Hi

> On Feb 4, 2018, at 7:13 AM, Poul-Henning Kamp <p...@phk.freebsd.dk> wrote:
> 
> --------
> In message <480971424.644410.1517715556...@webmail.xtra.co.nz>, Bruce 
> Griffiths
> writes:
> 
>> It has been used to machine/polish crystal quartz waveplates and
>> to machine/polish the surface of silicon wafers before uses for
>> MEMS fabrication. Its even been used to carve channels in silicon
>> wafers in such applications.
> 
> The images on this page gives a good impression about the current
> skill-level in that area:
> 
>       https://www.azonano.com/article.aspx?ArticleID=2740 
> <https://www.azonano.com/article.aspx?ArticleID=2740>

The gotcha is shown in the pictures. First point is that they are etching *very*
small features. A 5 MHz 3rd overtone blank is way thicker than what they are 
playing with. The second issue is that even at small scale the walls are going 
non-parallel. I seem to remember that you need straight walls on the cuts to
keep everything happy in terms of reflecting sound. 

There *is* a lot of work done on odd shaped crystals. Your wrist watch has a
good example of that in it. It all comes down to what sort of process is 
required 
to achieve the result. With the BVA the real answer is that you can do a mount
that achieves the same thing for a lot less money. 

Either way, you are simply taking care of one plane (just like the SC). Forces 
in the real world rarely are nice enough to only show up in one plane ….

Bob


> 
> I'm pretty sure that it is not the machine control but rather the
> metrology that would be the challenge.
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> p...@freebsd.org         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.

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