[JMS] How does one "grind a crystal" to change its frequency ?

[Joe Rubin]

Dear Sherrill, I used to "grind" crystals in the old days. An FT-243 can be 
taken apart by removing the face screws. Then the crystal blank is removed 
from the holder by slipping it out. The crystal is placed on a convenient 
plate glass square (about 4"x4") size irrelevant and a small amount fine of 
carborundum powder (you can use automobile valve grindind compound, the fine 
stuff only and 1/4" to 3/16"r the blank and usually rotated in a figure 
eight or so.  The idea iis to use very light pressure and keep the faces 
paralllel . A few 8 and the blank is washed very carefully , reassembled and 
tested on an oscillator or the intended xtal circuit. It is not a fool-proof 
method and often the thing will quit working a you cannot get it to 
oscillate again. The reasons vary but usually due to lack of parallism sm, 
or lack of cleanliness. The blank should be handed by the edges only. The 
crystal an only be moved so far (a few Kc) and if one is out of the amateur 
band I doubt it could be moved very far.
Crystals oscillate in the fundamental mode, that is if you have one for 
forty meters (7 mHz) it will oscillate there. An overtone crystals 
manufactured to perate in the second to fifth harmonic (7 x 2 = 14) (7 x 3 = 
21) ... of course there are special cases. The older Amateur Radio Handbooks 
used to have articles on this subject. I will try find some for you. The 
main thigs to remember are: paralellism, Cleanliness and a limit to the 
frequency excursion..  Let me know if you need more information or futher 
explanation.... 73  Joe  W4CBJ/WX4TRA.

>From: "Sherrill Watkins" <Sherrill.Watkins at dgs.virginia.gov>
>Reply-To: The James Millen Society Members Email Reflector 
><james_millen_society at mailman.qth.net>
>To: "The James Millen Society Members Email Reflector" 
><james_millen_society at mailman.qth.net>
>Subject: [JMS] How does one "grind a crystal" to change  its frequency ?
>Date: Thu, 31 May 2007 10:27:47 -0400
>
>Friends and Members of the James Millen Society: Please be advised that 
>from
>time to time, I see FT-243 crystals for sale in odd frequencies; i.e. that
>are outside of the amateur bands and of no use. Years ago, I heard that it
>was possible to "grind" a crystal to raise its frequency. Also, I heard 
>that
>one could "rub" a crystal with pensel graphite to lower its frequency.  
>Yet,
>I have never seen any article published in any major amateur publication
>including various handbooks, or magazines such as QST, Electric Radio, The
>Old Timers Bulletin, etc. as to how this process is be performed.  Can 
>anyone
>refer me to a good source or explain the process in great detail? Also, 
>what
>is meant by the term, "overtone" crystal? Thank you very much. - Sherrill 
>W.
>k4own, member
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