Re:Microswitch repeatability

just a slightly off topic aside, but is it possible to use a micro switches
pulse for 'counting' for crude measurement purposes,i.e. setting one up to
run (bounce) along the crests of a threaded rod say 10 TPI which would in
itself be set up alongside the edge of a moving machining table. (micro
attached to table) Perhaps table driven by ball screw (cut not rolled) and
simple electric drive OR by pneumatic cylinder??
Just a thought
Raynor J
-----Original Message-----
From: CAD_CAM_EDM_DRO@onelist.com <CAD_CAM_EDM_DRO@onelist.com>
To: CAD_CAM_EDM_DRO@onelist.com <CAD_CAM_EDM_DRO@onelist.com>
Date: Saturday, July 17, 1999 12:54 AM
Subject: [CAD_CAM_EDM_DRO] Digest Number 94

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>There are 2 messages in this issue.
>
>Topics in today's digest:
>
> 1. vibration sensivity
> From: "Elliot Burke" <elliot@...>
> 2. microswitch repeatability
> From: Ted Robbins <rtr@...>
>
>
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>Message: 1
> Date: Thu, 15 Jul 1999 23:55:05 -0700
> From: "Elliot Burke" <elliot@...>
>Subject: vibration sensivity
>
>This isn't really too onerous a constraint. Of course, if you are trying

to

>measure vibration, interferometry is a good way to go. A classic

experiment

>measured eardrum displacement invivo on the order of 0.1 nm.
>In my experience, most moderately rigid setups and tools are adequately
>rigid for interferometry. If there is movement or vibration that you can
>feel, then most likely the interferometer will detect it too.
>I have frequently made interferometers on 2x4's will excellent results.
>Antivibration mounts under honeycomb tables are often sold for
>inteferometric applications. These are rarely needed, and serve mostly to
>intimidate the uninitiated. Mostly I disconnect the air suspension, since
>it makes the table rock when weight is shifted. Things don't get noticably
>more stable with the air on.
>
>Elliot Burke
>
>>Message: 11
>> Date: Thu, 15 Jul 1999 20:17:23 -0700
>> From: Bill Martin <wwm@...>
>>Subject: Re: counts per inch, my $0.02
>
>>What about them being "too" sensitive, as in picking up all the
>>vibrations from the machine, the building, everything moving nearby?
>
>>Bill Martin
>
>
>>Elliot Burke wrote:
>>
>> From: "Elliot Burke" <elliot@...>
>>
>> If the DRO is used with a Twyman-Green interferometer using a HeNe laser
>at
>> 632.8 nm wavelength, a fringe count will occur every 312.4 nm, which

comes

>> out to 80278 counts/inch.
>> Other types of interferometers may have twice this sensitivity.
>> Shorter wavelengths (doubled YAG at 532 nm) will have even more
>sensitvity.
>>
>> For those interested in using interferometers to measure distance, a
>> suitable laser source costs much less than $100. The optics required
>aren't
>> too complex. Basic precision can be 0.5 ppm, if the temperature and
>> humidity of the air path are compensated for.
>>
>> Elliot Burke
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>Message: 2
> Date: Fri, 16 Jul 1999 01:03:04 -0700
> From: Ted Robbins <rtr@...>
>Subject: microswitch repeatability
>
>Jon
>A number of years ago I was amazed to see a boring mill with an automatic
>homing cycle on the measuring rods lying in a rod trough. It used a
>standard leaf actuated micro-switch. I checked it with a micro-cator and
>found it repeated within a few "tenths". I checked a few other
>micro-switches chosen at random and was surprised again to find that they
>all repeated under a thousandth, most within 2 to 3 "tenths". (A tenth in a
>machine shop refers to a ten thousandth of an inch. I think the probe
>would work as long as that repeatability is close enough and the probe is
>lowered reasonably slowly enough.
>
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