[ARC5] WHINK and crystals.

J. Forster jfor at quikus.com
Sat Jun 29 18:28:35 EDT 2013 

> I doubt very much optical flatness is required for grinding a crystal. 

I never said it was. I merely commented on the properties of optical
flats. In fact, I suggested getting a piece of scrap glass plate from a
glass store.

-John

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

> 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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