[ARC5] WHINK and crystals.

Bruce Long coolbrucelong at yahoo.com
Sat Jun 29 16:19:44 EDT 2013 

I doubt very much optical flatness is required for grinding a crystal.  It is difficult to decide what degree of flatness is adequate from comparison with modern crystal manufacturing practice as most modern crystals have a lens shaped cross section to reduce spurious responses.  Having said that the contour grinding buckets are nothing more than sell or maybe even cast iron.

The planetary blank grinding machines use ordinary steel surfaces ground flat with ordinary machine shop grinders.

For this reason  I suspect  ordinary flat float (plate) grass is good enough for occasional use.  The next step up would be to buy a small flat of precision ground steel plate from mcmaster carr or the like.

I suspect the grinding technique- ie uneven pressure,  not using figure 8  or equivalent grinding motion is the larger problem



________________________________
 From: J. Forster <jfor at quikus.com>
To: Dennis Monticelli <dennis.monticelli at gmail.com> 
Cc: ARC-5 Maillist <arc5 at mailman.qth.net> 
Sent: Friday, June 28, 2013 12:32 PM
Subject: Re: [ARC5] WHINK and crystals.
 

Optical flats come in all sizes. I have a 16" one, about 3" thick, that I
got surplus years ago.

I really think a piece of plate glass, like a very small table top, will
work just fine.

I'd go to a local glass shop and ask for a piece of scrap, then pay a few
bucks to get the edges sanded unsharp.

YMMV,

-John

==================


> True, though they are much smaller than your typical 8" reticule.
>
>
> On Fri, Jun 28, 2013 at 9:19 AM, J. Forster <jfor at quikus.com> wrote:
>
>> Optical flats, used w/ LASERs are probably a whole lot flatter. They are
>> often good to 1/100th of a wavelength of roughly 500 nM light, or 5 nM.
>>
>> They are pretty expensive though. Think $300 for a 1" OD, 1" thick one.
>>
>> You can sometimes be picked up cheap on eBay.
>>
>> -John
>>
>> =================
>>
>>
>>
>>
>> > Good input, Hutch.
>> >
>> > There is NOTHING flatter than a glass reticule.  We're talking
>> microns.
>> >  These are very hard to find, even here in Si valley among all the
>> surplus
>> > shops.  The reason is not just recycling, it has more to do with the
>> fact
>> > that these masks represent the IC design itself and all such
>> information
>> > is
>> > deemed highly proprietary.  Hence this stuff just does not end up in
>> the
>> > surplus channels.
>> >
>> > Dennis AE6C
>> >
>> >
>> >
>> >
>> > On Fri, Jun 28, 2013 at 8:21 AM, John Hutchins
>> > <jphutch60bj at gmail.com>wrote:
>> >
>> >> Group -
>> >>
>> >> This is good information,  is the procedures and materials and
>> process
>> >> document existing on a web page?
>> >> Can the whole process be summarized?  If so since radio sites go up
>> and
>> >> down, same as with "yahoo group participation" could this be a
>> Wikipedia
>> >> page?
>> >> On the subject of Glass:
>> >> Glass plate you say,  find if you can;  glass used in making IC chips
>> >> called a reticule;  This is very hard and thick glass, flatter than
>> the
>> >> world before Columbus!
>> >> They used be very common and were discarded all the time;  Now
>> reticule
>> >> glass is recycled, but you may still have some sources out there.
>> >> Hutch
>> >>
>> >>
>> >> On 6/28/2013 8:55 AM, J. Forster wrote:
>> >>
>> >>> The guy used a mirror, probably because it was a cheap 'optical
>> flat'.
>> >>> Ande distortions are readily noticeable. Today, with 'float glass'
>> >>> probably any glass plate from a hardware store will work...  thye
>> >>> thicker
>> >>> the better.
>> >>>
>> >>> As to grinding medium, fine gvrinding powder for amateur telescope
>> >>> makers
>> >>> is worth a try. It comes is a wide variety of grits, from gravel to
>> >>> rouge.
>> >>>
>> >>> -John
>> >>>
>> >>> ================
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>  Gentlemen,
>> >>>>
>> >>>> For whatever it may be worth, I had occasion to observe a fellow
>> radio
>> >>>> amateur and CAP communications person who regularly ground
>> crystals.
>> >>>> I
>> >>>> recall that he would accumulate a large number of FT-243 crystals
>> of
>> >>>> varying frequency and put them on the CAP frequency of 4585 kHz.
>> He
>> >>>> did
>> >>>> a combination of lapping and etching.  I recall that he used a
>> >>>> heavy-duty mirror surface for lapping.  The one thing I also recall
>> >>>> was
>> >>>> that, for periodic testing, he used two electrodes (sic) from an
>> >>>> FT-243
>> >>>> holder with leads attached and held the thing together with a stout
>> >>>> wooden close-pin. This was wired into an oscillator which, in turn
>> was
>> >>>> hetrodyned with a BC-221 into a receiver (Remember, this was in
>> >>>> probably
>> >>>> 1959).  Apparently, the pressure was what was need to emulate the
>> >>>> pressure the holder would provide.  He made crystals for CAP for
>> >>>> probably 20-plus years with very good success.  I recall the
>> >>>> "figure-8"
>> >>>> pattern he'd use to lap/grind the crystals.  I do not know the
>> >>>> chemicals
>> >>>> nor compounds he used, but suspect it what you all mention, here.
>> I
>> >>>> may
>> >>>> give it a try as I have some crystals near 3885 that are within
>> >>>> reasonable distance down the band.  We'll see!
>> >>>>
>> >>>> Jeep K3HVG
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