Structural Edge Testing

[subwoofer]

Hello All, I seem to have been away a while, and may not be up to speed with the latest on the SET.

I did try a couple of searches for 'Structural' and 'SET' but didn't find what I thought might be some more established threads on this (please point me at them if I missed them).

How has everyone ben getting on with their SETs? Are there any tweaks, or hints for getting clear results?

If I were to summarise my own findings I'd say the first challenge is the consistency of the testing edge. My results are showing inconsistencies which I am sure are due to the consistency of the edge from test sample to test sample.

So far I find that unless an edge exhibits chipping, I can virtually guarantee that I can strop the test area back to a sharpness either identical or often better than the starting sharpness (although usually there is a visible sign of the testing site).

It feels like the results I have so far don't quite match with expected performance, so I'm questioning the value of what I've done so far.

I've got some blades incoming where I would like to show a clear difference with the SET. With a 58HRC and 64HRC version of the same blade there should be a significant observable difference.

What is the current thinking on this?

[Mike Brubacher]

Good to hear from you Subwoofer! The bottom line is this - SET testing indicates that all steel edges roll and that the hardness of the edge, at least up to HRC 62, makes some but not significant difference in the result.  It is possible, however, that we were using a sledge hammer to crack an egg in the testing that was conducted by yourself, ourselves and others around the world. Even though only 150 grams of force was applied to the edge, in consideration of the thinness of the edge, 150 grams may have been too much. Perhaps a much lighter impinging force would yield test results with a greater spread between the various HRC hardness levels. 

Our tests showed that stropping/steeling could return the edge to at or near it's previous sharpness readings, as well.  Any butcher, a hundred years ago, could have told us that, however. To us, this simply proved that the edge had been rolled as opposed to damaged during SET testing.  Yes, there is a lot of variability during the sharpness testing phase of SET testing. I guess that's just the nature of beast due to uneven rolling of the edge along the test area.

Cheers and a happy holiday to you and our customers in the UK!

[KnifeGrinders]

Of recent, SET helped us determine the best edge angle for knives of "supersteels".

Full report: What Edge Angle is good for Supersteels
Video of the SET experiments: https://youtu.be/WC3oVIKhlMs
Video of the data and conclusions: https://youtu.be/eqjgeWcsHEI

SUMMARY
We have done a research sharpening knives of tool steel, “supersteel” of hardness HRC 60, and "superhard supersteel” of HRC 70 at 10, 11, 12, 13, 14, 15, 17 and 20 degrees per side and testing edge stability of each of these edges.

The best edge retention in conventional tool steels like D2 or K110 shows a 15 dps edge.
In “supersteels” the best retention has a 12 dps edge;
and “superhard supersteels” of HRC 65-70 hold well a 10 dps edge.

Please note, that we sharpen such steels only with CBN and diamonds from start to finish.
The same steels, but sharpened with conventional abrasives, will have a less stable edge, even if sharpened at 20 dps.