[time-nuts] Super stable BVA Quartz resonators... BVA??

Chuck Harris cfharris at erols.com
Mon Dec 10 13:19:20 UTC 2007


Bruce Griffiths wrote:
> Bernd T-Online wrote:

>> Bi-convex contours are more difficult to manufacture, as it is required 
>> that the symmetry axis of the upper and lower contour must coincide. 
>> Also other parameters become worse. For the BVA the manufacturability 
>> would also be much worse as it already is.
>>
>> Regards
>>
>> Bernd
>> DK1AG
>>   
> Bernd
> 
> Whilst traditional optical edging techniques can easily remove any wedge
> when both surfaces are convex, maintaining alignment of the "lens" axis
> with respect to the crystal axes is another matter, at least when using
> traditional surfacing techniques, with computer controlled surfacing
> techniques even this can be done.
> 
> With a planoconvex "lens" bias polishing or an equivalent technique can
> be used to adjust the inclination of the plano surface with respect to
> the crystal axes and this alignment is maintained during edging leaving
> only axial thickness adjustments to be made. The etching process used to
> remove cracks and defects after mechanical polishing is anisotropic
> which may introduce further complications in maintaining alignment and
> shape.
> 
> Bruce

So Bruce, what source did you read that led you to change your original
answer from --it's easy--, to --it's difficult--?  (reference your quoted
text below:


 > Bi-convex contours are more difficult to manufacture, as it is required
 > > that the symmetry axis of the upper and lower contour must coincide.
 > >
That problem was solved over a century ago in optical lens manufacture.
If the two surfaces are spherical, then such decentering is equivalent
to adding a wedge, which is easily removed by optical centering and
edging techniques.
 > > Also other parameters become worse. For the BVA the manufacturability
 > > would also be much worse as it already is.


-Chuck Harris




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