[time-nuts] Vibration isolation of quartz oscillators

[Wes]

In my youth I worked for a time in my dad's automotive machine shop.  We did a 
lot of work on medium-sized industrial engines, Cummins V-12s, GMC V16-71s, 
International TD-24s, etc. To handle these we bought a Van Norman crankshaft 
grinder, a sizable machine, which I operated.  The shop was in downtown Tucson, 
right across the street from the (then) Southern Pacific Railroad tracks.

The grinder was originally installed right on the 6" thick concrete slab floor.  
It wasn't long before I noticed that if I was grinding a journal when a trail 
rumbled by I got runout and had to pause grinding until the train passed  We 
wound up moving the machine and digging a hole about 2-3 meters deep and about 2 
by 3 meters "square", lining it with fiberboard and filling it up with concrete 
and reinstalling the machine on top.

About two years ago that building was demolished as part of a "modernization" of 
downtown (it's still a vacant lot) and I wondered how surprised they were when 
they went to remove the slab.

Wes  N7WS


On 6/28/2020 8:05 AM, Dr. David Kirkby wrote:
> Dr David Kirkby Ph.D C.Eng MIET
> Email: drkirkby at kirkbymicrowave.co.uk Web:
> https://www.kirkbymicrowave.co.uk/
> Kirkby Microwave Ltd (Tel 01621-680100 / +44 1621-680100)
> Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3 6DT.
>
>
>
>
>
> On Sun, 28 Jun 2020 at 12:44, Tom Van Baak <tvb at leapsecond.com> wrote:
>
>> About slabs and stability... Around the world there must be a hundred
>> precision time labs, including official NMI (National Metrology
>> Institute) labs that contribute to the calculation of UTC itself. You
>> run into photos of these labs and their T&F gear on the web all the time
>> when you search for time nutty stuff. Those of us with home labs -- even
>> if just a few vintage frequency standards -- can relate.
>>
>> Anyone, one of my favorite lab photos is from VSL, the Dutch Metrology
>> Institute. Photo attached. [1]
>>
>> Spend time time pan/zooming around the gear in the photo. The usual
>> suspects: hp 105 quartz; TimeTech (I think); lots of SDI
>> (Spectradynamics); also Truetime or Symmetricom stuff; maybe that's an
>> old Tracor/Fluke VLF receiver on the far right (?); and of course lots
>> of Stanford Research SR620 counters, the TIC still used by almost every
>> time lab.
>>
>> But what really caught my eye was not just the four hp 5071A in the
>> foreground but *how they are mounted* -- on top of massive granite blocks!
>>
> There's a picture of a granite block here, at a former place I used to work
> as a student - EQD Aquila, the MODs calibration labs.
>
> https://www.derelictplaces.co.uk/main/military-sites/14101-aquila-mod-testing-facility-bromley-march-2004-a.html#.XvirQuco9PY
>
> about 60% of the way down the page. (Some of the pictures are quite
> amusing, as well as some of scientific interest).
>
> There's a couple of guys at my radio club used to work somewhere where a
> milling machine was turning high precision device. I just phoned one to ask
> what they used for anti-vibration, as I knew they took some precautions. He
> said they had dug a hole about 2 m into the ground, above that was 600 mm
> of "rubber", then 1.4 m of reinforced concrete. That used to stop lorries
> messing up the work. That's a different sort of application.
>
> I assume the OPs objects are quite large - not wrist watches. Otherwise, I
> was wondering if an active damping system might be practical. They
> certainly exist for laser tables
>
> https://www.newport.com/n/active-vibration-damping
>
> but I would imagine that for heavy 19" rack equipment, there would need to
> be quite a bit of power consumed in such a system. I've never done any
> calculations - just intuitively, I can't imagine that one could achieve
> anything useful without some pretty big power amplifiers.
>
> When I worked at UCL we had a laser table. Our department was near a main
> road. The laser table had gas-filled "dampers", but apparently these made
> the vibration problems worse rather than better, so the gas was removed. We
> never had any active system.
>
> Dave
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