Dial Indicator crystal: How to replace?

What is the easiest way to replace the broken plastic crystal on a dial indicator? I'm sure I could attach an oversize crystal to a temporary arbor and
trim it to size on the lathe. But I would bet someone knows a better way. Even if someone can tell me where to get oversize replacements, that would be a start... Thanks.
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On Tue, 29 Sep 2009 20:18:35 -0700 (PDT), Planet10

See: http://www.metalworking.com/dropbox/_1999_retired_files/DGAGE.TXT Gerry :-)} London, Canada
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Gerald Miller wrote:

There's also a post in the RCM archives (Google groups) on how the make a crystal using air pressure to form a heat-softened blank. I've tried it twice: I shattered it once with too much pressure and not enough heat, and blew a hole the 2nd time with too much heat. I'm hoping the 3rd time will be better.
Bob
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I did this a few years ago. I had a dial indicator with a damaged crystal. The "manufacturer" had never heard of that particular model when I called. I'm guessing that it was 40 to 50 years old.
I cut a disk from some thin, 1/16th(?) inch Lexan. To put a crown in it, I found a coffee mug of the right size and with an appropriately dished bottom. I put the coffee mug in the oven upside down and slowly heated it until the new crystal sagged and matched the curvature of the coffee mug.
IIRC, I scribed a circle of the right size, i.e., slightly larger, ~1/8th inch larger in diameter than the final size. I carefully cut the Lexan with an Xacto knife or single-edged razor blade
Bob S

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Planet10 wrote:

Here's a start: http://www.toolsgs.com/cart/browse.asp?subcat%2 http://www.toolsgs.com/cart/browse.asp?subcat%1
And particularly: http://www.toolsgs.com/cart/detail.asp?product_id=HP-5
The rest is a total mystery to me. Good luck!
--Winston
--

I'm still waiting for another sublime, transcendent flash of adequacy.

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I thought these might be standardized sizes under the AGD specs but a quick check shows there is still a min max range for each AGD group.
Reputable brands should have exact replacement parts available in exchange for $$.
Next simplest is probably to find an import dial that you can harvest the lens from and trim as necessary. Any dial worth fixing is worth sacrificing a $10 HF import for IMHO.
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Planet10 wrote:

Watchmakers have selections of these in graduated sizes, and a thing with a suction cup and fingers to deform the outer edge to slip into the groove in the "watch". But, you can make a crystal out of sheet Plexiglas, and relieve the inside face in a step, and bevel the outside edge. then, just glue it into the bezel. That's what I did for a Federal indicator that was missing the crystal. I actually like the flat crystal better than the curved ones, there's no reflection of lights. I super-glued the front of the crystal to a freshly faced piece of steel, did all the relieving of the inner face and OD, then just snapped it off the arbor, and peeled the glue off with a pocket knife. I polished the inner face while on the arbor, the front after it was off.
Jon
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Is this link any help to you?
http://longislandindicator.com/index.html
--
Michael Koblic
Campbell River, BC
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    Actually -- capture it between a round piece held in the lathe chuck and another held in place with a live center. Relieve most of the diameter of both, so they press only near the needed OD.
    Turn the material (1/16" Lexan if you are talking about a 2-1/4" diameter dial indicator or so, thinner if a runout indicator) to just a few thousandths of an inch larger than the ID of the hole in the bezel ring. Bevel about 1/2 of the thickness for appearance. (Angle is not critical.)
    Turn a ring about 75% the diameter of the fitted crystal. Make a smooth turn on the end and polish it smooth. Turn up another piece (perhaps 50% the fitted diameter) and crown it on the lathe and smooth and polish it as well. Turn a 1/2" diameter pin on the back of this.
    Place the ring on the table of your drill press, or on an arbor press. Fit the crowned piece in the drill press's chuck, or to the bottom of the arbor press's ram.
    Place the crystal, bevel side down, on the ring (it is good if you leave the protective film in place on both sides until you have it mounted in the bezel ring, to minimize scuffing of the crystal). Place the bezel ring on the top side of the crystal, lower the crowned piece in the drill press chuck until it presses the center of the crystal, and apply force while trying to fit the bezel ring on the crystal. As you press the center down, the outer rim will move up, and the OD will decrease slightly. When it is small enough, the bezel ring will drop in place, and when you relax the pressure from the drill press, the OD of the crystal will expand and grip in the bezel ring. Now peel off the protective film. (Proably you should partially peel the film on the back side and trim the film just enough so it does not get trapped in the bezel ring.
    Anyway, this produces a very nice looking domed crystal for most indicators.

    Well ... the above is how I make crystals for dial indicators and small runout indicators. The main trick is figuring out how the bezel ring removes from the indicator. There are quite a few ways, and if you mention the brand I (or someone else here) can probably give you a hint or two.)
    Good Luck,         DoN.
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