Mirror Drum
Over the last few years I have attempted to make several mirror drums. All were intended to go into working machines but, until now, none have made it to completion. This page documents the design progression. They all follow the general process outlined by Dave Gentle in his article describing his homemade mirror drum in the NBTVA Newsletter, Vol. 34 No. 3.
Version 1:
This is the most simplistic of my attempts, done with tin snips and an old paper cutter. It's more or less an exact copy of Dave's technique. The center support disc (the aluminum circle that the mirror clips attach to) is made from a single layer of .020" aluminum sheet, so needless to say it's more than a little wobbly. To make the support disc, a paper guide pattern marking the location of both the mounting and alignment holes (the outer and inner rings, respectively) was generated on a computer, printed, stuck to the disc with adhesive spray, then drilled with an ordinary drill bit. Pre-cut 1" x 1/2" back-silvered glass craft mirrors were purchased from eBay. They were secured to the aluminum clips with 1/2" x 1/2" Scotch Permanent Mounting Squares. It was purposely designed to be light weight so it could be direct-driven from a VCR transport motor. Due to it's flimsiness, though, it's more useful as a visual example than a usable device.
Version 2:
My next attempt fixed the problem of flimsiness by replacing the hand-cut .020" support disc with a much sturdier 1/8" aluminum plate. The rest of the design elements remained the same, except, due to the thickness of the plate, the mirror clips were positioned on the same side of the disc instead of one on each side. This one was intended to mount to a VCR head drum turned down on a lathe and belt-driven by an external motor.
Version 3:
By this point I had access to a Waterjet cutter capable of handling thin aluminum sheets, so I moved the design process fully into the digital realm. By arraying circles around a center point, an extremely accurate support disc could be made. One problem I ran into was that the Waterjet was not set up to use any type of abrasive for cutting, and therefore could only barely handle blasting through even the .020" sheet. To compensate for this, I designed several patterns that would be bolted together as layers, effectively increasing the thickness of the support disc.