Can I use any fasteners in abs plastic or is there some special requirement like how fiberglass shouldn't have threads?
Can I use any fasteners in abs plastic or is there some special requirement like how fiberglass shouldn't have threads?
I googled what kind of fasteners are for abs plastic. I didn't really get a clear answer. That's why I asked it here.
More info required;
What loads will the thread be subjected to?
Will the thread be cut or moulded into the ABS, or will a threaded insert be used?
How thick is the ABS?
Are the fasteners to be removable?
I need a way to attach the straps to the helmet.
You need to use some kind of thread form cutting fasterner
Here is the M3 plastic thread we used for ABS
Yes, we bought our thread form cutting fasterner from McMaster Carrr and it works well
For light loading, you can also use sheet metal screws
EDIT: be careful to use this kind of screw for plastic with fiber glass since you might crack the plastic - you need to open the hole a little bit larger on Plastic with fiber glass
I think it should be noted there is an important difference between thread-forming and thread-cutting fasteners. Both exist for use in plastics.
Thread cutting is used on brittle plastics and thermosets, etc. This actually cuts threads by removing plastic material. I would not trust these for any re-installation applications - the chance of getting it realigned perfectly is low so you'll likely cut out the thread you made on the initial install and be left with next to nothing.
Thread forming is used on ductile plastics, such as most thermoformed plastics and includes ABS (I'm pretty sure fibreglass reinforced ABS is included with these). This doesn't remove material, rather displaces it to fill the gap between screw threads. These can be reinstalled a limited number of times (different designs/manufacturers claim different amounts but the ones I've dealt with claim 10 re-installations).
The ones in the McMaster-Carr link above are thread forming.
Every helmet I've seen uses threaded inserts and stainless machine screws. It is a good idea to use inserts for anything that will be installed and removed "frequently". I wouldn't cut threads in plastic and expect them to survive unless they are not loaded, and will be installed once, for the life of the part. My .02$
Also, being that it is a helmet, you don't want a self tapping screw self tapping into your skull on impact. That is why you use a threaded insert with a large bearing surface that won't punch through on impact, and is very flat and smooth.
Yes, it's another choice for stronger bond but requires insert molding ( depend how you mold it and it might not possible to put the insert in)
removed "frequently".
True ! the thread form cutting screw is not ideal for this purpose !
Yes, we bought our thread form cutting fasterner from McMaster Carrr and it works well
For light loading, you can also use sheet metal screws
EDIT: be careful to use this kind of screw for plastic with fiber glass since you might crack the plastic - you need to open the hole a little bit larger on Plastic with fiber glass