Molding Plastic

This plastic molding project started when I could not find a plastic toroid (i.e., a hollow donut-shape) part I needed for one of my new projects. First, I needed to build a mold. I used my lathe and my lathe duplicator to build the mold's inside and outside pieces.

This video shows turning the inside mold piece and cutting out the outside mold piece. I used white oak for both mold pieces. The outside edge of the mold is 10 inches in diameter. The mold is built to produce half a toroid that is 1 inch in diameter.

Next, I molded a plastic test strip to get an idea of the heating time, temperature, and pressure needed to make a plastic molded part. The plastic I used was purchased from Home Depot.

The pictures on the right show the complete mold and mold press I used to make the first test piece. This test piece taught me that I did not heat the plastic long enough. Two of the test piece's edges cracked under the pressure of the mold press. I also learned that I would not need any kind of release agent applied to the mold because the plastic did not stick to the mold.
Test1 Test2

This part of the process involved preheating my barbeque grill to 300 degrees and then heating the plastic on the opposite side away from the direct flame. I used an aluminum cookie sheet and a piece of parchment paper to keep the plastic from sticking to the cookie sheet. I heated the 12 inch square piece of plastic at 300 degrees for 10 minutes until it became soft and malable.

Next, I slid the plastic sheet off the cookie sheet and pressed it with the mold. The video on the left shows this process.

The parchment paper and The 'Ove' Gloves are a helpful tip.

Finally, after waiting about 10 minutes to let the molded plastic cool, I removed the molded piece from the mold.

The video on the right shows the removal and completed formed piece of plastic.

I molded several of these plastic pieces. I put each molded piece in the bottom half of the mold and trimmed them using my router duplicator. I then attached two halves together to finish making the plastic toroid.
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