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“Tap” for sheet metal screws?

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MatBirch

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Filer, Idaho
I have an ongoing issue at work. We build truck bodies, and as the electrician, I’m constantly mounting lights, fixtures, etc with sheet metal screws, usually stainless. Trouble is, often I’m going into either 1/8” aluminum, or 1/8” or 10gauge satin coat galvaneal steel. Not thick enough to tap and use a machine screw, but constantly breaking stainless screws. I can often use a carbon steel self tapper and run it through as a Tap, but it gets wasteful, and frankly a pain in the rear. Typically working with #8, but also 6 and 10.

Any ideas?
 
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PoorOwner

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CA
Electrical boxes are thinner than 1/8 and often tapped or self tapped with 10-32 screws
It forms a couple threads and is to code. Just an example.
 
C

Copymutt

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Not sure of the brand but my go to is a self tapping screw that by design the first 1/4 inch is a cutter/drill to establish the hole to the correct diameter for the threads. Mine are stainless with a wide near flush head.
Pretty sure I get them at HD. Never had one fail.
Jim
 
R

readhead

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That is a problem you will never solve. Stainless is soft. I built a lot of SS kitchen equipment and we always had to tap with a steel screw before we installed the stainless screw. Sometimes you get lucky but after you have had to dig out enough stripped ss screws it just becomes second nature to tap them first.
 
S

ssdave

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I've seen a tool that is a thread starter, threaded like a self tapping screw on the end, and mounted in a screwdriver handle. Run it in a few turns, twist it back out, and then put in the screw. Don't know who makes it, I would search Klein as a likely suspect. Made exactly for what you're asking.

I did a quick search, and Grainger shows a couple of Klein and one Channellock tool. Here's a link that hopefull works:

https://www.grainger.com/category/t...g-tools/tools/ecatalog/N-162bZ1yzffopZ1yzgdeo

https://www.grainger.com/category/tapping-tools/punching-tools/tools/ecatalog/N-162bZ1yzffop#nav=%2Fcategory%2Ftapping-tools%2Fpunching-tools%2Ftools%2Fecatalog%2FN-162bZ1yzffopZ1yzgdeo
 
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MattT

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Feb 20, 2010
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Experimenting with a set of number drills until you find the one that'll give you good thread engagement without breaking screws would be easier than tapping holes. Or maybe you could use a finer pitch screw designed for the thicker metal you're working with like a Tek5. Not sure if they're available in stainless though.
 
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manwithtools

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If you are working with 1/8" and thicker, there is no reason you can't use machine screws. Rule of thumb is three threads of engagement is sufficient for most fastening applications.

10-32, 8-32, 6-32 will all have four threads of engagement in 1/8 material. Use two cordless drills, one to drill the hole and one to tap. It'll save a lot of aggravation, partulary with stainless fasteners. You will be doing the end users a favor as well, if they ever need to R&R a fixture or light, they will thank you.

We build industrial electrical control panels and drill and tap for machine screws hundreds of times a day. Most of our work is now done by a CNC machine, but we are still using machine screws to hold the components to 12 and 10 ga panels.
 
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matt_i

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In 1/8" material, a -32 SAE screw will give you 4 threads.

So your 8-32, 10-32, 6-32 are good as far as machine screws in my opinion.

To speed up the process of tapping, I would use "spiral point taps" or "gun taps" which have an edge geometry which curls the chip ahead of the tap point. This is ideal for chucking into cordless drills because it runs in and out very fast.

Obviously you have the extra step to run the correct sized #25 #29, etc tap-drill first, but you will always have nice threads. It only takes 10-15 seconds to run the tap though. Ideal if you had 2 cordless drills..... Drop of blue loctite if high-vibration.

If you are stuck on self tappers you have to go with MattT's advice, incrementally pick larger drill bit sizes from the 115pc set (using .000 - decimal thousandths as your gage) until you find one which allows you to drive the screw without breakage.

EDIT: The Man With Tools is quicker on the draw today :beer:
 
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manwithtools

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matt_i said:
In 1/8" material, a -32 SAE screw will give you 4 threads.

So your 8-32, 10-32, 6-32 are good as far as machine screws in my opinion.

To speed up the process of tapping, I would use "spiral point taps" or "gun taps" which have an edge geometry which curls the chip ahead of the tap point. This is ideal for chucking into cordless drills because it runs in and out very fast.

Obviously you have the extra step to run the correct sized #25 #29, etc tap-drill first, but you will always have nice threads. It only takes 10-15 seconds to run the tap though. Ideal if you had 2 cordless drills..... Drop of blue loctite if high-vibration.

If you are stuck on self tappers you have to go with MattT's advice, incrementally pick larger drill bit sizes from the 115pc set (using .000 - decimal thousandths as your gage) until you find one which allows you to drive the screw without breakage.

EDIT: The Man With Tools is quicker on the draw today :beer:
Click to expand...

Great advise about the blue Loctite as well. :beer:
 
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manwithtools

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OccupantRJ said:
If you have enough depth behind the part, a drap (drill/tap combo) may do the job for you. Drill and tap in one shot. See mscdirect for examples.
Click to expand...

I hesitate to recommend these for production work. They are expensive and fragile in my experience. If all use was in aluminum you might get a reasonable life from them. If mild steel is involved, don't expect them to be the magic bullet.
 
N

NORDFORD

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Jan 25, 2014
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I’ve got a Customer that installs commercial glass. They were recently using stainless steel #10 x 3/4” pan head torx self drilling screws. These were 18-8 stainless. They called me about broken heads. I looked at the application, made a couple calls and we tried some 410 stainless screws. Problem solved. They are just enough harder to drill through and hold strong. They are mounting two pieces of 1/8 aluminum together.
 
A

adbanshee

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Dec 11, 2011
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Orangeburg County SC
manwithtools said:
I hesitate to recommend these for production work. They are expensive and fragile in my experience. If all use was in aluminum you might get a reasonable life from them. If mild steel is involved, don't expect them to be the magic bullet.
Click to expand...

I agree, I have used them in aluminium with good results, but in a steel SxS frame it snapped after the 3rd hole.
 
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Nor'Easter

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Maine
Why not use self drilling screws...they come in all shapes and sizes, head profiles, drive types, etc. Adding an additional operation let alone two (drill/tap).

10-15 seconds a screw turns into minutes a day, hours a month, so on a so forth. Not to mention the need to always keep specific drill bits and taps in stock.
 
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