Edge Retention/Rolling Test Stand

[grepper]

Mr. Rick Kr uttered, "I have now read the entire thread and have learned a LOT.  Just as I was starting to get a clue about sharpening to finer levels of sharpness...   ...the world may be shifting on its axis.   I anxiously await results and further discussions."
 
Nothing like a settling down for a good read, eh? 
 
I have to agree.  While results at this point are preliminary and inclusive, they seem to be indicating some reconsideration of the durability of really sharp edges and how the various types of steel effect same may be in order.  But again, results at this point are preliminary and inclusive.

[KnifeGrinders]

My SET is ready to go, thank you Mike B. and EOU very much


First study is on edge stability/integrity (which is the ability to both take and hold a sharp edge) of mainstream knives, to determine the best edge angle as a function of sharpness.
The knife on the photo is a SWIBO professional meat processing knife, hardness Rockwell C 56-58 and 0.5% Carbon - similar to all those common kitchen knife brands like Scanpan, Victorinox, Wutshof, Zwilling Henckels... and I've got plenty of identical SWIBO knives for experimenting.

Basis for the study is there already, thanks to Cliff Stamp.
The conclusion that Cliff Stamp came to is that all things being equal, thinner is better up to about 8° per side, and 8° dps is usually as thin as it is practical to go - how low should the edge angle be depends on the steel.
Obviously, the lateral stability of the edge drops as angle decreases, and steels with lower edge stability require higher edge angles.
A well-known fact is that the edge stability of a steel increases with greater hardness and also as the Carbon content increases from 0.4% to 2%,
e.g. Global knives hold a sharp edge better than the brands named above even though they all have the same HRC of 56-58, but Global has more Carbon of 0.7%.

What we are to determine in this study is the best sharpness for the best edge angle for stainless steels with Carbon contents 0.45-0.5% and HRC 56-58, with practical implication to common kitchen & butchers' knives.

The plan is to test with SET these mainstream knives sharpened in the "very sharp" range of 50 BESS, 100 BESS, 150 BESS and 200 BESS for edge angles 8, 10, 12, 15 and 20 degrees per side.
A priory expectation is that at 50 BESS and 8° dps the edge  would roll immediately, but will show improved stability at a higher angle; we hope to discover best sharpness for the given edge angle from the edge stability point of view.

Overall I plan to do 80 test sharpening.
Shouldn't take longer than a week or two, will then start a new thread with results.
Will appreciate everyone's input if you have ideas for this run.

[KnifeGrinders]

EOU, could you tell us specification of the linear bearing used as the impactor/roller please?
Steel, hardness?

[EOU]

Well that's a fine looking machine KG! Mike here. Sorry for the delay but as I just explained to KG in an email, I've been recently afflicted with a case of Flesh Eating Ebola virus and that is as explained to my wife and nurse daughter and , of course, self diagnosed. I may live but not much longer in view of the fact that I have now managed to pass the disease on to my wife.

Don't know for certain KG about hardness of the bearing race. I would expect something about Rockwell 50 based on what I know about other bearing races. I also don't think that it makes much difference in this application because we got very similar results when using aluminum rollers. We decided to use steel only because we have a bunch of these bearings on-hand and, they seem to work. I think that you will see that the knife edge does not leave even the beginnings of a mark on the bearing surface.

I like where you're starting a bunch KG. Should be very interesting!

[KnifeGrinders]

I confirm that I've got your message, Mike.

Two checks have been agreed as checkpoints for all field testers:
sharpness score after 5 cycles (a checkpoint for “elastic deformation”); and
number of cycles causing "permanent rolling" when measured sharpness does not change any more (a checkpoint for “plastic deformation”).

Steel should be named, hardness if known, and the sharpening method.

There is one more value that we all should record: the Edge Angle
Edge stability clearly depends on the edge angle, and without it the SET numbers will have little meaning.

[KnifeGrinders]

I am half way with my research plan, meanwhile a video of the testing:
https://youtu.be/EdGOSWjrM0E

[EOU]

Thats a great video KG! Thank you very much for posting it. One note for followers of this thread; we've always seemed to work with taller knives that project above the top of the vise constraints. This allows a full 1.5" range of the roller over the test section of the knife. KG has gone to some effort to make certain that his knife blade is vertical and that is important. This compensating arrangement did result in a little less roller travel range for the knife tested. None of this affects the outcome of the test results, it just makes the test  easier to perform when the edge projects above the vise (In our experience anyway. Looks like KG did just fine). What we need to do is provide a better quality vise with the SET. KG made it work and work well but shouldn't have to go to the extra effort when testing lower profile knives. We'll say one thing for certain and that is that KG doesn't require any hand-holding  on new projects like this. He just dives in, identifies and works through the obstacles, and then performs the experiment perfectly. Great job KG! It's a pleasure to work with you.

We've got a little news of our own to report. We've purchased the 1/8th inch A2 steel and cut it into (12) 1.5 x 6.0" blanks. Today we are going to mill the 15° bevels on both edges of the steel and then send them off to Peters Heat Treat for heat treating. Thanks to a recommendation from Mark Reich, we have discovered Brad at Peters. He has been an invaluable source of information for us. Here's a picture of the A2 blanks:

   

So here is what is new with heat treating; we've decided to harden in 4 pt. steps from HRC50-62 rather than 2 pt. steps. We can always define things better once we learn what seems to matter and what doesn't. We'll be doing two sets of (4) 50 - 62 with a 15° double bevel and one set of (4) 50-62 with a single 30° bevel. 

Here's what new; we're going to sharpen the edges before we send them off for heat treat. Brad says this will work just fine and the heat treat won't even affect the sharpness level much, if any (in his opinion). This is huge if it works and for obvious reasons. This will clearly allow us to test the effects (if any) of the sharpening process on the steel with regard to rolling. We'll test for rolling straight out of heat treat and then re-sharpen the edge and test for roll again. Not only will we be able to test the effects of hardness on rolling but determine if the sharpening process affects it as well.

Should be exciting.

[Jan]

EOU, it is really an exciting experiment!  

Please let us know what is the heat treat impact on the blade sharpness level.

Jan

[Mark Reich]

I have to admit that I am very surprised to hear about sharpening before heat treat, but I would never bet against Brad's inclinations.

My experience would certainly run contradictory to the notion that it won't make much difference, but I doubt this is the first time Brad has hardened A2 blades that have been precisely sharpened and measured.

I don't use A2, but I know there are certain differences to it's optimal heat treat. This will be very interesting to say the least.

Mr. EOU, I would strongly suggest looking into a real precision sharpening system. The learning curve is shortest on a WEPS, and you will learn what it's like to create seriously sharp edges of exact angle. I think it could be extremely addictive to Mr. Grepper.

I would not evaluate the SET without the accuracy of a guided sharpening system, personally.

[EOU]

That's the way we see it Jan. If Brad is correct we'll be able to definitively segregate hardness from any potential effects of grinding. This we did not expect to be able to do so clearly. Stay tuned.

We're going to be interested in the effect on sharpness as well. Complicating this is the question of how effectively we'll be able to deburr the edge prior to heat treat. We won't mind using a plain leather strop on the edge after heat treat if it is beneficial. We just need to end up with a post heat treat edge in the 150-300 arena and then we can test.