Threading help. screwing a steel sheet.

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Threading help. screwing a steel sheet.

Postby gcb » December 14th, 2012, 6:58 pm

think this will be the most 'hardware' thread here... I have to make some holes in a metal sheet, and the initial plan was to use nuts on the back to hold the screws... but then i started thinking about using a taper since they're manual and inexpensive

only thing is, most tutorials i see use them for huge diameters. Would it be wise to use it for M3 or M2.5 (or maybe M2) screws on a thin steel sheet?

I noticed that the original threaded holes on that steel sheet have a small rim pushed inwards to provide more threading area... is there any way i can do those myself? how's it called?
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I assume i need some kind of industrial press to do something like that...?

The sheet is 1mm (i measured up to 1.2 on some points, never got anything smaller than 1.01)

ideally i'd like to screw in those motherboard Hex standoffs... i'm not sure the specs for the thread angle and such... is there any way to find (or how to measure) that?

lastly, what's a good plance to get metric taps? and should i waste time looking for carbide? or steel is enough to hand drill steel?

the hex i'm getting are those
http://dx.com/p/brass-threaded-stand-of ... ece-148715
(yeah, china. nowhere else to get those around here. mcmaster only have short ones in imperial, frys charges 1/3 of that for 4 short ones. amazon and such for small parts are worse than useless)
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Re: Threading help. screwing a steel sheet.

Postby k-ww » December 14th, 2012, 9:03 pm

Poor mans way:

[try these somewhere you do not mind an extra hole first!]

1) drill hole about 1/2 dia of thread in metal.

2) find nail with dia less than that of hole size needed for tap.

3) place block of wood behind sheet metal.

4) hammer nail into hole.

To tap hole,

1) find steel screw of desired thread

2) grind conical taper on tip, and a flat on one side

3) with drop of oil, thread screw into hole
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Re: Threading help. screwing a steel sheet.

Postby UAirLtd » December 15th, 2012, 5:35 am

This is going to be slightly off-topic, but it's related to the thing you said about "small rim pushed inwards to provide more threading area", don't know what that's called, but it reminds me of flow-drilling, which uses friction from a rotating tip to melt a hole, and this provides a big rim inside that is very useful for extending the threading area, here's a video: http://www.youtube.com/watch?v=NhkWINPRK3A Don't know if you can do this yourself, perhaps the one you showed is caused by drilling or punching.
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Re: Threading help. screwing a steel sheet.

Postby semicolo » December 15th, 2012, 12:44 pm

Also it looks like the original screws have high pitched threads, maybe if you use fine threaded screws/taps you won't need the rim
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Re: Threading help. screwing a steel sheet.

Postby gcb » December 15th, 2012, 6:18 pm

UAirLtd wrote:This is going to be slightly off-topic, but it's related to the thing you said about "small rim pushed inwards to provide more threading area", don't know what that's called, but it reminds me of flow-drilling, which uses friction from a rotating tip to melt a hole, and this provides a big rim inside that is very useful for extending the threading area, here's a video: http://www.youtube.com/watch?v=NhkWINPRK3A Don't know if you can do this yourself, perhaps the one you showed is caused by drilling or punching.


That video is pure awesomeness... but i don't think that was the case of the original ones...they are "pushed in" somehow. Looking at the rims cut and border 'damage' it's also clear it was drilled/pushed.

That said, I think getting a kevlar (or whatever those are) "drill" bit and just burning it in instead of finding a industrial press should be easier for me to do...

actually, I just got some low profile nuts from the same place i got my M3 tap, so if the simple drill+tap does not work, will simply bolt some nuts and be done with it :/ man i need a garage to fill with machining tools... :/

now on the damned 3-5 day wait for delivery. worst part of any hack.
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Re: Threading help. screwing a steel sheet.

Postby gcb » December 15th, 2012, 7:10 pm

semicolo wrote:Also it looks like the original screws have high pitched threads, maybe if you use fine threaded screws/taps you won't need the rim


your comment made me look at them with the 10x loupe, they appear to be 3mm wide and one thread per mm. don't think they are that pitched, even though the pic really looks like. or maybe it's just something very close to 0.5 thread from imperial that i can't discern very well with a ruler or cheap caliper.

Here i'm going to confess i'm 100% ignorant of imperial stuff and say that i can't id a imperial screw (or anything for that matter... heck i even bought a german car when i moved to the US so i could keep on only using metric tools), so please help me. I will probably not end up using any of the existing holes from the case, nor the screws, but i think it would be good to know how to ID them.

A quick search showed that imperial screws are named[2] as [diameter if larger than 1/4"]-[thread revolutions per inch], BUT for anything with less diameter than 1/4, you have to use a table to know the actual value (despite the impracticality, how do you differentiate a 2-32 as in it's smaller-than-1/4-2 from the 2-inch ones? anyway...)

Another search says that computer cases[2] switch inconsistently from M3-0.5 and 6-32 (or M3.5052-0.79375)... but to be closer to fool me as a M3-0.5 they would have to be 5-50, but i only found imperial standard thread sizes to be *-48 or *-56... would those also appear to be 1 revolution per mm as the *-50 would?

... ok, i think this is going off-topic and becoming a rambling.

[1] http://en.wikipedia.org/wiki/Screw#Unif ... d_Standard
[2] http://en.wikipedia.org/wiki/Computer_case_screws
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Re: Threading help. screwing a steel sheet.

Postby gcb » December 15th, 2012, 7:14 pm

k-ww wrote:Poor mans way:

[try these somewhere you do not mind an extra hole first!]

1) drill hole about 1/2 dia of thread in metal.

2) find nail with dia less than that of hole size needed for tap.

3) place block of wood behind sheet metal.

4) hammer nail into hole.

To tap hole,

1) find steel screw of desired thread

2) grind conical taper on tip, and a flat on one side

3) with drop of oil, thread screw into hole


i will definitely post pics of what happened with the nail idea.... as soon as i sort out if I will manage to get access to a drill press or will have to drill by eye
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Re: Threading help. screwing a steel sheet.

Postby semicolo » December 16th, 2012, 3:00 pm

I'm not at ease myself with imperial stuff, being born in France and moved to canada when I was 28, don't get me started on that subject.
But just by looking at the pictures the screws seem to have higher pitch than M3 that are supposed to have 0,5mm pitch (that's still half your 1mm pitched screws), so if your sheet is 1,5mm you should be able to have 2-3 threads holding the screw, that might be enough depending what you're doing.
By the way you could measure 4 spaces between threads and divide the length by 4 to get a better measure of the pitch (or more, the more the better)
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Re: Threading help. screwing a steel sheet.

Postby k-ww » December 16th, 2012, 3:29 pm

FYI: This is a generic version of the tooling that made that shape:

http://pdf.directindustry.com/pdf/wilso ... 6-_11.html
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Re: Threading help. screwing a steel sheet.

Postby gcb » December 19th, 2012, 12:38 am

semicolo wrote:I'm not at ease myself with imperial stuff, being born in France and moved to canada when I was 28, don't get me started on that subject.
But just by looking at the pictures the screws seem to have higher pitch than M3 that are supposed to have 0,5mm pitch (that's still half your 1mm pitched screws), so if your sheet is 1,5mm you should be able to have 2-3 threads holding the screw, that might be enough depending what you're doing.
By the way you could measure 4 spaces between threads and divide the length by 4 to get a better measure of the pitch (or more, the more the better)


You guys were totaly right... i was measuring a screw from the plastic panel by mistake, they really look the same, thankfully i had them in plastic bags by steps... those are NOT M3...

they are 2.77mm wide and pitch is like 0.77mm. So eiter a #3 or #4 (or 6/32, i really have no clue how to tell all those apart)

But, today i got my M3 tap... and used the reinforcement steel board that holded the heavy transformer to do some tests.

I started by drilling a 3/32 (2.38mm) hole (realized i have 2 full sets of carbide drills, both imperial) and then tapping with M3. The screw could dance in the hole... awfull.

my second try was to drill with a 5/64 (1.98mm) and then the 3/32, and then tap. (tried tap after the 5/64, but it was impossible)
The screw went in and did not wooble much... but after it entered and exited the hole some 3 times, it started to wooble as well.

So i began to investigate why. Took out the jewlery loupe and started to count the threads inside... On my holes on the 1mm wall, there was about 1.5~2 threads. 3 if you count the last loops very close to the rims, but i guess those are not strong enough to make any difference.

Then i decided to investigate the original holes. The ones drilled on those nice bent rims that gave them another 1mm to play with. There I could screw in and out infinite times and they would still be strong with a single turn!!! i started considering that the brass like material would play better with the steel sheet than my steel bolts... then i looked better at the hole. besides the extra rim, They cheated. there's the same 1.5~2 threads just the same, but the threads are not a single edge, it's two! i tried to take pictures, but taking pics with the loupe is too damn hard for non plane stuff.

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my threads are like:
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the original ones are
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ok, that probably made it more difficult.... it's like they have 2 threads that forms a rail for the screw's threads.

think i will have to use nuts and lots of super glue anyway :( unless i can find a tap that makes those nice rail threads
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