Old Knobs With A Cast Of Thousands

You have an old radio — in the case of [The Radio Mechanic], a Stromberg Carlson — and it needs new knobs. What do you do? You can’t very well pop down to the local store and find any knobs anymore. Even if you are lucky enough to be around an electronics store, they aren’t going to have knobs to do justice to an antique radio. You could 3D print them, of course, but there are a number of issues with transferring the old knob to a CAD file for printing. So [The Radio Mechanic] decided to cast them instead.

He printed some fixtures to help with the molding using two-part molding silicone. He mounted the knob on a shaft in a jig, filled the jig with silicone, and lowered the knob into the mix. The next day, he had a good-looking mold.

The next step, of course, is to cast with resin. Admittedly 3D printing would have been faster, but would not have as nice a surface finish. The epoxy resin is clear, but he was hopeful that some caramel pigment would match the original knob color. Spoiler alert: it didn’t. The resulting knob looked translucent, like a root beer barrel candy, rather than the brown sugar color of the original knob.

The knob needed a spring insert to hold the shaft, so he repurposed some from a different kind of radio. Overall, this is the kind of thing we always think we are going to do when we need something and then we rarely follow through. Then again, we rarely have the patience to wait as long as these two knobs took to make.

Of course, a casting guerrilla doesn’t have to make just knobs. You can even add metal powders to do cold metal casting.

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Brass Hardware Makes For Pretty Potentiometer Knobs

Knobs and switches can make or break the aesthetic and tactile appeal of a project. Fine hi-fi hardware goes hard on these details, while cheap knock-off guitar pedals often go the other way. If you’re looking for a unique, cheap, and compelling solution for potentiometer knobs, you might like to consider using converted brass hardware for the job.

Gorgeous, no?

The idea comes from [Kevin Jordan], who realized that some simple 3D printed parts would enable him to repurpose brass hardware for use with common split-shaft potentiometers. He grabbed a bunch of brass flare caps intended for use with gas piping, and got to work.

The result is the simple 3D printed cap converter. It has a threaded outer portion, which screws neatly inside a brass flare cap. Inside, it features a hole to mate to the potentiometer shaft. While this could be done with a spline, it also works with a simple hole since the plastic is soft enough to simply push the potentiometer shaft into.

The flare caps look great when pressed into service as knobs. [Kevin] uses them on a tennis racket guitar he built, and the brass knobs beautifully set off against the natural wood finishes of the build. If you’re looking for some unique adornments for your own projects, you might like to experiment with this concept yourself! Alternatively, you can try making your own knobs from scratch.

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A Great Way To Make Quick And Easy Knobs

Here’s a great way to quickly and easily make attractive and functional knobs¬†with no tools required. All you need is some casting resin (epoxy would do in a pinch), a silicone mold intended for candy, and some socket head bolts. With the right preparation and a bit of careful placement and attention, smooth and functional knob ends are only minutes away. Embedded below is a short video demonstrating the process.

These may not replace purpose-made knobs for final products, but for prototypes or to use around the shop on jigs, clamps, or furniture they certainly fit the bill. With a layer of adhesive fabric or rubber, they might even make serviceable adjustable feet for low-stress loads.

This technique could be extended to reproducing broken or missing dakaware or bakelite knobs. This, of course, would require an original, unbroken knob and a small silicone mold, but it’s still a project that’s well within the capabilities of the garage-bound hacker.

While we’re on the subject of knobs, don’t forget we’ve seen an excellent method of repairing knobs as well.

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