Screw Holes in Resin

[IAmTheClayman]

Just a quick question: if you're going to be casting a piece that needs to be screwed to something else (planar face to planar face, to specify) how do you handle that with your master? Do you make some kind of mark on the surface? Do you tap the hole ahead of time so that it appears in the cast piece? Do you make a smooth hole?

Thanks in advance!

 

[harryhoudini]

Unless you have uber A++ skills in casting, or if you can cast with zero bubbles then go for the casting with the thread. But if your skills are average (like mine [emoji28]) then cast the hole smooth. Resin is soft enough that if you tap it won't be that difficult. As long as the screw area is a big or bulky piece that's fine. But if your model is thin then that's a different story. You might break the resin piece if too much pressure is added on the tapping.

Hope this helps and Happy moldeling!


Sent from my iPhone using Tapatalk

 

[andy19422]

I use brass push in inserts for my holes.

 

[Teddz]

what andy said... inserts.

If there's to be any sort of force on the screws, the resin won't hold up and the threads will strip. This includes over tightening. You won't need much to utterly destroy the thread.

If you absolutely need to thread the resin, you can either cast the hole smooth or just fill the hole on the master leaving a small indent of where the hole is, then drill & tap it after. I would go for this option as casting the hole (smooth or not) could cause the piece to lockup in the mold and result in possible damage to the mold to get the casting out.

And if you don't want to put too much strain on the material when you tap it, go with a slightly larger drill bit... Example: if your tap is a 6mm, the drill needed - normally - would be a 5mm (0.1968), use a slightly larger 5.2mm (0.2047) bit. The screw may not be as tight as with a thread made in a 5mm hole, but it's tight enough to do the job and you won't be putting as much pressure on the resin while tapping.

 

[Great_Bizarro]

Depending on the size of the hole/screw required, you can probably use one of these. Might be able to cast them in place.
http://www.amazon.com/E-Z-Threaded-..._2?s=industrial&ie=UTF8&qid=1452430776&sr=1-2

 

[IAmTheClayman]

I use brass push in inserts for my holes.

what andy said... inserts.

Depending on the size of the hole/screw required, you can probably use one of these. Might be able to cast them in place.
http://www.amazon.com/E-Z-Threaded-..._2?s=industrial&ie=UTF8&qid=1452430776&sr=1-2

Completely forgot that inserts were a thing. But I'm a bit confused about how I could cast it in place. Since they tend to have a slot at one end wouldn't the resin end up inside the insert during the pour?

EDIT: I've seen people using heat (ie pressure from a solder) to push the inserts into plastics. Would you want to do this for resin? What if you were cold casting? Or is the safest/easiest route to just use press fit inserts (ie http://www.mcmaster.com/#standard-threaded-inserts/=10mj5qf)?

 

[Teddz]

Some inserts have a knurled finish around the body and all you do is drill a hole (or if the hole is cast in place) and drop in the insert. Usually it fits tight and all you do is push it in and you're done, but a little CA or resin will keep it in place if it needs it.

 

[Great_Bizarro]

I was thinking you could use a wooden dowel that is just small enough to thread into the insert to keep the resin out and have the other end stuck in the clay you use to dam up the mold perimeter or poke it through the silicone and back it with clay to seal it. I would be hesitant to put a screw into it in case the resin decided to grab onto it, but a bit of some lube that would not screw up the resin might work.