I wanted to confirm the hardness of some steel that I was about to machine, and remembered that a few years back I had acquired this instrument. At the time I could get neither rhyme nor reason out of it - everything seemed to be stuck - no dial movement - so it has just sat in a cupboard awaiting 'the right time'
Well that time came the other day - it needs to perform!
Housed in a beautifully made pair of boxes it has many accessories and must have been a very expensive instrument in it's day. It has perhaps suffered from slightly damp storage as there are signs of corrosion in places, and as I say the dial wasn't moving at all.
So - how is it supposed to work? There is a tiny very hard spherical surface on the end of a probe that projects through an encompassing shroud. The shroud comes into firm contact with the sample, and the ball is pressed into the surface of the work. The rest of the instrument is dedicated to ensuring that the pressure applied is constant, and to the measuring of the differential movement between the probe and the shroud.
Now I confess that I took no photographs of it dismantled - sorry but bits were everywhere and my main concern was remembering how to put it all back together!
Internally there is a rather complicated differential balance arrangement and large spring, and the rear end of the probe rests on a piece that turns the motion through 90 degrees and passes it to the very sensitive dial gauge. The gauge is directly calibrated in the units of hardness that you have selected by fitting one of three dials that are supplied, along with three spherical ball probes each appropriate to the selected units.
The main issue was that the extremely sensitive dial gauge was jammed fully deflected, and general build up of crud on the internal springs and levers. I only had to dismantle and re-build it four times before I got it right, so sorry I'm not pulling it apart for a photo session!