I use the OMOO silicon and smooth cast 300 resin for my parts, they are usually only slightly pliable when they first come out and within half an hour of casting they should be quite rigid. Is your mix a proper 1:1 ratio? If that's off it might be causing them to cure much slower which could account for the pliablity.
Micromark.com has a really good resin but it's slightly more exspensive.
The differance between how the pressure system and vaccum system works is that the pressure system crushes the bubbles down to a tiny size and at the same time it alter the viscosity characteristic of the resin which helps the bubbles flow up and out of the mold. It's not perfect and you still need well placed vents for the air and resin to escape from in order to get a good cast.
With Vaccum it sucks the air out of the mold literally, allowing the former air pockets to be filled completely with resin. It also helps suck the air bubbles out of the resin. You don't need as many vents on molds that are going to be used in a vaccum system as each part only needs one sprue connection, where pressure parts need at least two or more sprue connections.
Using either system will probably help get clean casts that are free of bubbles, another trick to try is applying baby powder to the mold and then shaking it off so only a very light dusting remians, this will usually help break up bubbles.
It's possible to combine both systems to get maximum effect, do the vaccum first and then pressurize second. But that's probably overkill for what most people will need. It also requires a resin with a slightly longer pot life so that you have time to get a proper vaccum and additional time for the pressure to be applied.
The air compressor and pressure pot are two completely seperate items. (you'll need both for a pressure system)
The pressure pot is a heavy duty metal pot that has screw down clamps and a rubber seal on the iside of the lid. You can place pobjects inside bolt the lid on and feed compressed air into it via hoses.
This is what I use (removing the spray gun and extra hoses)
They sell this same item on ebay slightly cheaper.
http://www.tcpglobal.com/spraygundepot/ ... TCP+PT8312Air compressors have a built in tank that stores the compressed air which is why they have a volume listed. (you can't open or close the tank as it's sealed) The larger the air tank the larger it's volume is, basically what that lets you do is fill more space or use an air tool longer before the compressor has to turn on again. If you are using a 2.5 gallon pressure pot then you will want a compressor with at least a 4 gallon capacity, that will let you pressurize the tank very quickly. I use a 6 gallon compressor and it takes me 5-10 seconds for my tank to pressurize to 42 PSI.
If I used a smaller tank, say 2 gallons it doesn't hold enough air to completely fill my 2.5 gallon tank so that means that the compressor engine will kick on and take a minute or two to get to the proper pressure level. The engine will run more often and it'll take longer to get things to the correct level.
In short you want a compressor that is at least a 4 gallon capacity, if there's not a huge price gap I'd suggest a 6 gallon one.
Here's the compressor that I use, picked it up at home depot:
http://www.homedepot.com/h_d1/N-5yc1vZ5 ... ogId=10053If you are on a tight budget this one will also work well:
http://www.homedepot.com/h_d1/N-5yc1vZ5 ... ogId=10053There's only a price differance of about $40, and honestly it's worth it to get the larger 6-gallon tank. It'll pressurize faster and run less often which is very helpfull as they are nosiy.
Horsepower isn't really that important for casting so long as you have a proper size capacity, a 1.5 HP will take longer to fill up the tank than a 2 HP compressor, but since you will want to be using a completely filled compressor tank each time it won't really matter how long it takes to get to that pressure level.
The compressor volume has a huge impact on getting things pressurized quickly and trying to beat the pot life of the resin.
The smoothcast 300 resin has a pot life of 3 minutes so you have to work fast, before you even start mixing make sure to have the molds sealed up and ready to go. Have the compressor charged to a proper level, and use quick release fitting for the hose connections so they can be popped on and off rather than having to mess around with thread fittings.
Mixing should only take 10 seconds which gives you about a minute and a half to get the pouring done and get the tank sealed. You have to work quickly and it's something you'll get used to with practice.
The smoothcast-305 has a pot life of about 7 minutes so it gives you a bit more time, the downside is that it takes twice as long to cure so it'll take 60 minutes rather than the 30m inutes to cure like the 300 does. Another trick that can be done is to refigerate the resin as the curing process needs heat. If the resin is chilled it'll set up slower giving you slightly more pot life time, but it also lengthens the curing time as well.
How you posistion your part can have a big impact on how and where the bubbles gather, never palce a part so it's completely horizontal as that will tend to trap air. Always give the part a slight upwards angle on one side if possible that way the air will flow up and out.
From the tutorial section:
viewtopic.php?f=3&t=80"The position of the parts is also important as it will help control where air pools and collects, causing trap points which results in bubbles in the part. Air will always rise to the highest point in the cavity; this is where you will want to attach the vent channels so that the air will leave through the channel rather than being trapped in the cavity. Also it is generally a good idea to place the wider or thicker points of the model at the bottom as it'll force the air up into the thinner area where you'll only need a single vent rather than 2 or more that a wide piece would need.
Here's another example:
On each of the parts air will rise to the top and trap in the upper surface of the cavity, so we attach vent channels to those areas. On the left and rightmost triangles all of the air rises up into the upper tip and then out through the vent. The middle triangle however has a large flat edge at the top of the piece which can cause air to trap all along that edge, you can add a vent at each corner but air may still trap in the middle of that edge, so you want to avoid positioning parts like that. By paying attention to the angles and position of the piece you can save a lot of headache over trapped air bubbles."