Mitutoyo Caliper Crystal?

Well ... I've not dealt with a Mitutoyo dial caliper, but I've made crystals for various sizes of dial indicators.

1) Find or buy a clear plastic of the appropriate thickness. For the larger calipers, I use 1/16" Lexan. For dial calipers, I might go for one of the fairly large clear bottles flexible with gentle curves -- as an example -- the ACT floride mouthwash bottles are probably about right in thickness. 2) Measure the inside diameter of the part of the bezel which holds the crystal. (First -- make sure that you have a way of removing the bezel before trying that -- just to be sure.) 3) Make a set of pushers (one held in a 3-jaw chuck in the lathe, and one with a center to match a tailstock live center) which are just slightly below that measured diameter.

I like to relieve the centers so they only touch for about 1/4" radius at the OD.

4) Trap the plastic (with protective paper to prevent scratching) between the two pushers above, and with a very sharp tool, turn the OD down until it is a little larger than the measured ID of the bezel ring.

How much larger is a function of how much dome you need. If the center hub of the needle is high, you will need more dome than otherwise.

Make two or three of these with slightly different diameters for a first try.

If the plastic is thicker than the step of the bezel ring, bevel it while it is still between the pushers for better appearance.

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5) Turn a cylinder whose OD is a bit smaller than the ID of the bezel ring -- perhaps 1/4" smaller diameter for a dial caliper, somewhat more for a 3" diameter dial indicator.

Bevel the ring on both ID and OD, and then (using a file or whatever works for you) round the edge as much as possible, and polish it as smooth as possible. I have used steel, aluminum, and Nylon -- depending on what I had which was close to the needed size.

6) Turn a pusher -- OD small enough to easily fit through the bezel ring, with a step and then a diameter easy to grip in the chuck on your drill press.

I have used steel and Nylon to make these. The only reason that I have not used aluminum for this is that I did not have any of appropriate size when I was making them.

Crown it smoothly -- with a radius somewhat smaller than the crystal will eventually have. Polish it as well.

7) Using a soft flexible plastic (the Lexan comes pre-coated with such plastic) protect both the bottom and top surfaces of the crystal which you have made above.

Trim the inside plastic (which will be facing up) so it is smaller than the smallest ID of the bezel ring.

8) Place the crystal on the smooth ring on the cylinder on the drill press table. If you had to bevel the edge, the beveled side goes facing down.

9) Grip the pusher in (6) above in the drill chuck. Offset the drill press table as necessary to have a smooth surface under the cylinder.

10) Holding the bezel ring in your left hand, move it up around the pusher, and bring the pusher down into contact with the center of the crystal.

11) Gently apply force using the drill press' quill feed.

The crystal will take on a dished shape, and the OD will reduce as you do this.

When you have it small enough, you can slip the step of the bezel ring over the OD of the crystal, and when you relax the pressure on the quill, the OD will expand to firmly grip the ID of the bezel ring.

12) Peel off the protective plastic on the inside of the crystal.

You may also wish to peel off the protective plastic on the outside as well -- or you may wish to wait until the calipers are fully assembled.

13) Make sure that the dial is properly oriented (sometimes there is a key to prevent it from rotating relative to the bezel ring) and assemble the bezel ring to the calipers.

Now -- if you have not yet done so -- peel off the protective plastic and admire your handiwork.

If you're going to be doing a lot of these, take a 1/2 ton arbor press, and drill the end of the rack to accept the pusher shank. I've been planning to do this, but have not yet done it. :-) While you're about it -- make a platform for the cylindrical support ring -- perhaps with features to hold things properly centered without having to slide things around.

Enjoy, DoN.

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A very nice wite up DoN. Thank you!

Errol Groff

If you've got a lathe, you can make it out of Plexiglas in less than a half hour. First, put a chunk of metal bar in the lathe and face off cleanly. Superglue the Plexiglas to the bar. Cut the OD to match the bezel, relieve the inside to clear the pointer and pointer shaft. Polish the inside with jeweler's rouge. Bevel the back side some, this will be the outer face of the crystal. If the center is real thin, you may want to use heat and/or acetone to remove from the mandrel. If you left it fairly thick, just yank it off. Scrape the remaining superglue off with an Xacto knife and then polish the top.

Jon

Well, I guess my method is more primitive, but I used to keep around a few old, defunct dial indicators of various mfr's.

When I needed a new lens, I just made a little one out of a bigger one, and put it in.

Flash