Measuring Rockwell C with Superficial Tester

So I found myself needing to measure hardness (Rockwell C) on a few parts, but i dont have a 'Rockwell C' tester. I did happen to find (believe it or not, it was up on a shelf) a superficial hardness tester (Rockwell N, T and Vickers).

I did a little research, and found the conversion tables. I need to measure up to 60Rc, and it looks like i can do that using the R30N scale.

My question is, will it really work?

If my understanding is correct the 30N is essentially the same as Rc, but with a different weight, therefore a different depth of indentation. Im not measuring rocket components, if im off a point or two, ill be OK.

Thoughts?

Do you have any "C" test blocks? That would tell you if it's reading correctly.

Didnt think of that I think i might. Thanks!

I had both a superficial and a Rockwell tester. You can find conversion tables that will convert between scales but they all come with a lot of cautions about accuracy. I've tested on superficial scales and then tested the same part on the C scale and in most cases found them reasonably accurate. I have found that the superficial scales are influenced more by surface finishes than the heavier scales, which makes sense. If it was me and I was testing on a part that had nice surface finishes I'd use the heaviest superficial scale, so 45N, and be reasonably confident that I'd get a decent result.
Also goes without saying that you would need a test block to set your superficial tester to in order to verify it's accuracy. I've never done or seen anyone use a test block marked for one scale to set a tester on another scale. It might work I've just never seen it done. So use a 45N block to set your machine to inspect at 45N. Also you should use a test block that is in the appx. hardness range of the parts you're going to be inspecting.

If you're sure the heat treating process has through-hardened the piece, the superficial test might be OK.

The lower pressure of a superficial test is meant to measure a case hardened piece. The penetrator won't get deep enough to tell you if that case reaches a reasonable depth.

+1 on using the heaviest pre-load and sharpest penetrator your superficial tester will do.

Tested it out today. I had to buy the correct indenter. I did find the correct calibration sample too, so I checked that out. Yep, it works. At least, well enough for my purposes. I had a sample that was previously tested on a HRc machine, with the charts, it converted to within one point of hardness.