Plastic Memories and Dreams
I do some very simple one part mold casting of wheels, hubcaps and some smaller parts like carbs. valve covers, heads and intakes.
The masters that I cast from come from various sources, kit parts that I or some of my friends have. From old promos or even some old toy parts. I am fortunate to have friends that have large collections of built kits, unbuilt kits, promos and parts bins. Two friends that I have in the model club that I belong to have been into cars and model cars for over 40 years and have been smart enough to keep all the cars and pieces. They have some unbelievable items.
The casting process is fairly simple and consist of two steps. 1) make a mold and 2)cast a part. I currently only do one part molds casting. This is done by pouring RTV rubber over a master part to create a mold and then pouring liquid resin into the mold to create the part.
Here are the steps that I use to make the mold.
I cast on a piece of glass, but you can cast on any flat surface. I place a piece of double sided carpet tape on the glass to hold the master and the containment wall in place.
|Here is a piece of flat glass with the double side
tape applied. The master part has also been stuck on the tape.
Note for this casting process it is best if backs of the master part
is flat. The parts do not all have to be flat. The
intakes I cast are not completely flat and they require a little
clean up to get the excess resin off of the finish cast.
If the master is chrome you will get the best mold if you strip the chrome before creating the mold, but you do not have to strip the chrome. For some of the parts I borrow I can not strip the chrome. In most cases I can make a decent mold and the chrome on the master is not harmed, but caution I have on occasion had the chrome removed by the RTV while making the mold. This is not good if you have borrowed the part to cast from a friend.
For some promo wheels that have a large axle stem on the back I have just cut the stem off to flatten the back.
|Once the master is stuck to the tape you will need to construct
a containment around the part to hold in the liquid RTV rubber when
it is poured. Here my containment is a section of an old pill
bottle. I have also placed modeling clay around the base of
the containment to seal it. You want a good seal or the RTV
will leak out.
Containments can be made out of many things and can be any shape. In this example I only have a single master wheel, but I have made larger mold that contain 4-6 wheels.
|Here I have poured the liquid RTV rubber into the containment to cover the master part. Pour slowly to avoid trapped air bubbles in your mold. I sometimes use a toothpick to lightly stir the liquid around the part. Be careful not to knock the master part loose. The RTV that I use takes about 8 hours to fully cure into a mold for casting resin.|
|After the RTV has cured remove the solid RTV from the glass and the containment. Remove the master part and you know have a mold for casting resin parts. Mix the resin and pour it slowly into the mold. Try not to overfill the mold with resin and you will avoid a lot of sanding on the back of the cast item. The resin I use has a cure time of 8 minutes, but I usually wait 12-15 minutes until the cast part is hard. Be careful if you remove the part while it is soft. You can distort the part.|
My cast wheels are always flat on the back. But with a little 5 minute epoxy you can get them to fit anything. I also cast wheel back in this same process. I usually plug the axle hole in the wheel back of the master with a small piece of clay. Then as I use the cast wheel back I drill the size axle hole I need to mount the wheel.
Hope this info is helpful.
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