Resin casting and bubbles: would this work?

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adamata

Sr Member
RPF PREMIUM MEMBER
So, I am casting a set of parts for the training remote and the last piece is a small round part with a very thin post.

When I pour the resin, the post is so thin that air gets trapped in the post. I have tried several different ways to get the air out, but I am getting mixed results and its a real PITA.

So, here is my question.

Could I pour the resin and then put these molds in a vacuum chamber to suck out the air bubbles trapped in the thin areas?

Would that work?
 

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Leigh

Sr Member
RPF PREMIUM MEMBER
I'm no expert & I'm learning myself but can you not make a hole/chanel in the mould to let the trapped air out???
I guess you would end up with a bit extra on your cast but you could just cut that off :confused Maybe
 

Finhead

Sr Member
Leigh is correct if your able to I would put another vent hole. If that is not an option you normally want to pressure cast not vac. The main issue with that is you would want to pressure mold as well.
 

adamata

Sr Member
RPF PREMIUM MEMBER
ok, so what I didn't explain is that this piece is about 5mm in diameter and the post in the center of it is about 2 mm thick and about 4mm tall.

it is VERY SMALL :)

like I said, the post diameter is the same as the smallest air bubble.

crazy small.
 

Etewaf

Active Member
I personally have not had any luck with vacuum degassing resin. You could get a resin that takes longer to cure and maybe get away with it. I made a similar thread a while back and the piece of advice that I got was to powder the mold, and that worked for my purposes, but your piece sounds quite intricate.
 

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Finhead

Sr Member
Pressure casting will work fine then, but you will most likely need to redo the mold as a pressure mold or you will get surface imperfections as the resin pressures against the mold.

ok, so what I didn't explain is that this piece is about 5mm in diameter and the post in the center of it is about 2 mm thick and about 4mm tall.

it is VERY SMALL :)

like I said, the post diameter is the same as the smallest air bubble.

crazy small.
 

trooper

Sr Member
RPF PREMIUM MEMBER
have you tried the baby powder trick? just dust the mold with it and knock out the rest, i laughed the first time i heard it, but it works great :)
if that does not work, pm me, I would be glad to help in this project :) maybe i can make a pressure mold and cast these for every one :) lmk
 

Sith_Lord_Hritz

Well-Known Member
RPF PREMIUM MEMBER
what if you used a syringe/needle to inject a small amount of resin into the mold after you fill it like normal. Then it would push out the air and leave resin in its place. you can get needles from the drug store i think.
 

Sith_Lord_Hritz

Well-Known Member
RPF PREMIUM MEMBER
Also i think i read someware that if you plan to vac resin in a mold then you will first need to use a vac when you make the mold as well.
 

Alan Castillo

Master Member
RPF PREMIUM MEMBER
A toothpick or an upside-down needle to slowly mix/move the resin before it cures could also release any air trapped in pesky corners.
 

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Superkrates

Active Member
RPF PREMIUM MEMBER
Venting is the best solution, but this may be the same problem I had with air getting trapped at the bottom when pouring resin into a mold for heat-sink fins - no amount of pressure would eliminate the bubble totally (venting was not an option) and I couldn't get powder into the small opening to eliminate the wall adhesion while pouring resin.

Two things that can be done:
Pour resin, then 'drag' the problem area (for this application you'll need a thin, stiff wire with it's end rounded as to not damage the mold) to break the wall adhesion and let the air rise out.
-or-
insert a plastic tipped syringe near the lowest point and inject resin into the area (the cavitation of the injected resin aids in venting the cavity.
 

trooper

Sr Member
RPF PREMIUM MEMBER
Also i think i read someware that if you plan to vac resin in a mold then you will first need to use a vac when you make the mold as well.

i think what you are referring to is pressure casting, if you want to pressure cast resin, the silicone mold needs to be pressure cast as well. Ive not heard of vacu casting, but doesn't mean anything :)
 

franz bolo

Sr Member
You can pour the posts first and use a toothpick to get the bubble out, Then continue pouring. All depends on how you made the molds.

You can even let the posts harden and then come back and pour the rest. Resin sticks to resin.

FB
 

Jumpergal

Member
if it's that small and will be painted, is there any other way of getting the look without the casting? If it's the size of a wire, I mean, can you use a wire on a ball of Milliput or something? Sorry if this is off base, I was just trying to visualize what you're referring to.
 

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Rebelscum

Sr Member
A couple things...

Bubbles get bigger in a vacuum, so that's not good for resin.

Vacuum silicone to remove bubbles as they expand and pop. If you don't do that, the rubber will have tiny holes just under the surface you can't even see, but when you then pressure the resin it will PUSH the resin into those bubbles and make tiny pimples on your cast.

Pressue makes bubbles in the resin smaller.

If you have a tiny piece, probably you gotta figure out how to get the bubble to escape during the pour as it sounds too big for even pressure to make it disappear. Sometimes I'll pour a tiny bit, squeeze the mold, rotate it, etc, to see if I can get it to work its way out. On a larger mold you would probably even see it come up, though this sounds so small, you may not see it.
 

adamata

Sr Member
RPF PREMIUM MEMBER
Ok, so here is the piece. Bottom row, center. Mind you, that stem is about 2mm thick. I might have another solution, but thanks for all the advice so far. I might try a few things before i resort to plan B

 

trooper

Sr Member
RPF PREMIUM MEMBER
i think i have that kit, is it from the same tank as the parts above it?

if so i'll cast em up :)
 

trooper

Sr Member
RPF PREMIUM MEMBER
:lol crap, i thought it was an easy fix :)
lmk if i can help

jerry
 
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