CDROM metal stripper

Why not just leave the metal on there and accept a very slightly lower capacitance ratio? You aren't using the thick polycarbonate as the dielectric anyway.

This will result in a parallel capacitance on the order of

Cpar = Cmax*thickness(mylar film)/(2*thickness(CD)). Since the mylar is probably 1 mil or thereabouts, and the discs are about 50 mils thick, this would degrade your Cmax/Cmin ratio to--well, about 100:1. Not too bad. I get about 1250 pF Cmax and 13 pF min with 1 mil dielectric, with epsilon=4. There's the self-capacitance of the plate to worry about too, which (in pF) is on the order of its diameter in centimetres, but that's about the same size as Cpar.

Cheers,

Phil

I just grabbed an old AOL one and stripped it in about a minute using a Bahco stripper, basically a TC blade in a handle. You attack the painted side. The trick is to bend the bend the CD ever so slightly over something large (I used a bench vice) so as to present a slightly curved face to the scraper blade.

Barry

I concluded the same--written up and illustrated with beautiful ASCII art last night--but I calculate double the parasitic due to additional shunt paths. Namely, fully unmeshed, the two shunt paths are via each plate to the metallization on its substrate CD, across the metallization, then across the CD+center dielectric thicknesses, to the other plate.

This results in four roughly equal-valued stray capacitors in series- parallel, with a net value equal Cstray(unmeshed) = Cmeshed * (central dielectric thickness / CDROM thickness) (assuming equal dielectric constants, which appears nearly to be the case).

That is, the variable cap's capacitance ratio is approximately the thickness ratio between the CDROM and the mylar dielectric. For a larger ratio, use a thinner dielectric.

Homer's sliding tubes suggestion is attractive, but Barry Lennox's stripping technique suggests another possibility:

Why not use Barry's technique to strip half the metal off each of two CDROMs, then glue brass (or aluminum foil) plates on top of the remaining metallized area (rendering it moot), and assemble the CDROMs with metal-sides inward, separated by your mylar dielectric?

Cheers, James Arthur

I read a reasonable 780pF with the whole assembly jacked tight together. Used a Polyethylene seperator, 3mil (er 2.3 ?). Plates made of tinned steel sheet 8mil, 0.2mm. "Glue" was double sided tape at