Slowly but surely I have been milling butterfly capacitor plates on my Mostly Printed CNC. 

I have now produced enough sections to start putting together a finished product with my butterfly capacitor plates. The next step is to 3D print some capacitor end plates, and by some brass threaded rod and nuts to hold all the pieces together. My plan is to put together a three section capacitor and then measure the results. This will give me a good idea as to whether or not my results match what the formulas predict. I can then mill and add more sections to get the range of capacitance that I need for my loop antenna.

While this testing is underway, the motorized remote control for the variable capacitor will be prototyped. I am going to use an Arduino driving a small stepper motor for the rotation, together with some worm gears that I plan to 3D print.

Butterfly Capacitor Plates are not easy to cut

The big challenge in CNC milling these aluminum plates remains getting them to sit flat and level on the machine table. I am still using blue painters tape to hold down the material. Two strips of painters tape are glued together to hold everything in place. I have switched from Super Glue to multipurpose spray adhesive – 3M Super 77. A short blast of of Super 77 on one side provides great adhesion.

But I still have too much variability across the surface to get a good clean cut. I am going to try something different for the next batch of plates. Also, if I do a second capacitor, I may switch to 0.040” aluminum sheet which should be less prone to lifting while being milled.

In the meantime, a good vice and file is going to be needed to trim any sharp edges off these plates. I hope my friend will let me use his vice with rubber-faced jaw caps so that I can avoid any damage to the aluminum. I will also need to remove some bits of adhesive from the plates with acetone.