How to Measure Dimension Without Disassembling the Lathe?

I may be able to help, did a lot auto part gaging (in-process and offline) in the 90s so exactly which dimensions/characteristics are you trying to measure?

you might try fine iron powder and a magnet to show you the parting lines. Maybe even a ferro fluid (fine iron powder in oil) a field along the length will show field concentrations at the air gap as the ring is a far better field path than the air gap, so there will be a fringe at the gap.

if they are solid to the mandrel will they not be all the same? Unless the nadrell iss off center slightly, but with rings, they flex, so these rings are then cut, I assume.

Another idea along the same lines as the fine iron power is liquid dye penetrant. It is simple to use and is used to locate cracks or in your case parting lines on parts. It comes in several types and sensitivities. My suggestion would be to use the visible type rather than the fluorescent type which has certain lighting requirements. The visible type can be obtained in a spray can and simply sprayed on. There is a dwell time of about 10 minutes and the penetrant is simply cleaned off. The penetrant is drawn into the voids of the parting lines. A white powder developer can be used to make the indications more visible but not required. The indications show up as thin red lines. A google search came up with a lot of information on the process. A company that deals with non destructive testing supplies should beable to answer any questions that you may have and would beable to supply you with the proper products for your requirements.

For what it's worth, I hope I have answered at least part of your question.

If you are profiling each ring in a stack the position of the part line is critical & although the dye penetrant method will show this up, you still have to measure it accurately. I wonder if either laser or optical measurement will do the job. With the optical method it would be possible to zoom in so that it might be possible to pick out the part line.

Place a ring of thin hard brass or bronze between every two rings!

Thats the best and cheapest idea yet. PT Dye (liquid Penetrant) is not cheap especially for a process of machining piston rings. Use this guy's idea!

i want to see the jo b at site than i solve the problem

paint the rings with red coat than put on mandl

The answer to the question of dimensional variation is yes, depending on the tolerance set on width you will have a build up of error....ie 0.125" +- 0.001" and you have set up the program for 0.125" x 50 components your last ring will have a error of 0.050" if they are all on the plus side....set up program for incremental rather than absolute in Z axis or surface grind rings to a finer tolerance.This will also take the guess work and need to measure on the mandrel out as they will always be the same width after grinding and size after machining.

The key is always reduce the error to achieve a better result.

nice one

seems to me that all these other ideas are more usfull when working out of a shed

this is the only true fix......yeah you could paint every ring but why?