Appropriate Screw for 2mm hole in ABS

Kinda OT for s.e.d, except it's for holding a PCB into a case...
I'm using one of these-here cases for a product I'm designing:
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They have little bosses inside for screws for the PCB, the bosses have
holes that are 2mm x 6mm (I know, I know, metric is for unpatriotic frog
lovers -- but that's how it's specified).
The cases come with screws to hold the halves together, but they're
leaving me on my own vis. what screws to hold the PCB in with. So --
what's the right screw for this hole?
The PCB is fairly light (no herky transformers, motors, etc.),
unstressed (no honkin' big wires or soldered-on switches), basically
just a board that gets bolted to a box.
So -- what screw to use? And how much penetration into the hole should
I plan for?
TIA.
Reply to
Tim Wescott
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Any reasons why not to use 2mm screws? I would use 2x4 (mm).
Reply to
linnix
designing:
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They have little bosses inside for screws for the PCB, the bosses have
A 2mm machine screw is slightly smaller in diameter than 2mm, so it would certainly be an easy fit. The board might not be all that secure, though.
Are you suggesting a 2mm sheet metal screw, or some other self-tapping screw whose nominal diameter is the hole size, not the OD of the screw threads? If so, what?
Reply to
Tim Wescott
ave
an M2 screw will fit through a 2mm hole ;)a M2.5 should be a perfect fit, size wise but the thread is a big fine for plastic.
any who, first hit "bopla screw" on google is:
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-Lasse
Reply to
langwadt
Reply to
John Fields
Just a note: I sent an email to Rose+Bopla, not really expecting a reply. I just got a call from Candice at their US office, who was very helpful and is going to make sure that someone even _more_ helpful calls on Tuesday! After I figured out it wasn't a sales call (who responds to emails with a _human voice?!?_ I was delighted.
Wow. I was already happy because they're nice enclosures -- this is even better.
Reply to
Tim Wescott
es have
Yes, 2mm normal body diameter, self-tapping, with the threads slightly bigger.
Tell them to include the screws, so they won't screw their future customers.
Reply to
linnix
Well ... that diameter is pretty close to the tap drill size for a 3-48 screw. So -- you could tap it to that size -- or get one of the self-tapping screws (sort of like dull-pointed wood screws with less taper) for use in plastics.
Or -- you could heat and push in a knurled metal nut for a smaller screw -- say an 0-80, because the OD of the thread for anything larger will be too large to work with the existing holes.
Not sure how well a thread-forming tap would work in the plastic involved, otherwise I would advise those to form standard threads.
Good Luck, DoN.
Reply to
DoN. Nichols
Done very often with plastic cases. Should not be a problem holding PCB.
Reply to
linnix
Threaded fasteners are all designed to provide specified fastening for a mated thread count of 3 threads. Granted, many application where a bolt gets turned down a blind hole results in many more then 3 threads of captivation, the design spec gives us all we need with only 3.
So, IF the bosses are already threaded, your screw only needs to be your PCB thickness plus say 4 or 5 thread pitches more.
If they are not threaded, you use the same formula for whatever size screw (#4 or #6) you decide to thread the hole with and use. If you intend to use a washer for the screw to bear against instead of your PCB, you would also add that thickness. For metal cases, one usually leaves one of the PCB mount holes as a grounding point. For metal some use thread locking compounds. For plastic, you shouldn't need it as you will not be meeting any vibe specs anyway. :-) also with plastic, you could opt to press (or melt) in PEM nuts instead of threading holes in plastic.
After all that the screws are usually already made so you have to choose one from the lengths available that most closely matches your final requisite length sum.
Reply to
SoothSayer
"Flexural Modulus".
Absolutely perfect choice. A variant of sheet metal and wood screw thread topology.
Very informational link/page, thanks.
Reply to
SoothSayer
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Yes -- but it depends on the plastic involved. Yes, the cases are likely to be made of a plastic which will gracefully accept thread-forming taps (and should be so made) -- but *some* plastics don't like the stresses involved, don't flow well enough, or (perhaps) are sensitive to lubricants (e.g. Plexiglass/Acrylic will develop cracks radiating from any point which combines stress and oils.)
Enjoy, DoN.
Reply to
DoN. Nichols
e
Tim:-
This is a ME question. Suggest that you refer to data from companies that make screws designed specifically for threading into plastic, don't guess on this one. Here is a starting point:
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Textron is another supplier.
You should be able to request the ABS resin spec sheet from the manufacturer, otherwise use a generic ABS resin spec eg. maybe 350,000 PSI for the flexural modulus
Best regards, -sp (currently in Jena, former East Germany)
Reply to
speff
designing:
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They have little bosses inside for screws for the PCB, the bosses have
Yup. I was hoping that either s.e.d would have someone who's done this before (apparently not!) or that r.c.m would have some semi-ME types with concrete suggestions.
So far I've gotten two leads to Accument, if the case manufacturer doesn't get back to me then I'll probably see if Accument will sell me a couple of hundred screws, or point me to a catalog distributor.
I'm really hoping that the case manufacturer (who designed the bosses, after all) has a recommended screw, but they're all off for the long weekend.
Reply to
Tim Wescott
es have
I already posted the link to boplas site with the recommended screw for different boss sizes:
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-Lasse
Reply to
langwadt
designing:
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>>    They have little bosses inside for screws for the PCB, the bosses have
I've been following this (I'm curious about the proper fastener, as well). The Bopla link above is helpful but the numbers cross right back to itself.
The 2.5 mm size makes sense but trying to find the right piece at, way McMaster-Carr is proving to be a challenge.
Reply to
Rich Webb
designing:
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They have little bosses inside for screws for the PCB, the bosses have
This
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looks promising. They have the virtue of being made of obtainium.
Reply to
Rich Webb
snip
snip
Try Ababa.
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Not sure, but one more possible source can't hurt.
Reply to
Chieftain of the Carpet Crawle
designing:
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They have little bosses inside for screws for the PCB, the bosses have
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It's their German site, and in-house numbers which don't seem to be available at Digi-Key. So it's not necessarily help for ordering the parts from an establishment that's going to want to deal in small quantities, in the US, unless Rose + Bopla does themselves. It's certainly not a help in getting an independent source.
But who knows -- I have a promise that a human being from Rose + Bopla will be contacting me Tuesday; we'll see.
Reply to
Tim Wescott
osses have
ok I thought with a part number you would be able to get it from where you got the boxes
any who, something like this:
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to be what the plastic boxes I have laying around uses
-Lasse
Reply to
langwadt

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