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

Thu May 31 21:26:41 EDT 2007

Hi Joe,

I was thinking about it. Wouldn't it be better to use two large pieces 
of glass, let say 1 sq ft? If you placed the crystal in the middle 
between the two large glass plates with your grinding solution then one 
glass could be moved in your figure-eight pattern. I would think that 
simply by the relative size of the glass plates to the small crystal it 
would maintain the parallelism.

I remember in my novice day guys would use regular kitchen Comet. I 
would think that whatever abrasive compound you would use that it should 
maintain an even grinding surface and that each grinding particle would 
be of relatively equal size. I could see goofing a crystal up really 
fast if you had more grinding material on one part of the crystal than 
on another part. You would have your non-parllelism simply due to the 
aforementioned. I wonder in this day of hightech composite materials if 
a solid material with a light oil on it surface could be used in place 
of one of the glass sheets. I bet a sheet of smooth carbon fiber is 
actually a good grinding surface for crystals. Now where did I put my 
stock of carbon fiber sheets, hi.

I wonder how they do this work today. I would think that crystal 
development has advanced a long way since the days when hams were doing 
this back in the 40's and 50's.

73

Don N9OO

Joe Rubin wrote:
> What you need is a small (1" x 1" piece of 1/4" or 3/16" PLATE glass. 
> You can get a piece from your local glass shop for nothing... I was 
> lucky, my father was in the glass business, HI. With this thickness 
> glass, you have some thing "to hold on to"... (the edges). Plate glass 
> is used for it's inability to "bend". The idea is to 'try; to get an 
> 'even' grind. If you use just your finger, you will put more pressure 
> on the center than the edges and ruin the parallelism. Yes, you can 
> ruin one easily without even trying hard... We used to wash the 
> blanks, holding them by the edges... and rubber gloves are a good 
> idea. The surface tension be=tween the small piece of glass and the 
> blank is 'supposed' to hold it... Never had any luck changing them 
> more than a few kilocycles, OOPS I mean a few kiloHertz. You can rinse 
> then off in tap water and then clean them with isopropyl alcohol.
> Tap water in some areas contain impurities and the slightest bit will 
> keep the thing from oscillating...that is why distilled water is 
> recommended. More info??? 73 Joe W4CBJ/WX4TRA.(Ancient One).
>
>
>> From: john <johnmb at nc.rr.com>
>> 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>,james_millen_society at mailman.qth.net 
>>
>> CC: Sherrill.Watkins at dgs.virginia.gov
>> Subject: RE: [JMS] How does one "grind a crystal" to change its 
>> frequency ?
>> Date: Thu, 31 May 2007 19:29:17 -0400
>>
>> 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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