-6,-60,-5]) cylinder(h=10, r=1.5, center=true);
    translate([-6,60,-5]) cylinder(h=10, r=1.5, center=true);
}

color([0.5,0.7,0.7, 1]) difference() {
    translate([-6,0,0.5]) cube([12,200,1], center=true);
    rotate([0,30,0]) translate([0,0,1]) cube([2,210,4], center=true);
    translate([-6,-60,2]) cylinder(h=4, r1=1, r2=4, center=true);
    translate([-6,60,2]) cylinder(h=4, r1=1, r2=4, center=true);
}
If you use countersink machine screws with nuts and washers for the top side, you can adjust the exact placement of the top by drilling slightly oversized holes to the square tubing.  May need needle-nose pliers or sticks of wood to hold the nut while you tighten it, though.
 
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Offline beanflying

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Re: Looking for tiny U-channel
« Reply #59 on: August 15, 2022, 10:49:05 am »
While this is away from the OP wanting a DIY option I ran across this on Aliexpress and it might be a good option for others https://www.aliexpress.com/item/4000180543028.html?spm=a2g0s.8937460.0.0.3eb62e0efNkm3E and it is sort on the same basic concept.

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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #60 on: August 15, 2022, 03:57:03 pm »
One of my iterations had this "frame" design. I did not like it at all. The unused part of the frame and the handle stick out a lot and it get hang up on the stuff around, including the microscope stand. And it is very frustrating when you get carried away while looking though the microscope and one position adjustment clears the table for you.

Even with my design, the plan is to have multiple versions with bolts shortened as needed. And possibly jaws shortened too, although that was not a real problem and 80 mm jaws worked fine for all the boards I tried.

It might be a good candidate for parts though. I'll need to look into it.
Alex
 

Offline Jay_Diddy_B

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Re: Looking for tiny U-channel
« Reply #61 on: August 15, 2022, 09:34:02 pm »
Hi ataradov and the group,

This is my version of a PCB holder for microscope work:



This is a link to the thread:

https://www.eevblog.com/forum/projects/pcb-holder-for-smd-assembly-microscope/

I cut a small dovetail in the jaw:



It cut it square on the milling machine and then filed the angle by hand.

I also made a plastic version, 3D printed:



Thread: https://www.eevblog.com/forum/projects/pcb-holder-for-smd-assembly-3d-printed-edition/

Both have there uses, the metal one is better for soldering, the plastic one is useful for testing.

I would make the prototypes with a 3D printer. I was able to print the 1/4-20 thread, but I had to clean it with a hand tap.

I have used both on a daily basis for the last 7 years.

Jay_Diddy_B
« Last Edit: August 15, 2022, 09:35:49 pm by Jay_Diddy_B »
 
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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #62 on: August 15, 2022, 09:42:12 pm »
Oh, wow, this is the same exact design.

I've been experimenting a bit, and it looks like you don't even need an angled undercut. Just a straight cut is mostly enough to hold the board. The pressure when soldering is minimal and is mostly directed downwards.
Alex
 

Offline thm_w

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Re: Looking for tiny U-channel
« Reply #63 on: August 15, 2022, 10:32:18 pm »
Jay_Diddy's thread has a lot of good info, the stickvise is interesting: https://www.digikey.com/en/products/detail/3197/1528-1747-ND/6198266 https://www.stickvise.com/hacks/diy-upgrades
Its more complex to build but allows faster adjustment of the width. You could buy a few of those and cut one of them down to a smaller size.

But I think you have to swap the nylon jaws out for alu or ptfe as well?

Also:
https://www.aliexpress.com/item/1005002494437140.html
https://www.aliexpress.com/item/1005004378477193.html
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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #64 on: August 15, 2022, 11:22:23 pm »
I already explained why stickvise does not work for me - the central rod interferes with the components on the board. It only works for one side, but once you have components and flip the board, the stick starts to get in a way. And in practice adjustment of the width is not something I do a lot. That is not a real issue.

And those "Mijing" things are horrible. There is a reason they only show 3D renders. The actual hardware is really bad. The fit and finish is very poor, so they always jam and lock up.
Alex
 

Offline thm_w

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Re: Looking for tiny U-channel
« Reply #65 on: August 15, 2022, 11:33:46 pm »
I already explained why stickvise does not work for me - the central rod interferes with the components on the board. It only works for one side, but once you have components and flip the board, the stick starts to get in a way. And in practice adjustment of the width is not something I do a lot. That is not a real issue.

And those "Mijing" things are horrible. There is a reason they only show 3D renders. The actual hardware is really bad. The fit and finish is very poor, so they always jam and lock up.

That would just mean making a taller jaw to clear the component in question (since the stock nylon jaw is not usable regardless), not saying its an option for you, just something DIY'able for others.
But yes good point, that is the downside of the single rod.

Would be possible to have the quick adjust system and two thinner rods on either side then.
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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #66 on: August 16, 2022, 12:10:32 am »
Would be possible to have the quick adjust system and two thinner rods on either side then.
This was one of my prototypes. Instead of where threaded rod is now have two smooth rods and then the system changes to 2 actual jaws (one fixed and one floating on the rods) and one clamp on the size of the floating jaw. There are springs between the floating jaw and a clamp. So, you still have wide open working area and can adjust spring tension using the clamp position relative to the floating jaw.

I prototyped that using 3D printed parts and it worked, but was not ideal, since plastic jammed on the floating jaw. I assume with metal and tighter tolerances it might work.

Then the design evolved into what I have now and I really see no issues with it. If you need spring jaws, then you can add springs between the nuts and the floating jaw.

But again, given the minimal grip, all you need is half a turn on one side to free the board. Large travel adjustment is a bit more annoying, but how often do you readjust it? I typically have one board I'm working on at a time.

Alex
 

Offline thm_w

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Re: Looking for tiny U-channel
« Reply #67 on: August 16, 2022, 12:40:41 am »
True, if you have one board and multiple size vices, then wouldn't need to adjust much.
You used steel rivnuts right, no issues with sticking when turning at all?

Two options I can think of for rod, threaded rod and the thumb-nut or just using a cap screw + 3D printing a thumb knob for it. Second requires no cutting, but might not look as nice.
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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #68 on: August 16, 2022, 12:51:31 am »
You used steel rivnuts right, no issues with sticking when turning at all?
Nope, it is very smooth. I originally tried to tap the 3D printed hole, but it was very hard to tap it straight, especially by hand. And without straight holes this square frame becomes wobbly.

The only issue that I have with this design is that when travelling large distance, you need to turn the knobs at about the same rate if you want to push the jaw, otherwise it tends to jam. But in a typical operation you just slide the jaws together and then adjust the nuts however you need, it is not a problem. And I expect it to be less of a problem with a hole drilled in a metal.
Alex
 

Offline Jay_Diddy_B

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Re: Looking for tiny U-channel
« Reply #69 on: August 16, 2022, 02:14:36 am »
Hi


The only issue that I have with this design is that when travelling large distance, you need to turn the knobs at about the same rate if you want to push the jaw, otherwise it tends to jam. But in a typical operation you just slide the jaws together and then adjust the nuts however you need, it is not a problem. And I expect it to be less of a problem with a hole drilled in a metal.


I spent some time messing with the size of the holes.

I just checked the one on my bench, the 1/4-20 threaded rods measure 0.240". The holes measure 0.277", this is an odd size in imperial, but it is 7mm in metric. The over-sized hole on the loose jaw causes the jaw to twist when the clamping pressure is applied, this why I used the dove-tailed notch.

The jaws are 5.00 inches wide, the rods are on 4.250" centers. The jaws were made from 6061 Aluminum.

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Offline beanflying

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Re: Looking for tiny U-channel
« Reply #70 on: August 16, 2022, 02:33:13 am »
Maybe dump the threads all together. Thumb screws are easy to make or buy, 6mm parallel rod is common as muck all over evilbay for 3D Printers and a couple of 2mm Roll Pins to lock the fixed jaw to them.

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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #71 on: August 16, 2022, 02:52:40 am »
Maybe dump the threads all together.
I thought about that and did a crude prototype. This does not work too well. There is nothing maintaining the clamping pressure. And screw turning action loosens the clamping. Again, it is possible that metal version will actually work. Or a version with a more complicated clamp design, not a simple screw pushing on a rod.

In the screw design there is enough flexibility that things just wedge together and provide solid pressure.

And so that screws are not in a way, they can be placed on the side of the block.
« Last Edit: August 16, 2022, 02:55:52 am by ataradov »
Alex
 

Offline beanflying

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Re: Looking for tiny U-channel
« Reply #72 on: August 16, 2022, 03:05:55 am »
You really don't want clamping 'pressure' you only need to hold the board in place and resist 'sliding' along the jaw. The board held down by the dovetail against the rail is plenty of contact area but it could easily be increased with a scuff up with 80 or 120 grit sandpaper on the shelf (I really don't think it would be needed)

You would be surprised the deflection you can get in a PCB when you clamp in from the sides to aggressively, depending on the method used this is one of the issues with holding them for PCB Milling (skunkworks project in progress). Depending on what you are soldering or reworking this might cause you other issues with component failure from physical stress.
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Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #73 on: August 16, 2022, 03:11:30 am »
That's what I meant by the "pressure". I did not mean cranking like a real vice. But in my experiments (with a single rod), the board would still slide. But I need to try that with metal jaws. 3D printed jaws did not work for that. But I can imagine that plastic is not ideal for this case.
Alex
 

Online ataradovTopic starter

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Re: Looking for tiny U-channel
« Reply #74 on: August 16, 2022, 03:32:19 am »
Ok, this is cool. I prototyped a metal version from random stuff I had around. And it actually works quite well.

The key here seems to be that the holes in a free jaw are larger than the rod. This way when you are clamping and applying hand pressure before tightening the screws, the jaw is slightly crooked. Tightening the screw straightens the jaw, simultaneously clamping the board. Slightly "tugging" on the board still loosens it, but the "jaws" here are not ideal either. Full groove may be better. And the tugging necessary may be harsher than what you will get with soldering. But wicking, may cause that amount force.

So, more experimentation is required and this is worth investigating for sure. I like this design more than the screws.
Alex
 
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