Clark Rockwell Hardness Tester CR8

Jim Rieck

Jim Rieck

Joined
Jun 4, 2010
Messages
71
I just purchased a used Clark CR8 hardness tester. The calibration is a bit off due probably to shipping from Ontario. The diamond looks good under a microscope. I have a 61.5 +- 0.5 standard and have been getting 5+ points on the HRC scale with my testing. Does anyone know how to calibrate this thing? The manufacturer is overtly mum about giving me any information about it and all I want to do it see how my heat treat methods are doing. Anyone out there calibrate themselves?
 
Sorry I can't supply a calibration procedure. Suggest you get a list of the companies who sell the model you have and contact them. They may be able to help you out.

Jim Arbuckle
 
Thanks Jim. All roads seem to lead back to Sun-Tech Corporation in Michigan. They own Clark and a couple of other related companies. I talked to them and they told me that the calibration procedure was proprietary. I was a bit taken aback, but doing further reading I am finding out that in industry, hardness testing accuracy is a very ticklish thing. Sun-Tech wants to keep as much control over their instruments as possible, I guess. That is why I came to this forum asking if there is anyone out there doing their own calibration on Rockwell hardness testing bench top instruments. The instruments are really quite simple (though heavy) and I can see some places where adjustments can be made. If no one really does their own and I have no other choice I will likely just disassemble the thing, see exactly how it works, and figure it out (or break it). More at 11:00.
 
I work at a calibration lab that does them, but I'm not the resident expert on them, but...
You should be able to turn the bezel of the indicator so it reads spot-on.
This will not tell you that the preload and load forces are right, or if the readings are correct over a large span of readings, but it should be okay within a few points.
Get another hardness standard within the range you want to be checking, and if both will read correct, then no other adjustments need be done.
If it doesn't look good at one of the readings, then other adjustments are required.
It may seem simple to just take it apart and figure out how it works, but I know it isn't...:confused:
 
You could always test a few blades on your tester and then send them to someone with a calibrated setup, and then adjust your results according to the readings the other party got.
 
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