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Ernst Hartepruffer Hardness Tester

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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!

So what were the results?

My EN19T billet destined for a chuck adaptor is 275 Brinell

My EN8 dummy A2-5 nose piece is 225 Brinell

My test piece for deep hole drilling is 143 Brinell

My Kurt vice surface is 180 Brinell which I find surprisingly low

I also found that trying to do two tests in the same spot is pointless - the dent is already there !!!!!!!

Altogether a satisfactory conclusion, I just wish I could remember who I got it from - it was possibly Home Workshop sales / or maybe sales on this forum or even conceivably eBay. I remember that the nice gentleman delivered it so if you are that person please put your hand up!

Hi Andrew,

I'm enjoying you making a meal out of this adapter!

Cheers, Matthew

I'm waiting for some HSCO 22 mm end mills to be delivered before I start Matthew and rather a lot of 'other stuff' has got in the way recently  :bang:

Sorry Andrew, but I have spent many frustrating hours sitting in a constant temperature controlled room, but your results are almost worthless. The immediate reason being that you do not report the temperature of each piece. The items to be tested and the instrument and its testing 'probes' must all be at the same temperature throughout which usually means art least 36 hours preferably 48. it was a surprise to me to find that the rate of cooling and heating of various materials was so varied.
Brinell may have been very popular because of its simplicity but there are much more reliable instruments where inter instrument variation is far less. Vickers combines operational straightforwardness with fair consistency but Knoop is by far the most accurate in my experience but almost the most wearing on the operator. An hours listening through the headphones could drive you mad.

Anyway I wish you luck and a good supply of your favourite tipple in understanding your results and what's going on. This is the sort of evaluation which it is worth farming the tests out to Teddington ! I spent at least 6 years on these tests and  never want to go near any lab that does them in house again.



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