What Material and Technique for Indicator Crystals?

markz528 · Dec 29, 2022

I'm trying to make new crystals for indicators. First one I am making is a 2 inch. Not having much luck.

I am using 0.030" PET plastic which I don't think is a good choice. I think it is too soft. I am milling it with a 60 degree end mill. I'm not optimized on speeds/feeds for PET and I need to clean off significant burrs, but that's not a deal breaker.

The issue is that that the plastic is getting damaged when I am inserting it into the bezel even if I leave the protection film on it. Its like its being damaged from the bending. I am using an aluminum insertion tool that my dad had made. I have a large set that he made and the tools are proven so I know its not the tool. I have just a little plastic material left from my dad, and it seems harder than the PET, but I don't know what it is. Somewhere my dad left me an instruction sheet with all the math on how the tools were made and maybe there is a note on there on material, but I can't put my hands on it right now.

I rather make my own than try to find premade ones, but maybe that is an option. I don't know if the sizes/fit are standard or not or where to go to buy generic ones.

And how do you cut your bezels?

Suggestions?

Joe Gwinn · Dec 29, 2022

I think that acrylic (plexiglass) is what is used. Look into jewelry supply houses for technical details of watch crystals. It may be that the same sizes are used by indicator manufacturers.

Milland · Dec 29, 2022

replacement indicator crystals - Google Search

jim rozen · Dec 29, 2022

1) go to the local craft store and find appropriate material. In my case this was thin plastic trays for casting decorative items. Bring a micrometer.

2) cut a rough square blank out of of this, about 2X the size you need.

3) put a piece if fine grained wood into a four jaw chuck and roughly turn a shallow depression in this, a bit larger than the diameter you're going to need for the replacement crystal.

4) sand the depression to get a good smooth finish on it.

5) remove the wood, and screw the square blank over the depression.

6) using a heat gun, heat the plastic to soften it a bit, and using a rag, press the material into the depression.

7) once it cools, chuck it back up and trepan the crystal out to the correct size.

8) start by trepanning larger then ypu'll end up with so you can use calipers to measure the OD.

9) once you get the desired size set, trepan on through. Be very careful as you break through the backside as they want to tear out at the last miniute.

10) best if you can get it thinned down to 3-5 thousandths so you can snap it out. Sand the edges smooth, polish with simichrome if neede, snap into place.

Make a few, the first one or two may not be the best. By the time you're on the third it will start to get good.

bosleyjr · Dec 29, 2022

Here's a video of a guy making an indicator crystal from craft 0.020" acrylic plastic off amazon. To make them, you need holders for the lathe, plus some rubber pressure pads. The guy doing this noted that the dead-center pressure plate heated up, so he made a live center with dual deep groove and one thrust bearing.

Then you probably need a Robur press to push the crystal into a concave (or convex - depends upon POV) shape. This decreases the od, and you drop your bezel onto the crystal and release pressure. Then you have a solid mount.
I've used pool (from a pool table) balls and pvc pipe in a vice to do the same thing for some starrett indicators I recrystalled. You can buy a watch crystal press for between $10 and $2700 (Rolex) on ebay. The nice thing about a purhased unit is that they have nice curved dies.

If you are making 10 or more, maybe this is worth it. If not, suggest you consider buying a crystal. Long Island Indicator has some crystals available for various indicators.

Spare Parts Lists

Spare parts for indicators, calipers and micrometers

www.longislandindicator.com

jim rozen · Dec 29, 2022

For a lot of dial indicators, you don't need a press. If the crystal is 5 or ten oversize, it will snap into place from the underside, and stay put.

bosleyjr · Dec 29, 2022

jim rozen said:
For a lot of dial indicators, you don't need a press. If the crystal is 5 or ten oversize, it will snap into place from the underside, and stay put.

Thanks, Jim. I used the pvc pipe and eight ball technique for some of my 3-1/2 inch indicators. It worked, but nice to know I won't have to do that again.

Bill D · Dec 29, 2022

I ddi not believe it until I tried. You can cut sheet glass with tin snips. Trick is the glass must be submerged in water which makes it hard to see and follow the line marked on the glass with a sharpie.
I believe the water damps vibrations so the glass does not shatter.

Screwmachine · Dec 30, 2022

G&S are the standard U.S. supplier of acrylic crystals for watches and indicators (in Europe it would be Sternkreuz). I've never ordered directly from them, but it seems you can, their site is pretty informative anyway.

Gauge Crystals — G-S Supplies, Inc.

www.gssupplies.com

More user friendly are some of the watch suppliers, like Esslinger. They carry G&S in flat, their "W Micron" https://www.esslinger.com/gs-watch-crystal-w-micron/, and domed (which I use on my Interapids) "PK" https://www.esslinger.com/gs-watch-crystal-pk-lo-dome/ .

For the 7-10 bucks they cost I can't see a compelling reason to make them.

rons · Dec 30, 2022

jim rozen said:
For a lot of dial indicators, you don't need a press. If the crystal is 5 or ten oversize, it will snap into place from the underside, and stay put.

I repaired a Starrett 120A and the crystal just snaps in. I took mine out to lightly buff it with light buffing compound. Then followed
with swirl remover. If needed in the future the crystal can be gently popped out and polished again.

boslab · Jan 1, 2023

Out of curiosity I wonder if the synthetic sapphire watch glasses could work?
Mark

Joe Gwinn · Jan 1, 2023

boslab said:
Out of curiosity I wonder if the synthetic sapphire watch glasses could work?

Yes, but there is a small problem:

https://www.newport.com/f/sapphire-parallel-windows

Gorilla Glass (used on iPhones and the like) might be a better option.

https://www.corning.com/gorillaglass/worldwide/en.html

markz528 · Sunday at 10:06 PM

Thanks for all the responses. I had seen that video but the material was too thin for my liking. The crystal I was replacing was 0.040" thick.

As mentioned, acrylic didn't work without premolding it. I ended up using polycarbonate around 0.030" thick. It came out good. I know that polycarbonate without coating is prone to scratching, so we will see how it does long term. I have several more to make.

This indicator lives again. Still need to calibrate it, but it seems to be working well.

DavidScott · Sunday at 11:08 PM

That did turn out nice but polycarbonate will typically be damaged/destroyed by chemicals or oils. Coolant or even skin oil can do it in, depending on the exact type.

EPAIII · Monday at 12:56 AM

Oh, for Pete's sake, just buy one. See posts #2 and #3.

jim rozen said:
1) go to the local craft store and find appropriate material. In my case this was thin plastic trays for casting decorative items. Bring a micrometer.

2) cut a rough square blank out of of this, about 2X the size you need.

3) put a piece if fine grained wood into a four jaw chuck and roughly turn a shallow depression in this, a bit larger than the diameter you're going to need for the replacement crystal.

4) sand the depression to get a good smooth finish on it.

5) remove the wood, and screw the square blank over the depression.

6) using a heat gun, heat the plastic to soften it a bit, and using a rag, press the material into the depression.

7) once it cools, chuck it back up and trepan the crystal out to the correct size.

8) start by trepanning larger then ypu'll end up with so you can use calipers to measure the OD.

9) once you get the desired size set, trepan on through. Be very careful as you break through the backside as they want to tear out at the last miniute.

10) best if you can get it thinned down to 3-5 thousandths so you can snap it out. Sand the edges smooth, polish with simichrome if neede, snap into place.

Make a few, the first one or two may not be the best. By the time you're on the third it will start to get good.

jim rozen · Monday at 10:14 AM

"Buy??" You mean like spend money? If I wanted to spend money I'd buy a new dial gage. What's the fun in that. Once I have the raw materials and setup, I can make whatever size I want. Small hobby: buying indicators that need TLC and setting them right.

dgfoster · Monday at 9:44 PM

markz528 said:
Thanks for all the responses. I had seen that video but the material was too thin for my liking. The crystal I was replacing was 0.040" thick.

As mentioned, acrylic didn't work without premolding it. I ended up using polycarbonate around 0.030" thick. It came out good. I know that polycarbonate without coating is prone to scratching, so we will see how it does long term. I have several more to make.

This indicator lives again. Still need to calibrate it, but it seems to be working well.

One other alternative that is simple but not nearly as elegant as removing the bezel and forming a crystal as was thoroughly lined out by Jim Rozen in earlier posts to this thread, is to simply 3-D print a snap-on bezel to hold an acrylic or polycarbonate replacement or add-on crystal. I did printed one first for an inexpensive pressure gage that gets banged around. That worked so well that I made a couple of add-ons for indicators that often have hot chips fall on them melting into the crystal. With the add-on crystal, I'll just pop off the plastic bezel, put on another acrylic crystal cover, and be back in business in no time. This is not a fix that most would want for the Interapids and such. But it is quick and dirty and actually add a little protective bumper (that could get in the way) to the gage.

Brief video of printed bezel

It took about 5 minutes to CAD draw the file for this bezel. It is parametric so that its diameter takes just a click to change. Printing took about 20 mins. Material cost is pennies.

These cheapo indicators see hard duty in my shop. A little extra bumper and a sacrificial crystal is a plus.

These bezels were printed in PLA which is pretty durable stuff. As is they are very stiff and would be difficult to collapse a strong grip I could also have printed them in PETG which is even more robust but PLA was already in the printer.

Denis

markz528 · Tuesday at 7:43 PM

jim rozen said:
"Buy??" You mean like spend money? If I wanted to spend money I'd buy a new dial gage. What's the fun in that. Once I have the raw materials and setup, I can make whatever size I want. Small hobby: buying indicators that need TLC and setting them right.

Exactly! Plus, I have no idea how I would buy a crystal that would actually fit. The ones made for specific models are one thing, but for these old antiques?

jim rozen · Tuesday at 7:50 PM

I really HATE going to CAMA because there's a plethora of inexpensive, semi-busted indicators.

EPAIII · Tuesday at 8:31 PM

Well, excuuuu uuuu uuuu use me. Silly thought.

jim rozen said:
"Buy??" You mean like spend money? If I wanted to spend money I'd buy a new dial gage. What's the fun in that. Once I have the raw materials and setup, I can make whatever size I want. Small hobby: buying indicators that need TLC and setting them right.

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