by paulson games » Wed Aug 18, 2010 4:52 pm
Legos work great, best source for them is to order the bricks from lego online as most of the kits in the stores don't have many of the long straight pieces. I ordered up a bunch of them ranging from 1x2 all the way up to 1x16, I absolutely love using them for the boxes.
One thing you may notice is that the legos will loosen up over time so if you make regular use of a certain mold pattern you can always glue the pieces together to make them a bit more permanant. I also sometimes tape the outer face of the walls to help hold everything together tight. If you tape the molds make sure it stays under pressure the entire time because air traps inside the lego part and if it's epressurized before the silicon fully cures it can burb air out and cause cavities in the silicon. (The tape keeps the air from escaping outwards as easily and instead it goes into the silicon) However it won't be an issue if you leave it under pressure the entire cure time.
For sealing up the underside I cut pieces of sheet styrene to the correct size and then scotch tape them to the bottom. Most of the boxes that I use are a fairly uniform shape and size so I can reuse the stryrene pieces over and over. A good source of cheap styrene is buying "for sale" signs at the hardware store, I've found that the local home depot carries it much cheaper than the hobby shop. For a thicker styrene source you can also use the huge sheets of lighting panel plastic.
Most of the paint pots converted into a pressure pot have a round bottom to fix this I picked up a cheap baking pan that was a close fit, I had to bend the lip upwards with a pair of pliers so it'd fit but it give me a nice smooth level surface for placing molds on and the non stick coating helps if you have overspill as the resin flakes right off. I placed a bunch of sand in a bag under the pan that way it filled up most of the excess volume, with less physical volume to fill the pot pressurizes much faster and the air compressor does less work.
When I make my molds I keep them under pressure the entire cure time as the silicon is susceptable to bubbles. I've switched to using Smooth-On as their stuff is very good on price and the cure time on their silicon is just 70 minutes, although I usually let mine sit for a full 2 hours just to be safe.
Normally my resin takes about 30 minutes, they state that it's a 10 minute cure time and a 3 minutes pot life so in theory it should be finished in 15 min total. The problem is that their estimate is only good for large pieces which can heat up and cure faster, small thin parts take considerably more time as they don't generate as much heat. I've found that almost all of the parts I make take about half an hour.
I let the resin stay under pressure for at least 10 minutes as it's relatively solid at that point and can be removed without any left over the bubbles expanding. So figure out what your average cure time for the resin willbe and it should be ok to remove at about half of that time. Every brand of resin will have differant properties so what works for one brand may not carry through on others so it's always a process of experimenting.
I let mine stay under pressure for 10 minutes and then stand in the molds for another 20 before I remove the rubber bands.
It's also important not to let the resin sit in your molds too long, I forgot and left some parts in the mold overnight and the next morning it was like they were superglued in place and it tore the molds which were quite new, even with mold release it'll eventually bind up so make sure to always remove them within an hour or so of casting at the latest.
Last edited by
paulson games on Wed Aug 18, 2010 8:32 pm, edited 2 times in total.