Hi all, I’ve had a bit of a trawl through the archives regarding this topic but I can’t seem to get a definitive answer. Basically I want to cast a 3/16 stainless thread in polyester resin and be able to coat it in something to facilitate it’s removal later on. Just a little project I’ve been messing around with. Any help would be greatly appreciated. Cheers.
PVA. Or, a light silicone spray lube.
Thanks Bill. I have a can of silicone in the shed. I’ll give it a try and report back.
make solid resin then tap desired thread size after hardens??
I have considered that. I’ll probably try it.
Hi, I’ve casted metal bolts in resin several times and putting oils or sprays on the metal creates a soft surface to the resin closest to the thread. You also lose accuracy with the thread as oils tend to sit in the valleys of the thread, The resin seems to emulsify with the oil and leaves a rubbery surface that never sets sharply.
Pick a solid seperator like a wax that creates a thin barrier but doesn’t mix with the resin. I’ve wiped wax on but don’t dip if you need accuracy.
Pour on a warm day, allow the resin to set and shrink away from the bolt/ rod.
Are you trying to create a functional female thread ?
No clue what you are up to but if you are needing strong threads there are a couple methods better than fiberglass.
Slightly on the expensive side would be Heli-coil. $40 for a kit. There is a good chance that threads can be created via a tap and then a stainless steel insert is applied. Thread on the outside and inside of this insert.
Inexpensive would be the entire insert that can be purchased at a hardware store for $1. Again, stainless. I have used this in fiberglass fins before and it works. Threads on the outside and inside. Larger than the Heli-coil.
All stainless will oxidize over time.
Dave
I haven’t worked with polyester resin since switching to epoxy few years back, so I don’t know how the silicone would work, although I assume Bill’s advice is solid as ususal - but I know silicone is an absolute no-no with epoxy, just wanted to mention that in case anyone gets ideas. You can search the archives for more info if interested.
Thanks for all the advice. Much appreciated. Basically I’m going to set up a number of tests and see which method works the best. Threaded inserts are an option, but I’ll look at that if the resin doesn’t work out.
So much good information on this site. I wish it had been around when I started making boards!
Petroleum jelly is the ticket, used it many times
I tried a number of release agents and they all worked. So did no release agent, so that’s what I’m using.
Bingo. SS with either poly or epoxy will be just fine as long as your mold (e.g. bolt) is new and has no nicks. Once the resin begins to kick, turn the bolt a 1/4 turn out then back in and repeat until the resin is fairly hard.
Hard to get anything to stick to Stainless steel.
I’ve tapped fiberglass for 1/4-20 machine threads with good results and strength, but I had 1/2 inch of threads, and wound up adding an Brass insert and adding more fiberglass over that, as I like overkill.
I used car wax on the Stainless steel bolt just incase the epoxy tried to stick to it.
Don’t use anything. Use some cabosil in the resin going around the thread too, toughen it up a bit.
Let it go really hard then warm up the bolt before attempting demold.
