Recently, I found a nice offer on Ebay, an Etalon 77.19000 height gauge, along with a ultra high resolution Mahr LVDT length sensor. About the sensor, we will hear later, but the height gauge, although sold as “working”, didn’t work.
Still in good mechanical shape, and all Swiss Made. Mitutoyo has a very similar model, 192-130, which sells for well over 600 EUR.
The mechanism uses a rack and pinion design, with two pinions, one tensioned by a spiral spring, to avoid backlash. Practically, even without the spring – which was bent – there is no noticeable backlash.
There is also a second rack, and this drivers a fully independent counter mechanism.
After some examination it became clear that one of the pinions had a broken shaft, and this also let to the other pinion spring being damaged. The spring was easily fixed, but the broken shaft of such a tiny and hardened pinion, hard to fixed. I managed to drill a hole with a carbide drill, but when pressing in a new shaft, the whole thing broke apart…. a disaster.
Looking around in my drawers, I would this cheap Chinese dial, 0.01 reading. What if it uses the same rack pitch? Indeed, it does. The dimensions seems to correspond to a module 0.2 gear, and examination under the microscope showed identical tooth count on the pinion. Only the drive gear is a bit different but this could be pushed off.
The gutted dial, well, it is less than 10 USD.
To assembly it, I cut off and ground the lower part of the old pinion to a diameter a little bit less than needed, made a sleeve from stainless steel, and ground a suitable cylindrical length of the spare pinion so that all can be pushed together and fixed in the sleeve to form a new gear assembly of the correct dimensions.
All quickly done with a tool grinder and a lathe. And with the new gear, the Etalon is good as new!