Replacing crystal in Starrett indicator - is there a catch?

I bought a pair of used dial indicators last week and they would be much improved with new crystals. I haven't opened one up yet, but it looks like I'll have to go in through the back. Am I wrong?

If so, is there any real difficulty in doing so? I'm pretty good with putting things back together after they've been disassembled, but I've not worked on an indicator yet.

These are 25-511's, so I think they're worth the trouble of doing it myself.

Thanks,
Pete

Before you try to take them apart, use a little Brasso on a clean soft rag to polish them. It works surpisingly well...

IF you have to take off the crystal, usually there is a tiny slot in the bezel ring; turn the bezel until you see a little shiny spot in the slot and then use a fine blade or screwdriver to push in on the shiny spot. Then rotate and pull on the bezel, it should come off.

The shiny spot is one of the corners of an almost-round spring (more like a triangle) The corners engage a groove in the bezel, the sides of the triangle engage a groove in the housing.

Go to http://www.longislandindicator.com/. They can talk you through crystal replacements, and sell you the parts as well.

Andrew

Long Island indicator has a crystal press for installing the new crystal or you can rig something up to "cup" the new crystal slightly upward.

I've removed crystals with a piece of duct or shipping tape firmly planted in the middle of the crystal and pulled up quickly ... a dangerous method indeed

Sometimes a crystal can be renewed by buffing with fine compound to remove scratches. This generally won't remove discoloration but can make it water clear again.

Den

Isn't this really a job for a specialist like the aforementioned Long Island? After repair an instrument really should go to metrology next to be recalibrated. Any kind of instrument, not just machinists.

I used a hand valve grinding tool with suction cups to get mine out and back in.

Oooops - just let one of those magic tricks out of the bag.

Chrisp

lunkenheimer - You mentioned a spring to hold the crystal in the starrett indicator? I took one apart and saw nothing other than the crystal? Is the spring flat or round? I assume it is designed to keep the crystal from putting pressure on the hand? I tried to put a thin glass one in instead of the original plastic. Thought it might hold up better but I need to see what the spring should look like.

Markus

Bcstractor, Thanks ! Hadn't thought of that

Markus, On several indicators I've worked on, a spring similar to the one mentioned held the bezel on, not the crystal.

Den

lunkenheimer wrote: "IF you have to take off the crystal, usually there is a tiny slot in the bezel ring; turn the bezel until you see a little shiny spot in the slot and then use a fine blade or screwdriver to push in on the shiny spot. Then rotate and pull on the bezel, it should come off."

Thanks, I got the bezel off using this instruction. Now I'll order the new crystals. The existing crystals are yellowed, so I don't expect polishing will help, but now that I can safely remove the bezel I'll take a try at it.

Dennh wrote: "Long Island indicator has a crystal press for installing the new crystal or you can rig something up to "cup" the new crystal slightly upward."

Great idea. A fellow wrote something similar on r.c.m yesterday in a thread someone else started.

Canonicalman wrote: "Isn't this really a job for a specialist like the aforementioned Long Island? After repair an instrument really should go to metrology next to be recalibrated. Any kind of instrument, not just machinists."

It is my hope that by taking the bezel off, I won't disturb the indicator mechanism and a recal won't be needed. At some point I will get the recal done, but I'm just trying to get these in working order.

Thanks for all your help!!
Pete

A lever indicator isn't really "calibrateable", because the deflection vs dial reading has a built in error due to the pivoting arm.

A plunger indicator is calibrateable, but the ratios are locked-in by the grears.

If you have a set of traceable gage blocks, you should be able to "calibrate" every normal small absolute or relative "distance measurer" in the shop to satisfy ISO, etc. In most cases, the measurements are coarse enough that temperature isn't an issue, since it wouldn't move the reading a visible amount.

Even if you have "uncalibrated" gage blocks, if they are from a reputable source (B& S, etc) they likely are not far enough off to make a difference unless you need traceability. For chinese, indian or whatever ones, they might be great, or they might not beworth anything.

Pete,

I have a book written and published by Michael T. Yamamoto (no kidding) titled "Repair of Mechanical Dial Indicators and Calipers" The ISBN number is 0-9679279-4-3. The book is quite extensive and covers a number of different brands, including Starrett. I believe I saw an add for it in either HSM or Projects in Metal. Cannot remember which one.

Fred