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

[john]

Just a question (and perhaps indicates why I have not been real successful 
at moving a crystal very far before activity falls off)... how do you 
"figure 8" the thing, without touching it ? They're such small slivers of 
quartz, it's really hard to handle it. I suppose rubber gloves could be 
used, and only use tweezers to lift it.  Cleaning it I guess could be done 
in an ultrasonic cleaner.

The "ancient ones" had a good process, that is not obvious....or....they 
too ruined a lot of blanks!

John K5MO




At 06:32 PM 5/31/2007, Joe Rubin wrote:
>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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