Product Review of Alumilite Urethane Molding Materials.

We were quite interested in trying out Alumilite's urethane molding materials, and for a variety of reasons. First, it's something we've never done, so the opportunity to learn a new skill couldn't be passed up. Second, we were curious about the quality of the finished product and its cost. In addition, we were curious about how hard it might be to learn the fundamentals of casting plastic parts. We learned a lot.

This photo shows the products Aluminite sent us.

The materials came with a DVD showing many different molding/casting techniques and considerations. It gave a lot of helpful tips and explained the intricacies of the process. After viewing the DVD we went on our long-awaited vacation. When we returned we set about casting a replacement tail light lens for our old Ford truck.

The first thing we did was to clean up our original taillight lens.

Our first attempt at this process involved creating a two-part mold. That is, we were casting a new tail light lens that had a smooth, curved outer surface and a multi-faceted inner surface. That meant we had to cast one side of the mold and then wait 24 hours for the rubber to cure before casting the reverse side.

The first step is to build a form used to create the mold. The Alumilite folks place a lot of emphasis on using modeling clay and either plastic or aluminum to help create forms, and we have to agree (in retrospect) that it's the best technique. However, we decided to create our form from cardboard and metal duct tape, two materials hobbyists are more likely to have on hand. We made our form about ½ inch larger than the lens and deep enough to create the rubber mold.

We drew guidelines about 1/4 inch from the sides of the lens.

We built our form from 2 inch strips of cardboard.

We mixed the two components of the rubber compound.

Then poured the rubber compound into our form.

Oops!

We knew that we had to create "register pins" in the mold so the mold halves could be perfectly aligned. We recalled that the DVD showed using a pencil eraser to create indents into the clay to create the register pins. Clay? What clay? That's when it came back to us that the DVD recommended that for a two piece mold, you embed the original object in clay, and pour the first half of the mold on top of the clay, remove the clay, turn it over and then pour the second half. Not only does this provide an easy way to create the register pins, it gives you control over the positioning of the original and the thickness of the mold. But the rubber compound was mixed and there was no turning back.

We pressed our lens into the rubber compound and created our register pins using short pieces of aluminum rod. We noticed that the lens had a tendency to float on top of the compound and added some weight to the lens to bring it back to the appropriate depth.

After realizing our error, we continued by pressing the lens into the rubber molding compound.

Tip #1: Be sure to become thoroughly familiar with all the steps involved in the process.

The lens tended to float on top of the rubber, so we added some weight to hold it into the mold.

After the bottom half of the mold cured, we poured the top. We didn't have quite enough molding rubber to properly cover the lens. (You can see the edge of the lens showing through the rubber). So we displaced the rubber in the center of the lens with the lid from the rubber compound. It was just enough to adequately cover the edge of the lens.

Once we had the mold split in two we were quite impressed with the level of detail that the RTV rubber maintained. It was at that time we discovered our lens poking through the rubber. In an attempt to repair the mold, we mixed a blob of Alumalite's Mold Putty - a fast-curing mold compound - and laid it over an area of the RTV that we cut out. It cured just fine but the Mold Putty didn't adhere to the poured rubber compound as well as we hoped. And because the mold in that area was thin and flimsy, it couldn't adequately support the additional weight of the putty.

You can see that the mold accurately conformed to the intricate shapes of the lens interior

We attempted to patch the mold using molding putty. Unfortunately, the patch didn't adhere to the mold very well.

Alumilite Product Review continued on Page 2