Products used in this How To:

• Original Car Body
• M-2 Silicone Rubber
• Alumilite Regular
• Alumilite Synthetic Clay
• Rubber to Rubber Mold Release
• Excel Knife
• Corrugated Plastic
• Sand Paper
• Popsicle Stick
• Cups

Molding & Casting Slot Car

This How To process will walk you through step by step the procedure for making a two piece squish mold and casting a slot car.


This is an HO scale slot car body we wish to reproduce.


First and foremost it is important to have your original perfect. Sand out any imperfections, scratches, or flaws with a light sand paper or steel wool. If you wish your parts to be high gloss, make sure your original has your desired surface before making the mold. The mold material will pick up every detail including stickers, decals, etchings, and scratches that will show up in every part you cast.


Once you have the original perfect, decide what material you are going to use for your mold box. You can use styrene, corrugated plastic, wood, metal, foamcore, posterboard (shiny side), or any other non-porous material. Here we chose to use styrene for the base and corrugated plastic for the side walls of the mold box.


Using Alumilite's Synthetic Modeling Clay we filled in the car body with clay to act as one half of the mold. This prevents the mold making silicone from flowing inside the car and removes any undercuts. We will use the bottom edge of the car as the parting line.


Once we've clayed in the inside of the body, we carefully clean off any excess clay that filled in any of the detail on the outside of the car body. (Take the time to clean off all the clay out of the detail - this will allow you to make a flawless mold that picks up all of the detail from your original)


Place the clayed up car body on a bed of clay. This will act as the base for the second half of the mold that will be squished into the mold of the outside of the car body.


Once the car as been competely clayed up, assemble and seal the mold box using the same modeling clay, hot melt glue, super glue, or any other sealing material.


You are now ready to mix and pour the first half of your silicone mold. We used Dow Corning's M-2 silicone mold making rubber in this instance because that is what we had readily available at the time. I would probably suggest using Dow Corning's HS II for this application due to it's better tear strength and softer durometer. It is also much easier to use due to it's low viscosity. The HS II is also available in 1 lb kits where the M-2 is not.


Once the silicone is mixed completely, pour it slowly into the mold box from one corner. Let the silicone flow around the master naturally. Avoid pouring the silicone directly over the master to reduce the chance of trapping air pockets against your original.


Let the silicone set up over night.


Demold the first half (completly remove all the clay), apply a rubber to rubber mold release (you could also use a thin layer of Vaseline), mix the second batch of silicone, and pour the second half of the mold.


Allow the second batch of mold rubber to set up overnight. Remove the mold box and separate the mold. Then simply remove your original.


You are now ready to cast your first slot car body. Mix equal amounts of Alumilite Regular into a paper cup. (Remember to always preheat your mold in a microwave for a minute on high or in a conventional oven for 20-30 minutes at 140 prior to casting - this will help the thin sections set up properly) Also, make sure to shake the 'B' side if using Alumilite Regular before measuring.


Once the resin is mixed thoroughly, slowly pour the resin into the mold. Fill the cavity to the bottom of the car body.


Take the second half of the mold and slowly lay it into the first cavity to squish the excess out. You can see we also poked two holes in the top of our mold to help vent the two mounting stems on the inside of the car. You can do this by taking a small brass tube and twisting it up from the point in the mold where the two stems are located. This will allow the resin and any trapped air escape from that point.


Wait approximately 7-10 minutes to demold. You should be able to tell the resin is solidified from the excess that was squished out of the mold. If your parts are taking longer than 10 minutes to demold and/or if the parts are soft when demolding, try warming your mold up more prior to casting.


Separate the two halves of the mold to remove your cast piece.


Remove your cast piece and trim the flash off with an Exacto or Excell knife.


You now have an exact replica of your original slot car body.