IPMS-USA Journal: 'Build your own vacuum chamber'

You can do wonders with a $5.00 used vacume machine motor........ I built my own 18 in X 18 in table vacume machine for vacume forming various items. All you have to do is have a vacume chamber and the vac motor with a instant release valve. I think that would suffice for an air removal for RTV, etc. When evacuating the air from any mold material all you need is about a

30 second to 1 minute vacume to remove the air and pour......The vacume motor does not have to run until the mold material cures. The air does not return to the medium, however, you can also put vacume on the piece after the pour to insure that all of the air has been evacuated and the mold material has entered every tiny expanse.

I'm jealous dude. I'm completely mechanicaly inept. I don't have the ingenuity or skills to build my own mechanical stuff. Let us know how that lathe goes. It will be interesting to see what you cobble together. I need to get one for myself, but I'll probably end up buying one and spending more than I need to.

Rusty White Flagship Mdoels Inc. flagshipmodels.com

I will be buying the lathe ,I went to an auction a few weeks ago and missed out on a Harrison M300 in first class condition. Went for a good price though ,although a bit high for me at the time. Just depends on the ebb and flow of the finances , trying to justify it to the Minister for Finances and War , I have explained that I can do jobs with it for money , which will help pay for it and my hobby .

I beleive if you try and vac resin it usually 'flies' out of the mold and makes a mess. I've only ever vac'ed the RTV .

"Rusty White" wrote

Rusty, you might want to reconsider that as they are placed there for a reason.

KL

What happens is you exceed the vapor pressure limit and it boils.

I seem to be a maverick here. I do not use either vacuum or pressure to do resin casting in rtv molds. Neither for mold making or the resin pour itself. Yet I have little problem with bubbles.

I think like an air bubble. Make sure the pour sprue has some pressure head- at least one inch above highest point in mold cavity. Sprue should be J shaped- never bring resin into TOP of cavity.

Every local high spot in cavity MUST have a vent tube.

If these three rules are followed you'll have little trouble with bubbles in resin.

For the molds, most RTV now sold doesn't have too much of a bubble problem. I do not like fast setting rtvs, primarily 'cause it rushes me too much. But I think the slower setting rtvs also allow better filling in of voids and avoidance of bubbles.

I seem to be a maverick here. I do not use either vacuum or pressure to do resin casting in rtv molds. Neither for mold making or the resin pour itself. Yet I have little problem with bubbles.

I think like an air bubble. Make sure the pour sprue has some pressure head- at least one inch above highest point in mold cavity. Sprue should be J shaped- never bring resin into TOP of cavity.

Every local high spot in cavity MUST have a vent tube.

If these three rules are followed you'll have little trouble with bubbles in resin.

For the molds, most RTV now sold doesn't have too much of a bubble problem. I do not like fast setting rtvs, primarily 'cause it rushes me too much. But I think the slower setting rtvs also allow better filling in of voids and avoidance of bubbles.

I use the Smooth On brand of rubber and resins ,I buy the starter packs which have enough of each to do quite a few molds and castings. I make sure that when I mix the rubber components that I don't stir too vigorously so not to introduce any air into the mix.When I pour it into the mold box I pour slowly and from a decent height to let any air escape. BTW I store my RTV and resin components in a fridge in my shed ,Ive had the last lot of stuff I bought for over two years , I thought it would be useless by now ,but I poured a mold a week ago ,and it seems ok . I will try the resin this weekend and see what it does.

I was having a LOT of problems with resin that seemed to go bad. People suggested I was getting too much moisture into resin. What I found was that components of resin seperate out. This is the individual parts, not after it is mixed. I used to invert and return each bottle once. That turns out to have been inadequate if resin has sat for awhile. Now I take each part (resin and hardener) and invert and turn back five complete times. I have had no problems since then- the resin ages quite well in basement.