In the last installment, we learned the basics of casting terminology,as well as how to prepare a master, and make a simple mold. This time around we are actually going to make a detail part from the moldwe prepared.
As I have said before, I like the products available from MicroMark. While these do have some drawbacks (a tendency to soften anddeform in extreme heat) so it probably isn't the best to make truck sideframesthat are expected to bear weight in outside conditions during the summer,but for general detailing parts their CR-300 line is hard to beat. It is readily available, in sensible quantities, has a rapid demold timeand a decent pot life. You can even add pigment to it now to colorit a variety of colors. It also has no odor and is water thin. So basically keep it off you and your clothes and you should really nothave any problems with it.
Casting is an art form as well as a scientific procedure, so inorder to be successful you really have to be in the right frame of mind,and be willing to be patient, as well as really screw up a few times beforeyou get it just right.
First of all you need a clean well lit bench top to work on, youshould have room for all your supplies, as well as room to mix and pourresin. I like to put down a sheet of 8.5" x 11" card stock to protectthe work surface from dribbles and errant spills. Get out your suppliesincluding three plastic cups for mixing. If you think your goingto make more than one pour take a permanent marker and put an ‘A' on onecup and a ‘B' on the other. This will help you keep putting the rightmaterial in the right cup, and you can use the third one for mixing. If you are using a really intricate mold, a light coating of a releaseagent might be appropriate, but don't use so much that it would pool inthe bottom part of the mold and ruin your casting.
Dispense equal portions of the Parts A and B into the appropriatecup. It is really hard to mix a small amount of resin, so I eitherwork with a fairly largish part, or have several molds ready to pour. It is easier to mix some more resin later than to let it go to waste, sobe a little conservative in your estimates.
After pouring parts A and B into the third cup, mix thoroughly, butavoid splashing the raw resin around. I generally hold my littlefinger under the bottom of the cup while I'm doing this. As the resinbegins its chemical reaction, it produces an exothermic reaction, thatis it starts to heat up.
When I can feel the bottom of the cup start to get warm, its time topour. The same procedure that applies to pouring RTV can be appliedto the actual resin itself. Pour from the edge and allow the resinto fill the mold, flowing into all the nooks an crannies. In someplaces you might have to take a sequin pin and work the bubble out of partsof the mold.
Once the mold is filled, sit back and watch as some interesting thingsstart to happen. First of all the mold will get warm from the chemicalreaction, hopefully all the major bubbles will work themselves to the surfaceon their own. Then you should notice small white tendrils snakingtheir way through the resin mixture.
Then a core of white material forms in the thickest part of the mold,then finally the whole mold is filled with solid white. Read theinstructions that come with the resin to determine the appropriate amountof time before you demold the part, generally about 10 minutes, with theresin reaching full hardness in a couple of hours. After its fullyhardened you can pull the part out of the mold and admire your handy work!
You might notice that the back of your casting is not completely flat. There are a couple of things you can do about it. One is to simplyuse a belt sander to grind it flat, or you can cover the top of the moldduring the casting process. If I want a flat piece uniformlyI will generally cover the top of the mold with a scrap piece of styreneand weight it down with a spare locomotive weight
Now you can turn out some simple parts on your own. Rememberlike any other new skill there is a learning curve involved so don't getfrustrated if you mess up a few times. Just toss the results, andtry again, success comes with practice!
In our next installment we're gonna get into some of themore intricate aspects of casting with resin, including using two partmolds.
Until next time.........