The original clear plastic...
The original clear plastic emblem off the '51 Ford trunk was in bad shape, and would take quite a bit of work to make it usable. The backside, however, is in good shape, making it an excellent part to cast.
Innovation is what sets real showstopping rods apart from the rest of the field, but it doesn't have to be big and elaborate to make a difference. In fact, small details usually make more of an impact. While a lot of rodders think being innovative and,coming up with something really different or unique requires a big budget and lots of expensive tools, such is not always the case. This is one of those situations.
It's called polyurethane casting and it's much easier than it sounds. The process starts with a solid part, anything three-dimensional. A Rhodia V330 silicone rubber mold is formed around the original piece; once the silicone cures, the original part is removed, leaving a reverse impression. This mold can then be used to cast with a variety of materials.
One type of material is Freeman's FMSC 1080 clear elastomer polyurethane (that's a long way of saying clear plastic). The coolest part about this plastic is that it can be tinted with special dyes available in many colors.
To demonstrate this process, we're using a trunk badge from a '51 Ford custom to cast a new one, which will become a third brake light. The original piece is weathered, cracked, and has been painted over, but that doesn't matter for this particular project because this emblem is a reverse image. That means that the lettering and crest is on the backside, visible through the clear front-an excellent example of what can be done with polyurethane casting.
A few tidbits of information are very important before starting a project like this.
First, the part to be cast must be super clean; any imperfections will show up, including minute little weather cracks.
The casting box should be clean and nonporous. A wood substitute like MdF (medium-density fiberboard) is great for building custom-sized casting boxes, but it must be sealed and waxed or the silicone will bond and the frame will stay put.
The casting shown here is called simple mass casting, meaning the part is solid and has a single flat section that will be open, such as an emblem. Complex casting is more complicated, requiring a parting line and two or more casting boxes. With practice, complex casting can yield some really cool stuff. For more information on that, visit www. freemanmanufacturingandsupply.com.
Careful attention must be paid to negatives. A negative is an area with a back cut; these areas can cause real problems when releasing from the mold; small negatives can work since the silicone is very flexible, but too big and the part will be locked in.
Other than that, polyurethane casting is really simple and a great way to add some unique aspects to any rod. Follow along and see just how to cast it yourself.
This Plast-Econ modeling clay...
This Plast-Econ modeling clay will be smeared in small amounts on the edges of the emblem. When the emblem is pressed in to the casting box, the clay squeezes out, creating a tight seal so the silicone does not flow underneath the part.
A plastic tray is used for...
A plastic tray is used for this casting. The silicone will easily slide out, and doesn't need any sealing or waxing. The floor of the tray has been lined with 1/4-inch sheet wax.
Once thoroughly mixed, the...
Once thoroughly mixed, the silicone is poured into the casting box. Note how the material is first slowly poured into the recesses of the emblem, where the air can become trapped.
The silicone requires a 24-hour...
The silicone requires a 24-hour cure time. Once cured, the rubber mold is removed using a flat blade to pry up the edge. The rest of the mold is then slowly pulled out of the box. The emblem, which stayed in the mold, is then carefully removed.
The Rhodia V330 silicone rubber...
The Rhodia V330 silicone rubber is mixed using a 10:1 ratio of base to hardener. The base is first measured out on a scale, and then the hardener is added.
Notice the extensive detailing...
Notice the extensive detailing of the part. Even with the careful pour, a few air pockets created minor defects in two of the five round dots (arrows).
The FMSC 1090 Fast Cast polyurethane...
The FMSC 1090 Fast Cast polyurethane plastic is mixed 1:1 by volume in a small mixing cup.
The plastic is tinted with...
The plastic is tinted with red dye formulated especially for this material. A single drop is all that is needed.
The surface will gather bubbles...
The surface will gather bubbles formed in the mixing process. A razorblade easily pops them, yielding a smooth, glossy surface.
The deep dark red plastic...
The deep dark red plastic is slowly poured into the casting to avoid trapping air in the pockets in the part.
Once cured, the part pops...
Once cured, the part pops right out of the mold. The silicone is extremely flexible, and can be used more than 100 times if you're careful.
The emblem is reassembled...
The emblem is reassembled with the metal bezel to test the fit.
Here's the new lens with a...
Here's the new lens with a little light showing through it. The housing will eventually be smoothed and painted with Mirra-Chrome paint. Now all we need to do is build the bulb housing to go behind it.
The newly cast part shows...
The newly cast part shows all the imperfections of the original part; note the weather cracks on the right side.