Michael Black wrote:
On Thu, 10 Jul 2008, Scott Dorsey wrote:

Otherwise you can get junk crystals at a hamfest and recut them for
whatever frequencies you want, but it's a pain.

Except they aren't in a holder that can be opened by unscrewing them.
Few are likely to tackle sealed crystals, too much trouble to open (and
then close afterwards) and of course the crystal blank is not held in
place with pressure, so that's even more work.

I did hundreds of those things when I was a kid, peeling open the crimp
on the bottom of the case, and lapping them down in the sink.

ANd of course, you never could grind a crystal to just any frequency,
at least not at home. You could open up crystal holders held together
with screws and grind the blank a tad (or add a bit of lead from a pencil
to lower the frequency) but you had to start with a crystal on a frequency
quite close to what you needed, and this only allowed an incremental
change. Move it too much, and the person at home couldn't do it evenly
enough.

I started out using Ajax cleanser and my finger, which does not allow much
change... you can go up a little bit but as you note it becomes difficult
to keep the sides parallel.

I wound up using pieces of window glass, with the blank sandwiched between
them, and with lapping compound from the auto parts store. The window
glass etches away faster than the crystal, but by holding the two sheets
together you can get remarkably parallel faces on the crystal and you can
move 500 KHz or more.

Incidentally I destroyed the finish on the bathroom sink in the process,
with stray lapping compound, and my mother still has not forgiven me.
I will say that I am much older now, and nowhere near as impoverished,
and if I need a crystal today I pick up the phone and call ICM.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."