Carl Hoffmeyer wrote:

Hi Pankaj,

The last time I did crystal grinding (which is what you are
*really* doing, I used a very flat piece of 1/2" plate glass
for the surface. The agent (grinding compound) was jeweler's
rouge and a bit of distilled water as a vehicle.

We held the crystal with our fingers (in Platex gloves) and
took a few very measured circular passes. We counted the revs.
A wonderful ham we knew (Mr. Irvine), designed and built a very
neat tester/oscillator to judge the results before sticking the
futtering FT-243 crystal holder all back together.

It consisted of wide respsonse oscillator using a computer
switching transistor (2N706 or thereabouts), a *very* thin
copper wire soldered to a small brass flathead woodscrew. The top
of the screw was polished down and could be lifted and placed
anywhere on the surface of the rock ... errh ... crystal.

The crystal sat on a polished brass flat (an old brass gear).
The gear and the wood screw served as the two contacts for
the rock.

I suspect that your "Flat lapping machine" may be taking too much
off the blank. Go easy with it. We also fooled around with HcFl
- hydroflouric acid - VERY bad stuff to play with - grinding your
rock is much safer.

Good luck.

Carl - in another life WB2YHE

wrote in message
oups.com...

Hello Group


I have a Flat lapping machine with me and have been trying to lap some
quartz blanks but after lapping when i measure the frequency I found
that the frequency spread is too high all the time, Can someone give
me some expert comments on how can I decrease the frequency spread.
Also I will highly appreciate if someone can please provide me links
to some helpful documents about flat lapping and some Do's and Don't
to improve the quality of my workpieces.


Thanks in Advances
Pankaj Trivedi.




Are you doing this for a few amatuer crystals, or is it for production?
What kind of reliability do you want?

My understanding of short-run crystal manufacture is you calibrate the
machine for how much it'll change the frequency per pass (or whatever),
you measure the frequency of a part-way-done blank, then you take off a
controlled amount from the blank.

AFAIK crystals need to be etched a bit if you want them to be resistant
to frequency changes as they age. Time-controlled etching is also a
good way to take off a controlled amount of material. But HF acid is
nasty stuff, so I wouldn't play with it unless you're in it for money.

--
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com