Resin Casting

[LV LOU]

I utilize the same concept. I typically take a shell and attach a "base of 0.060" X 0.125" styrene around the bottom edge to allow a place for the air to escape to. TypicallyI use a fill hole at one end, and vents both sides mid-way and a vent at the other end. I typically put the mold on a sheet of glass and tilt it to where the fill side is lower. When building the mold, I use lego blocks to form the box around the master, with 4-6 pegs to ensure the inner and outer mold halves are correctly positioned/oriented. A well designed mold is the most important aspect of casting. I have also noticed that if I heat the mold under a lamp prior to pouring the resin, the resin tends to set up better, especially when there is more humidity.

If you use pressure,there are no bubbles to deal with.My molds are the shape of the part,with fillholes in the middle,and bleed channels in the corners.My castings come out needing very little cleanup,with just a sharp X-Acto knife on Sunday,I cleaned up 25 steam casting in 1/2 hour.

[kelticsylk]

Can someone post a photo of a mold with the bleed holes and such? I can't visualize how these should look or where they should be located.

[johnh35]

If you use pressure,there are no bubbles to deal with.My molds are the shape of the part,with fillholes in the middle,and bleed channels in the corners.My castings come out needing very little cleanup,with just a sharp X-Acto knife on Sunday,I cleaned up 25 steam casting in 1/2 hour.

I have tried pressure, but saw no advantage to it if the mold was built right to begin with. The thing I did notice about pressure casting was that if the mold had an air bubble in it, it would typically rupture under pressure, ruining the mold. Since I do not have a vacuum chamber to degas the silicone before making the mold, it was probably not as productve as it could have been.

[DKS]

I have tried pressure, but saw no advantage to it if the mold was built right to begin with. The thing I did notice about pressure casting was that if the mold had an air bubble in it, it would typically rupture under pressure, ruining the mold. Since I do not have a vacuum chamber to degas the silicone before making the mold, it was probably not as productve as it could have been.

The solution is quite simple: cure the mold under pressure. I pressurize both the molds and the castings; I have zero air bubbles in my molds, and it's extremely rare to see any in my castings. I do no preparation of the mold materials, either; I just dump the mixed mold material on the master, pop it in the pot, and 12 hours later I have an absolutely perfect mold that will not distort while pressurizing the castings.

[johnh35]

The solution is quite simple: cure the mold under pressure. I pressurize both the molds and the castings; I have zero air bubbles in my molds, and it's extremely rare to see any in my castings. I do no preparation of the mold materials, either; I just dump the mixed mold material on the master, pop it in the pot, and 12 hours later I have an absolutely perfect mold that will not distort while pressurizing the castings.

I tried it that way, but I still ended up with voids in the mold. In the end, I just continued making the molds like I normally did and put the pressure pot aside. I didn't have problems with air bubbles in castings I made, but wanted to experiment with pressure pots.

[LV LOU]

I have tried pressure, but saw no advantage to it if the mold was built right to begin with. The thing I did notice about pressure casting was that if the mold had an air bubble in it, it would typically rupture under pressure, ruining the mold. Since I do not have a vacuum chamber to degas the silicone before making the mold, it was probably not as productve as it could have been.

No advantage? When I went to pressure,it was almost a magical moment.I don't use pressure for molds,though,only castings.The way I pour molds,I have no problems with bubbles in the rubber,and I have a high volume vacuum pump I degas it with before I pour it.

[DKS]

No advantage? When I went to pressure,it was almost a magical moment.

Indeed, such was the case for me. It solved a lot of mold problems, too. I have yet to see a mold that wasn't 100% perfect, every single time.

[LV LOU]

Can someone post a photo of a mold with the bleed holes and such? I can't visualize how these should look or where they should be located.

Here's one of my old ones for a TRIX B unit..My new ones are much better quality,but,no pics at the moment.There are two holes,maybe 1/8',running right up through the core in the shell casting,one on each end,for filling and storage of extra resin to fill the voids that get eliminated when pressurized.My newer molds leave much less flash because they're harder,the flash is like onion skin.That particular shell was cast before I got my pressure pot.....

[LV LOU]

This is the kind of quality you can get using vacuum/pressure..Any of the visible flaws are dust..

[DKS]

Food for thought. Micro-Mark CR600 is equivalent to Smooth-Cast 310. CR600 costs $35.75 for 32 ounces; Smooth-Cast, $25.96 for the same amount (that's their "trial size").

Micro-Mark 10:1 mold material is $45.95 for 2.2 pounds; the equivalent Mold Max product is $25.47 (again, their "trial size").

Mann 200 release spray is $19.40 from Micro-Mark, $13.20 from Smooth-On.

Xtend-It is $24.65 at Micro-Mark, and $20.18 at Smooth-On.

Anyone who does a lot of casting will want to get the gallon-size containers of Smooth-On anyway, and that drops the price even more.

Just sayin'.

[LV LOU]

David,have you bought any stuff lately? I got some resin a few weeks ago from Smooth On,got HAMMERED with the shipping.It was close to 20.00 for a trial size resin,can't remember which one I got.They apparently have to ship everything as hazardous,now.I would imagine it's the same for Micro-Mark..

[DKS]

David,have you bought any stuff lately? I got some resin a few weeks ago from Smooth On,got HAMMERED with the shipping.It was close to 20.00 for a trial size resin,can't remember which one I got.They apparently have to ship everything as hazardous,now.I would imagine it's the same for Micro-Mark..

Yes, I've ordered very recently, and yes they ship everything as hazardous now. However, for me I don't feel it as much because I place pretty large orders--several gallons of resin and mold material--so the shipping becomes a small percentage of the cost.

[jimmo]

David,have you bought any stuff lately? I got some resin a few weeks ago from Smooth On,got HAMMERED with the shipping.It was close to 20.00 for a trial size resin,can't remember which one I got.They apparently have to ship everything as hazardous,now.I would imagine it's the same for Micro-Mark..

I found a local Smooth-On dealer (Reynolds Advanced Materials) so my shipping costs are pretty low. The other advantage is it's within driving distance from my location in case I need something that day, otherwise I get it the next business day.

[jimmo]

The solution is quite simple: cure the mold under pressure. I pressurize both the molds and the castings; I have zero air bubbles in my molds, and it's extremely rare to see any in my castings. I do no preparation of the mold materials, either; I just dump the mixed mold material on the master, pop it in the pot, and 12 hours later I have an absolutely perfect mold that will not distort while pressurizing the castings.

BTW David, the Willmodels acquisitions department (Mrs. Will) has approved the purchase of a pressure pot, so thanks for the technical info and recommend on the supplier.

[LV LOU]

 I'm kinda lucky.It's actually cheaper for me to drive to Smooth on.It's in Easton Pa,probably 60 miles,and there's a HUGE gun shop 3 miles away,[SARCO] that I go to anyway to buy parts.I just wait till I need stuff from both before I go,LOL!!