Re: [CAD_CAM_EDM_DRO] Re: Digital Caliper Output

How accurate is commercial rack? It might be possible
to simply use a Stock Drive Products rack and a zero backlash gear.

For that matter, I bet somewhere somebody makes a nice long
dial caliper.

You don't need to grind the ends. Mount the racks so they
overlap a few teeth on the end. Take a piece of straight, small diameter
stock and lay it across the teeth. carefully shift one of the racks until
the stock is at right angles to the rack. The tooth profiles holding
the stock are now lined up. (another way to do this is to put a third
rack upside down atop them. The three won't mesh until the racks are
aligned properly.)

Or (and this is REALLY sick), close wind some steel wire around a rod and
clamp at the ends. Polish. Mount an angled mirror (hey, it's an autocollimator!)
on the moving part, and fire laser through the system. As it passes over each
bump the return beam in the autocollimator will swing through an arc. Glue a
tiny chip of microscope slide cover to a speaker, drive the speaker, and
when the angle of the speaker position cancels the angle of the reflection
off the wire, the beam will end up in the detector. You may want a direct
detector for counting the motion during fast traverse.

Other sick ways to measure linear position -

Mount a good heavy piece of V thread all thread (say 2", you don't want it
to bend) between centers &
spin it. Mount a needle on the moving part almost touching the outer
diameter of the thread. Feed RF into the needle.
Each time the screw comes around it'll capacitively couple and produce a
spike. Put a chopper wheel on the end with an extra channel for a zero
reference.

Yes, you'll only get a fuzzy "blip", but it's a fuzzy blip in a vernier measurement.

Uh, has anybody confirmed that a hard steel roller on a hardened surface (say
a ball bearing race on a track) will actually slip if you roll it back and forth?
If it doesn't, etch a pattern on it and read with optics.

Or, if you'd just as soon fiddle with some nasty electronics, how about a plunger in
a rectangular tube? Feed in microwaves and adjust frequency until it resonates.

excite a length of metal (music wire?) rod with an ultrasonic vibration. Clamp end firmly
to get a nice clean bounce. put a phonograph
needle against the rod with a cartridge. Sweep frequency up until you get a resonance
null. Probably need some coarse measurement backup to back it up.

Any of these, the follower can probably be put on the end of a beam and the
whole enclosed in a box. The beam exits through the top. All nice and enclosed,
no swarf on me.

Annie "don't ask me how to measure the temp. of liquid helium" ogborn