Self Clinching Nuts

[Dorothy Bradbury]

How do M3 Self Clinching Nuts (-2 type) grip 1.4-2.3mm sheet metal,
when the serrated nurl & self-clinching bit are only about 1.2-1.3mm?

The serration grips ok re rotation - but they can be tapped out easily
since the press can't reach a 1.2-1.3mm thick part in a 2.3mm sheet.

I tried pressing a small steel cylinder into the 4.75mm hole to squash
the self-clinching bit, but it didn't seem to improve the clamping much.

I thought they were supposed to have a bit of push-out resistance?

 

[Jim Thompson]

How do M3 Self Clinching Nuts (-2 type) grip 1.4-2.3mm sheet metal,
when the serrated nurl & self-clinching bit are only about 1.2-1.3mm?

[snip]

Self-clinching nuts? Just dunk them in ice-water ;-)

...Jim Thompson

 

[John Woodgate]

I read in sci.electronics.design that Dorothy Bradbury <dorothy.bradbury

How do M3 Self Clinching Nuts (-2 type) grip 1.4-2.3mm sheet metal,
when the serrated nurl & self-clinching bit are only about 1.2-1.3mm?

They don't, as you found. You must use nuts designed for the material
thickness that you are using.

 

[Dorothy Bradbury]

They don't, as you found. You must use nuts designed for the material

thickness that you are using.

They are Hank-Clinch nuts, M3-alt -2 spec with h=1.37mm for the
serrated-section & clinch section combined (rest is the actual nut bit).
Which seems to contradict the claim of 2.3mm max sheet thickness.

Guess I'll have to email them, it seems logical that h should be more
than 2.3mm so serration-&-clinch span the sheet & clamp like a rivet.

 

[Spehro Pefhany]

How do M3 Self Clinching Nuts (-2 type) grip 1.4-2.3mm sheet metal,
when the serrated nurl & self-clinching bit are only about 1.2-1.3mm?

The serration grips ok re rotation - but they can be tapped out easily
since the press can't reach a 1.2-1.3mm thick part in a 2.3mm sheet.

I tried pressing a small steel cylinder into the 4.75mm hole to squash
the self-clinching bit, but it didn't seem to improve the clamping much.

I thought they were supposed to have a bit of push-out resistance?

You really shouldn't use them in most situations where the nut isn't
retained by the screw after assembly, IMO. In particular, you have to
be very cautious about using them in CRS- pay *close* attention to the
Rockwell numbers and possible changes for the worse due to
cold-working.

Best regards,
Spehro Pefhany

 

[Joerg]

Dorothy, brief question: 1.4 to 2.3 mm is pretty thick for M3. Can't you
have it tapped? That should also save money.

Depending on the application I usually prefer sheet metal screws, or
self-tapping if I absolutely have to. Lowest cost and they usually stay
there forever. Even our roofer used them, per manufacturer's specification,
for a metal roof that has a 50 year warranty. My clients usually frown upon
this kind of idea but once in production they love it.

Regards, Joerg.

 

[Dorothy Bradbury]

I thought they were supposed to have a bit of push-out resistance?

You really shouldn't use them in most situations where the nut isn't
retained by the screw after assembly, IMO. In particular, you have to
be very cautious about using them in CRS- pay *close* attention to the
Rockwell numbers and possible changes for the worse due to
cold-working.

Noted - the nut is retained by the screw after assembly, I was just
puzzled at "clinch height" being so much lower than max sheet thickness.

 

[Walter Harley]

Depending on the application I usually prefer sheet metal screws, or
self-tapping if I absolutely have to. Lowest cost and they usually stay
there forever [...]

....till the equipment has to be disassembled for repair and subsequently
reassembled, and the self-tapping screws become self-stripping screws.

 

[Dorothy Bradbury]

Dorothy, brief question: 1.4 to 2.3 mm is pretty thick for M3.

Can't you have it tapped? That should also save money.

It could, however...

Depending on the application I usually prefer sheet metal screws, or
self-tapping if I absolutely have to. Lowest cost and they usually stay
there forever. Even our roofer used them, per manufacturer's specification,
for a metal roof that has a 50 year warranty. My clients usually frown upon
this kind of idea but once in production they love it.

o Item needs to be removeable for component access
---- self tappers aren't a re-usable machine thread
o Other side of the sheet is a moulded sorbothane shock absorber
---- so need to minimise fastener ingress into that area - re sway space

Hence I had originally used 2.3mm HE30 to allow tapping

So I'm actually going to go the other way:
o If I'm using a metal clinch-nut, I don't need that thickness of metal
o I might as well use cheaper thin-steel & press-fit nut

That regains some sway space, is a bit lighter, and gets a re-usable thread.

Amusingly the supplier's tech support don't know how to get them to
work with the suggested maximum thickness of sheet metal either

Aluminium is nice stuff, but it does love to smear.

 

[Jim Thompson]

Depending on the application I usually prefer sheet metal screws, or
self-tapping if I absolutely have to. Lowest cost and they usually stay
there forever [...]

...till the equipment has to be disassembled for repair and subsequently
reassembled, and the self-tapping screws become self-stripping screws.

"Repair"? That's downright un-American ;-)

...Jim Thompson

 

[Dorothy Bradbury]

...till the equipment has to be disassembled for repair and subsequently

reassembled, and the self-tapping screws become self-stripping screws.

Which nicely tapped holes in HE30 can become when someone leans
a bit too far on an allen key and... ooops, now it's a nice /clearance/ hole.

I wonder if half the PCs in the landfill are there because none of the screw
holes have any thread on them, partly due to USA UNF v ex-USA metric!

Of course, self-tapping screws have a cunning solution.
You simply keep using ever larger self-tapping screws

 

[R.Legg]

How do M3 Self Clinching Nuts (-2 type) grip 1.4-2.3mm sheet metal,
when the serrated nurl & self-clinching bit are only about 1.2-1.3mm?

The serration grips ok re rotation - but they can be tapped out easily
since the press can't reach a 1.2-1.3mm thick part in a 2.3mm sheet.

I tried pressing a small steel cylinder into the 4.75mm hole to squash
the self-clinching bit, but it didn't seem to improve the clamping much.

I thought they were supposed to have a bit of push-out resistance?

Perhaps your drill hole is too big, or punches worn. You get better
results inserting in the 'sharp' side of a clean punched or drilled
detail.

They are meant to be self retaining, not knock-out proof. In normal
use, forces are applied in the pull-in direction.

Make sure you are using the right fastener and plate material
conbination for the job, although you can usually sub harder fasteners
in softer sheet material - it may require hole tolerance tightening
and pressure adjustment. Do not re-use.

RL

 

[R.Legg]

Aluminium is nice stuff, but it does love to smear.

Refering to chromate?

Self fastening alloys react with chromate, whether in Aluminum or
Steel. If fasteners are installed prior to passivation, you should use
stainless varieties.

RL

 

[John Woodgate]

I read in sci.electronics.design that Dorothy Bradbury <dorothy.bradbury

o Item needs to be removeable for component access
---- self tappers aren't a re-usable machine thread

Look at http://www.taptite.net/faq.asp

 

[Tim Shoppa]

o Item needs to be removeable for component access
---- self tappers aren't a re-usable machine thread
o Other side of the sheet is a moulded sorbothane shock absorber
---- so need to minimise fastener ingress into that area - re sway space

Hence I had originally used 2.3mm HE30 to allow tapping

So I'm actually going to go the other way:
o If I'm using a metal clinch-nut, I don't need that thickness of metal
o I might as well use cheaper thin-steel & press-fit nut

There's an amazing range of fasteners available in the aviation
industry for doing things like what you want. They aren't necessarily
cheap, though. And they may not be available as small as M3.

Tim.

 

[Dorothy Bradbury]

Look at http://www.taptite.net/faq.asp

Thanks for that, gone to look.

Re smear I mean aluminium's tendency when tapping/machining.
It's a nice material, but takes a little care when working with it.

Redesigned it quite a bit - lighter, partly in nylon, dropped the # of
parts & fasteners by over 75% by using a sheared & press-braked
piece of thin aluminium to retain the sorbothane moulding.

So the self-clinching nuts will be used on a thin shield over 3 stacked
1U open frame PSUs, and as an airflow duct re 92mm front fan used.

 

[Dorothy Bradbury]

Thanks for that taptite site - those are perfect for elsewhere.
Will also have a run thro the aero industry fasteners too.

 

[maxfoo]

Which nicely tapped holes in HE30 can become when someone leans
a bit too far on an allen key and... ooops, now it's a nice /clearance/ hole.

I wonder if half the PCs in the landfill are there because none of the screw
holes have any thread on them, partly due to USA UNF v ex-USA metric!

Of course, self-tapping screws have a cunning solution.
You simply keep using ever larger self-tapping screws

or just use HeliCoil® Screw Thread Inserts.

http://www.emhart.com/products/helicoil.html






Remove "HeadFromButt", before replying by email.

 

[Spehro Pefhany]

Thanks for that taptite site - those are perfect for elsewhere.
Will also have a run thro the aero industry fasteners too.

Don't know about availability in the UK (metric or not), but you might
want to have a look at http://www.pennfast.com/ as well.

Best regards,
Spehro Pefhany

 

[Dorothy Bradbury]

Thanks for all the help.