[time-nuts] Grinding crystals...

Robert Darlington rdarlington at gmail.com
Fri Jun 21 16:59:57 UTC 2013


I used to produce ultrasound transducers using a very similar method.  I'd
continuously monitor the resonant frequency with a network analyzer as I'd
lay down gold/silver/whatever with an evaporator cup from both sides.   My
chamber has a shutter to cover the transducers (I think it has 12 or 15
stations around the circumference), but I could vary the current through
the tungsten heaters on a per transducer basis to taper off and stop the
deposition.

Every once in a while a customer wanted a 10.0000ish MHz transducer, and
all Panametrics (Olympus NDT) could crank out would be something kinda
sorta near 10MHz -like 9.85MHz.  As a lowly technician and not a scientist,
I don't understand why this mattered for the work they were doing, but the
national lab here in Los Alamos really seemed to like their matched, high
precision transducers.

-Bob


On Thu, Jun 20, 2013 at 5:57 PM, Gary <nuts at lazygranch.com> wrote:

> A common scheme in metal deposition measurement is to measure the
> frequency of a crystal prior to starting the deposition process, then
> monitoring the frequency shift of the crystal as the metal is sputtered.
>
> I was told crystals are tuned this way at the factory, but don't know this
> for a fact.
>
> "Burt I. Weiner" <biwa at att.net> wrote:
>
> >Brian,
> >
> >I remember grinding FT-243 crystals.  I had a TV set safety glass
> >about 18" square and about 1/4" thick.  That and some Comet type
> >cleanser mixed with water to make a thin paste would work wonders.  I
> >was taught to put my finger on the corners and grind an equal amount
> >on the 8 corners (4 on each side) so as not to remove the bevel of
> >the quartz.  Once I applied this lesson I was able to grind crystals
> >that were more stable and more active.  When I over-leaded them I was
> >generally able to remove the lead using alcohol.  I've still got the
> >old TV safety glass although it has an area near one corner that is
> >very opaque do to all the grinding that was done in that area.  Those
> >were fun days!
> >
> >Burt, K6OQK
> >
> >
> >>From: Brian Alsop <alsopb at nc.rr.com>
> >>
> >>Reminds me of the FT-243 xtal controlled transmitter Novice days.
> >Xtals
> >>of the frequency you wanted were hard to come by.  We would grind
> >xtals
> >>a bit on a bed of very fine abrasive to raise their frequency.
> >>
> >>The other trick was taking a pencil and adding graphite to the xtal
> >>faces to lower it's frequency.  You couldn't add too much or it would
> >>stop oscillating-- forever.  Never did understand the forever part.
> >>Removing the graphite didn't bring it back to life.
> >>
> >>Brian
> >>K3KO
> >
> >Burt I. Weiner Associates
> >Broadcast Technical Services
> >Glendale, California  U.S.A.
> >biwa at att.net
> >www.biwa.cc
> >K6OQK
> >
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