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R/C Combat Vehicles

Track Pad Molding


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The following instructions for casting cleats into Intralox flush grid track were provided by Kent Massey at Chatten Associates . Kent designed these cleats to improve traction in rough terrain and to run quietly on hard smooth surfaces. These cleats use Mold Max 30 silicon mold material, PMC-790 urethane rubber, SuperSeal and Universal Mold Release available from Smooth-On . Trial size quantities for all four are sufficient. PMC-790 urethane rubber is about the same hardness as tire rubber. A vacuum bell jar is handy to get bubbles out of the silicon mold material but it is not absolutely necessary. You will want to find a source for 5cc syringe bodies. They are very useful for injecting urethane into the molds.
The cleat in this mold master was carved from bass wood, and screwed into the web of the track segment. The portion of the cleat that wraps around the web was made using Bondo. The whole thing was sealed with Smooth-On SuperSeal. Cut off the tracking tabs and the curved part of the hinge joints. Do not cut off any more than is required to get rid of the thicker curve portions.

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The first step in making the mold was to cut a piece of gaffer's tape or duct tape. Cut the tape so it will wrap around the mold master and just reach the top of the plastic.
Firmly seat the mold master, centered on the tape.

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Make four cuts and fold up the ends.
Fold up the long edges, pulling tight to prevent any bowing of the tape into the gaps of the mold master.

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Tear a one foot piece of tape in half lengthwise.
Wrap the tape around the sides of the mold master. Do not let the tape extend below the bottom of the mold master because you want the mold master to sit flat when you pour the silicon mold material. Spray the inside very lightly with mold release (too much mold release will cause the tape to separate from the plastic). Mix the silicon very thoroughly. Pour it in slowly at first, letting it flow into the voids. Continue to pour until the top of the mold master is covered about 3/8" deep.

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After the silicon dries, remove the tape. This is an example of a good silicon pour (blue) and a bad one (pink). The pink one still has the mold master embedded in the silicon. The reason that the pink one is bad is that it was poured too quickly and the silicon was near the end of its pot life. The silicon did not flow properly into the voids.
Gently cut the end pieces out and cut to expose the top of the web on the outside of the cleat.

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Remove the mold master and clean up the mold.
Once you have a good mold, mix the PMC-790 very thoroughly. Spritz the mold once with mold release. Be VERY light in your application of mold release when casting the urethane. Using too much mold release will cause the mold release to mix with the urethane and prevent a complete cure. Put a track segment into the mold, being careful not to get mold release on the surface of the plastic. A single 5cc syringe full should just about fill one mold. You can do about 20 molds at once, before running out of the pot life of the PMC-790. Then throw away the syringe -- there is no way to clean it.

After the urethane has hardened, you can GENTLY peel the mold away from the track. The mold has thin spots near the top of the track segment where it will tear if you move too quickly. Some excess urethane may need to be cleaned up. Then you need to cure the finished pieces in an oven at 175 degrees F for a couple of hours.

Our experience was that the entire casting/curing process for 20 tracks takes about five hours. You will need about 200 tracks, so allow time.