In article .com,
wrote:
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,


I'm not sure that this is the correct newsgroup for this
question -- though I'm not sure that one exists.

From your question, I'm presuming that you are attempting to
make frequency controlling crystals, not optical flats or some of the
other possible products which might be made by lapping quartz.

I've never done it, but I would expect that flatness (on both
side) is not the only important criterion. I suspect that the two
surfaces must be very parallel as well. Have you tried measuring the
thickness at all four corners -- and in the center? And you may need a
something with more resolution than a micrometer capable of reading down
to 0.0001" (or even 0.001mm)

Also, it may depend on how the crystals are mounted. I know
that really old ones in my collection are mounted between two plates of
metal so designed that they contact the crystal only at the corners. I
have seen others were the crystal was apparently vacuum plated with
metal on both sides (and perhaps the edges were ground free, as these
were round), with wires bonded to the center on each side.

I also believe that I remember that the orientation of the blank
relative to the original quartz crystal changes the behavior -- one
orientation may give a lower frequency, another may give a narrower
response curve, and a third orientation may give a lower temperature
coefficient relative to the frequency.

But -- this is really faded memory of something read over forty
years ago.

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.

Just some thoughts, and a lack of hard information.


Thanks in Advances
Pankaj Trivedi.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---