Re: 1948 Packard interior plastics

Posted by HH56 On 2022/11/6 10:27:42
Another option would be to make a silicone mold and use a casting urethane. Since interiors can get rather hot if the car is standing in the sun use a material with one of the higher temp before it will deform ratings to cast the knob. There are also some casting epoxy materials that will withstand even higher temperatures but that is probably overkill. Smooth-On and others have several options.

For a finish, I don't think paint on casting material or fiberglass would match the original look very well so to my mind, the hardest part would be to match the knob color in the casting material. For that, it will take experimenting, patience, a good eye and being able to duplicate the formula more than once. With my castings, I found I lack some of those qualities but the Yesterdays Radio knobs (now made by Lavine Reproductions) have that part down to almost perfection. Before going to a lot of effort or expense maybe it would be worth touching bases with Lavine to see if those knobs are something they would be interested in doing.

As far as being molded onto the shaft, when Yesterdays Radio made knobs to replace molded originals a simple hole was drilled or maybe cast in the new knob. The knobs were then fastened onto the old shafts using epoxy. Most of the shafts have some kind of knurling or serrations the original plastic grabbed or formed around and if some provisions are made in the replacement knob hole for the epoxy to fill and harden into, it will hold satisfactorily. On a couple of knobs I replaced with repros I used a Dremel tool to make a couple of undercut or angled notches going into the straight sided hole to provide a space the epoxy could key into. With the angle wider at the inside it also made it harder for the knobs to be pulled off.

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