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Spookydad
02-03-2012, 12:07 PM
I am casting some thumb knobs out of resin. These have to match an antique style and I don't want to make them individually out of brass, although this could be done. Anyway, I was wondering if anyone had any experience/tips/warnings of using a helicoil style of insert in #8-32?

The knobs won't get daily use but need to be reasonable robust.

Any thoughts?

Neil

DFMiller
02-03-2012, 12:20 PM
Neil,
I have used this style before in Polycarb. They can be pressed in or you can mold them in.
http://www.spirol.com/mkt/rs1.php?search=9&gclid=CLbh2YCogq4CFQF6hwodMArY6A


Or you could go with the mode readily available style and cut some grooves axial grooves in them so they are cast in place and wont turn out. I would probably use a nylon screw in them so they did not fill up with resin.
http://www.woodcraft.com/Product/2001048/2806/832-Brass-Threaded-Inserts-10.aspx


Good luck
Dave

Spookydad
02-03-2012, 12:47 PM
I haven't had good luck with cast in place inserts in the past.

I never thought of the ones designed for wood. I think I have a few around somewhere. I will have to dig them out and try them.

Neil

garagemark
02-03-2012, 12:56 PM
I have used many of the Woodcraft inserts (Woodcraft headquarters is one mile from my house). They do an excellent job, are easy to install (make your own tool) and look nice too.

Mark

rowbare
02-03-2012, 01:27 PM
If you are going to cast them in and you are worried about them threading out, take 3 or 4 longitudinal cuts with a hacksaw to thread depth along each insert. That will interrupt the threads and leave a groove for resin.

bob

Spookydad
02-03-2012, 02:33 PM
Usually the problem I have with cast in place is the resin has a tendency to move the insert and they don't sit straight during the curing process. A proper jig would probably help this but in the past I have drilled and tapped afterwards. I don't think the plain resin threads are going to work this time.

Neil

Rosco-P
02-03-2012, 03:03 PM
Something like these would probably work better: http://www.mcmaster.com/#threaded-inserts/=g3anx3

DFMiller
02-03-2012, 03:48 PM
Neil,
I have used that type I linked to in cast polyurethane. You can drill the hole and press them in after the fact. Just get the hole the correct size.
Dave