DIY measuring and lapping a worn surface plate

[Paul Alciatore]

I am not putting down what he did. It is an excellent job and I am sure, and I mean that seriously, I am really sure that when he was finished that he had a very good plate. It was much, much better than when he started. And it will be a big asset to his shop.

But I do have a small word of caution here. The pros do not rely on just the repeat-o-meter. The repeat-o-meter does not measure flatness. It can only tell you if the surface deviates from a perfect sphere. That sphere can be concave, flat, or convex and, using only the repeat-o-meter, you can not tell the difference. If you want to verify flatness with a repeat-o-meter, you must first calibrate (zero) it on a known, flat surface. A surface plate that is known to be flat, even a small one, can be used for that calibration and then the repeat-o-meter can be used to check other plates, even larger ones. Of course, as the second video shows, other instruments can be used to check the plate for flatness or to find an area on a plate that is flat where you can then calibrate the repeat-o-meter.

I definitely learned something here.