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Re: Crystal question

Alan Leech wrote:

> I heard that crystals are etched with some sort of acid, to change the 
> freq' upwards..  Dunno 'bout stability, though.. 

Oscillator crystals, made of quartz, can be etched using hydrofluoric 
acid (HF).  However, you do NOT want to do this.  HF is extremely nasty 
stuff, much worse than say, automobile battery acid.   Don't even think 
about it.

Most oscillator crystals are cut with a diamond saw along certain 
crystallographic planes, then ground to the correct thickness using 
abrasive powders.  This is very difficult to do.

You can sometimes "pull" a crystal a little bit (to a higher frequency) 
by grinding it yourself.  However, if you mistakenly grind one part more 
than another, so that the sides are not parallel, then it will stop 
oscillating.  You can also lower frequency a bit by rubbing a pencil on 
the side of the crystal (not the case, the crystal inside).  Also 
tricky, especially with modern small crystals.

Michael R. Owen

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