Here is my first attempt to hold thin aluminum in place so I could mill plates for my butterfly capacitor.
I purchased a small sheet of thin aluminum from Home Depot for around $13. The size of this sheet is 8” by 24”, with a thickness of 0.025”. This is just about the thinnest sheet aluminum available, unless you go looking for foil rather than sheet. However, as 25 thousands of an inch, it is thick enough to build a capacitor.
Since I designed each section of the capacitor (one rotor and two stator plates) to be cut out of a four square inch section of aluminum, this plate should be large enough to print 12 sections.
The first step was to make sure that the aluminum sheet was square to the CNC machine. I did this by resting a straight edge against two bolts inserted into the waste board, and then squaring the aluminum against this straight edge. (You might also notice that I have been printing plastic bolts, as shown above. They work fine!)
Plastic Clamps hold the Thin Aluminum Down
As shown above, I have 3D printed four heavy clamps in ABS plastic. These are held into the waste board using 1/4” carriage bolts and spinners with captive nuts. I put a piece of thin hardboard under the aluminum, and then clamped everything down. Attachment was quite secure. I could not move the aluminum by hand.
However, the one concern I had was the the thin aluminum sheet might lift slightly in the middle. This was especially so because my cutting tool is an “up cut” end mill. This is good for clearing away chips, but it also means that the cutting motion creates an upwards pull on the material. We will see how it goes when I do the cut.