Author Topic: sheet metal drill bits?  (Read 2666 times)

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Online coppercone2

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sheet metal drill bits?
« on: May 03, 2022, 04:05:49 am »
Does anyone know of a drill bit set meant for drilling sheet metal that has the geometry required to make nice holes? I don't mean a step drill, I mean like a twist drill with special points.

I see some theories about something along the lines of crown point drill bits for drilling sheet metal nicely. I got a set of acrylic drill bits a while back and I am very happy I got that, so I was thinking it might be nice to have for sheet metal.

I.e. something like this
https://qrpbuilder.com/wp-content/uploads/2016/11/sheet-metal-drills-a.pdf
« Last Edit: May 03, 2022, 04:16:46 am by coppercone2 »
 

Online bdunham7

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Re: sheet metal drill bits?
« Reply #1 on: May 03, 2022, 04:12:53 am »
Black and Decker 'bullet' drill bits are sort of like that.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline WattsThat

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Re: sheet metal drill bits?
« Reply #2 on: May 03, 2022, 04:41:34 am »
Standard bits work fine using this machinists old trick. (start at 5:50 if you just want the method without the drama):


« Last Edit: May 03, 2022, 04:45:12 am by WattsThat »
 
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Offline metrologist

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Re: sheet metal drill bits?
« Reply #3 on: May 03, 2022, 04:42:10 am »
Also maybe you seen the YT vids of the machinists fold a small piece of denim cloth over their hole and drill through that. The swarf get wrapped up with the cloth and bit which prevents it from grabbing and tearing through. I haven't tried it.
 

Online coppercone2

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Re: sheet metal drill bits?
« Reply #4 on: May 03, 2022, 04:46:07 am »
I was hoping there was a drill bit solution, those cloths look great but I find myself dealing with sheet metal enough that I don't think I would mind buying a specialized drill set, if it exists. That might be useful if you need a non standard hole and like letter drills on a sheet metal. For number drills I don't know, they seem too small for a cloth.
 

Offline jpanhalt

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Re: sheet metal drill bits?
« Reply #5 on: May 03, 2022, 10:22:29 am »
Any single point cutter will work, particularly if done in a rigid setup.  Of course, step drills are in that category, but you eliminated them from consideration.

When working on aircraft sheet metal, a wider included angle (i.e., 135° vs. 118°) is often used.  That helps with small holes.  In fact, they are sometimes referred to as "aircraft drills."  You can get sets in number, letter, and other dimensions.
 

Offline langwadt

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Re: sheet metal drill bits?
« Reply #6 on: May 03, 2022, 11:40:42 am »
 
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Offline eugene

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Re: sheet metal drill bits?
« Reply #7 on: May 03, 2022, 02:55:24 pm »
Maybe not "machinist approved", but at home I use bits intended for wood to drill sheet metal. The B&D Bullet drill sets are available at your local hardware store. Or: https://www.mcmaster.com/drill-bits/point-style~brad/
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Offline metrologist

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Re: sheet metal drill bits?
« Reply #8 on: May 03, 2022, 04:22:57 pm »
Most that do enough of this will look at a punch.
 

Online coppercone2

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Re: sheet metal drill bits?
« Reply #9 on: May 03, 2022, 04:46:06 pm »
How similar is the hand ground drill to the pilot point drills? So I guess I basically want a 135 degree pilot?
 

Online TimFox

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Re: sheet metal drill bits?
« Reply #10 on: May 03, 2022, 04:57:10 pm »
I know you rejected step drills, but I find them very useful for sheet-metal drilling.
My favorites are the "Unibit" brand (Irwin) that have a single cutting edge, and leave very clean round holes in metal, say 1/16" thick, starting with a pilot hole equal to the minimum diameter of that bit (e.g., 3/16").
The larger ones are designed to enlarge holes, and need an initial hole cut with a self-starting bit (such as the 3/16" minimum type).
(I prefer them to competitors' products that have multiple cutting edges.)
They are available in fractional inch sizes (minimum 3/16 inch diameter), but also in metric (even mm values, minimum 4 mm diameter).
https://www.irwin.com/tools/browse/drill-bits/unibit-step-drills
« Last Edit: May 03, 2022, 05:01:46 pm by TimFox »
 

Offline BrokenYugo

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Re: sheet metal drill bits?
« Reply #11 on: May 03, 2022, 05:02:42 pm »
AFAIK step drills are more or less the gold standard. Hand grinding/sharpening a brad point is tricky and I doubt those pointy tips last long cutting metal.
 

Offline alpher

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Re: sheet metal drill bits?
« Reply #12 on: May 03, 2022, 07:21:06 pm »
As somebody suggested, don't drill, punch ✊
 

Offline jpanhalt

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Re: sheet metal drill bits?
« Reply #13 on: May 03, 2022, 07:52:03 pm »
AFAIK step drills are more or less the gold standard. Hand grinding/sharpening a brad point is tricky and I doubt those pointy tips last long cutting metal.

Most important, it appeared he was using too fine a stone for re-contouring.  Notice the bluing he got.  The problem I have had doing work on small aircraft is that you usually need to go through more than one thickness for rivets.  Moreover, it is rare to use anything more than 1/8" on ordinary sheet metal.  That is where the 135° bits come into play.

AFAIK step drills are more or less the gold standard. Hand grinding/sharpening a brad point is tricky and I doubt those pointy tips last long cutting metal.

Ageed.  Redoing a drill's point by hand requires skill.  "A drill follows its point."  That is why I like my drill sharpener (a great TDR/SRD unit).  It's old but like new and not worn out (attached).  I have known far better machinists than me who could do that by hand.

 

Online coppercone2

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Re: sheet metal drill bits?
« Reply #14 on: May 03, 2022, 08:28:41 pm »
I think maybe the step drills I have are dull, I might buy a extra set for thin metals and another set for 1/8+

I might have ruined it drilling 10+ gauge steel a few years back, it does not feel sharp compared to a fresh one. The bit went from welding thickness metal to being used on essentially tin cans and that might be the problem, people seem to agree the unibit is better then the other bits.

The only benefit is that you can be sure you wont over size a hole freehand using a modified bit.

I was doing holes in thicker metal (maybe 12 AWG) and the bit felt very grabby/inconsistent.

What is the highest quality step drill brand? Maybe I will see if norseman sells it. Is M42 or maybe carbide a good choice for material for this?

How about those hole saw drills sold in the electrical section of the hardware store? (i.e. klein), they look kind of like magnetic drill hole saws (usually SDS), the electrician ones have carbide teeth.
« Last Edit: May 03, 2022, 08:35:15 pm by coppercone2 »
 

Offline jpanhalt

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Re: sheet metal drill bits?
« Reply #15 on: May 03, 2022, 08:36:26 pm »
Get a good bit of HSS and learn how to sharpen it.  Doesn't change the diameter much.  My Unibit with 3/8" long steps (max 1/2") is at least 40 years old.  Still works great.
 

Online TimFox

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Re: sheet metal drill bits?
« Reply #16 on: May 03, 2022, 08:54:43 pm »
I don't recommend the electrician's-style hole saws for good holes in sheet metal.
There is another style, more expensive, designed for sheet metal that I have used for shallower holes:  https://www.mcmaster.com/hole-saws/hole-saws-for-sheet-metal-11/cutting-depth~1-8/
There are also ones with more depth than 1/8 inch.  Full list:  https://www.mcmaster.com/hole-saws/hole-saws-for-sheet-metal-11/
For step drills, I recommend the Unibit brand from Irwin.  They are available in different formulations.
 

Offline themadhippy

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Re: sheet metal drill bits?
« Reply #17 on: May 03, 2022, 08:58:28 pm »
holesaws tend to leave a rough edge,ok if your putting a bush or grommet in,but need a bit of filing to get  a smooth finish.
 

Online TimFox

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Re: sheet metal drill bits?
« Reply #18 on: May 03, 2022, 09:11:05 pm »
That's a problem with the "electrician's" hole saws.  I've had better luck with the shallow-cutting ones I cited above.
 

Offline eugene

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Re: sheet metal drill bits?
« Reply #19 on: May 03, 2022, 09:11:23 pm »
I have a few punches for larger holes, but who has every size that might be needed? They're relatively expensive. Also, I don't know what sizes are available, but there is definitely some minimum hole size that is practical.

Step drills are useful for a few holes, but tend to be slow.

I'm going to reiterate my support for the kind of bit in the OP; something with a sharp point at the center and two 'fly cutter' points that are sharp and shaped well. Depending on the size of the fly cutting points and the thickness of the sheet metal, comparatively little material gets cut. You end up making little washer shaped things. It's quick and results in a very clean hole. No pilot hole is required as with a punch or step drill. The sharp point means that even a center punch isn't necessary (especially if, like me, you tend to put the punch in the wrong place anyway.)

I doubt aluminum is any harder on the tool than wood. Even with mild steel they should last a long time. Toss it out and buy a new one when it reaches end of life. Cheaper than step drills or punches.
« Last Edit: May 03, 2022, 09:13:05 pm by eugene »
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Offline alpher

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Re: sheet metal drill bits?
« Reply #20 on: May 04, 2022, 12:26:53 am »
For smaller holes in sheet metal nothing beats an "ironworker",  :) :D
But at home this thing costs less that quality drill set and does much better job in sheet metal than any drill bit you can afford:
https://www.princessauto.com/en/metal-punch-kit/product/PA0008019921
Princess Auto is pretty much a canadian Harbor Freight.
 

Offline metrologist

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Re: sheet metal drill bits?
« Reply #21 on: May 04, 2022, 05:20:15 am »
Or maybe a Rotex or TinKnocker is more appropriate for a home-ish kind of shop?

https://www.penntoolco.com/tin-knocker-18-station-hand-turret-punch-tk-18/
 

Online coppercone2

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Re: sheet metal drill bits?
« Reply #22 on: May 04, 2022, 05:28:00 am »
I thought maybe if I was to do punches I would get a micromot mini-press and dies for it, but I am not sure at the moment what it could handle. or some larger arbor press. With a chuck and bushings/pins it looks like you might be able to get any sized hole you want, so long the bushing can be fixtured somehow, perhaps in another larger chuck

not sure what the force requirement is. that thing does 250lb

Actually I am thinking, you can do this in a drill press... its already heavy duty, enough for dealing with shields and screens

https://www.americanmachinetools.com/tonnage_punch_hole.htm
« Last Edit: May 04, 2022, 05:47:20 am by coppercone2 »
 

Online coppercone2

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Re: sheet metal drill bits?
« Reply #23 on: May 04, 2022, 06:52:53 am »
I had another idea, maybe its possible to work harden metal by peening or something, then drill it?

I wonder if that would make it better or worse, might try tommorow
 

Offline jpanhalt

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Re: sheet metal drill bits?
« Reply #24 on: May 04, 2022, 09:43:41 am »
Another perpetual thread on how not to drill a simple hole?  :=\

How about using a TiG torch with the gas turned off.  Then grind the edges?  If that doesn't work, turn the argon on.  Ordinary stick welding is also used.  Of course, don't forget the ballistic method(s).  That allows a wide choice of diameters...
 


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