Steel testing underway...

So I started on some real testing tonight, cutting Sisal rope and then testing sharpness against phonebook paper. With the first set of test blades there was a distinct point where it became clear the the edge was breaking down, this time it seems much fuzzier. It could be that I'm tired, but the blades seemed to just get progressively snaggier with each set of cuts, as opposed to staying good for a while and then starting to dull quickly.

I wouldn't read too much into that though, this test is very subjective, and the experience I'm having this time makes me wonder if there's something else I could/should replace it with.

To that end I prepared a LOT of cardboard strips ready for cutting tomorrow. Basically I'm just going to cut the cardboard using a small section of the blade until the blade is too dull to even cut any more without crushing the cardboard, then note down the number of cuts the blade made. I think this will be less subjective overall. I'd like to make the tests comparable to the first set if at all possible, but if it's not possible then it will just have to do.

I'm going to try the sisal rope and phonebook paper again as it worked well last time, but it wasn't meshing properly tonight so I walked away rather than forcing things. I'm sure we all know that trying to force something to work is a good way to get injured or mess something up!
 
Alright guys, I'm entertaining the idea that the second batch of test blades may actually be too hard, and that the edge breakdown I was seeing last night was because of micro-chipping.

The lack of visibility into the hardness of the blades is proving to be a bit of an obstacle, so I'm looking at possibly getting a rockwell tester into the shop by the end of the week. It was something I was planning on doing later on in the year, but all this has made me think of pushing the purchase up.

I'll keep you updated!
 
Very excited to see the results of the new batch. between your testing and Nathans test video I decided to give A2 a try.
 
I've been following this thread, thanks very much for sharing...

Aaron - idk how you did your initial sharpening after ht but for me, I consider 2x the depth of the initial micro-chip from the apex as bias due to decarb/post-ht-grinding-heat poor steel.
 
KalEl said:
Very excited to see the results of the new batch. between your testing and Nathans test video I decided to give A2 a try.
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I definitely think A2 is worth a shot if you've got the gear to heat-treat it. So far it seems like a really nice steel, and is quite easy to get in a wide variety of sizes.
 
bluntcut said:
I've been following this thread, thanks very much for sharing...

Aaron - idk how you did your initial sharpening after ht but for me, I consider 2x the depth of the initial micro-chip from the apex as bias due to decarb/post-ht-grinding-heat poor steel.
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No worries mate!

Not quite sure I'm reading your seconds paragraph correctly. I think you're say to remove steel for twice the depth of the initial micro-chip on the edge before you're getting a reasonably good shot at seeing 'good' steel?
 
So I've been looking around for advice on the optimum hardness for each of the different steels that I'm using, here's what I'm seeing so far:

Recommended hardnesses for hard use blades:
CPM154 - 58-59HRC
440C - 58-59HRC
A2 - 58-59HRC
CPM3V - 59-60HRC
O1 - 58-59HRC

I can tell you right now that it's quite likely that every blade in this batch is over 60HRC as they all skated my 60HRC hardness testing file with ease, which means these steels are not operating in their ideal ranges. That might well explain the strange snaggy edge failure that I was seeing during the sisal rope testing last night.

I'm not going to do any hard/destructive testing with the steels at this hardness. I might do some edge retention testing while I wait to get access to a hardness tester, then once I've worked out what hardness the blades are at, I'll likely temper them all back to their ideal hardnesses and then start testing again.

Does that all seem reasonable?

It really is a continual source of amazement (and fascination!) to me how involved all this stuff is, it would certainly be easy to lose yourself down the rabbit hole of heat-treatment!
 
aarongough said:
No worries mate!

Not quite sure I'm reading your seconds paragraph correctly. I think you're say to remove steel for twice the depth of the initial micro-chip on the edge before you're getting a reasonably good shot at seeing 'good' steel?
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Right, depth of micro-chip or rolled. I found this consistently true for many factory & most of my newb making (0 - 30's th) knives.
 
bluntcut said:
Right, depth of micro-chip or rolled. I found this consistently true for many factory & most of my newb making (0 - 30's th) knives.
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Gotcha. I don't think that's likely to be an issue as all of the blades were honed perpendicular to their edge to get the edges to be the same width before the initial sharpening. A decent amount of steel was removed from each blade (up to over 1/32" in once case as that blade was nearly a zero edge during HT)... Definitely a good thing to know for future blades though!

My theory about micro-chipping is just a theory right now, I didn't have a magnifier or anything at the shop last night to inspect the edges. I bought a USB microscope off Amazon today so that I have another tool to inspect the edges during testing. That should arrive tomorrow.

I've also arranged to pick up a Rockwell Hardness Tester from KBC tools on Friday. It's a bit of a pain in the wallet at this point to buy that, but I think it will really help me with ensuring consistency and quality across the knives I make in the future, and will also help diagnose exactly what is going on with this current batch of test blades.
 
This is definitely a rabbit hole. I think hardness is use specific. I do kitchen knives at 60-63 depending on the steel. I had a 15n20 blade at RC60 chip when the mother in law used a GLASS cutting board. :confused::eek:
I have an O1 chefs knife at 63 and no chipping, but it is used only on a good cutting board. I did a 52100 skinner at 61, and it will chip if you try to chop wood with it, but it slices leather like its butter. The edge is only .007 at the micro bevel. As soon as my rental sells, I am getting a hardness tester. Most of the general purpose knives are 58-60, and they seem to be fine. I haven't done a hard use knife though. I think there is a combination of geometry and hardness to take into account.
 
Willie71 said:
This is definitely a rabbit hole. I think hardness is use specific. I do kitchen knives at 60-63 depending on the steel. I had a 15n20 blade at RC60 chip when the mother in law used a GLASS cutting board. :confused::eek:
I have an O1 chefs knife at 63 and no chipping, but it is used only on a good cutting board. I did a 52100 skinner at 61, and it will chip if you try to chop wood with it, but it slices leather like its butter. The edge is only .007 at the micro bevel. As soon as my rental sells, I am getting a hardness tester. Most of the general purpose knives are 58-60, and they seem to be fine. I haven't done a hard use knife though. I think there is a combination of geometry and hardness to take into account.
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I definitely appreciate that hardness is use specific. I'm pretty sure that these blades are all WAY too hard for the kind of hard use I design my knives for. I'm actually kind of excited to see what the results of the hardness tests are, I think it will be quite interesting!
 
I was just wondering if your sensitivity and perception of blade cutting performance (of sisal, phone book etc) might be increasing and refining as you test, i.e that you are able to note more subtle changes than in the first round.

OTOH they could just be too hard and microchipping. Could you retemper them to take them down a bit?
 
ernestrome said:
I was just wondering if your sensitivity and perception of blade cutting performance (of sisal, phone book etc) might be increasing and refining as you test, i.e that you are able to note more subtle changes than in the first round.

OTOH they could just be too hard and microchipping. Could you retemper them to take them down a bit?
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That is a definite possibility! That test is pretty subjective unfortunately. I might well have just been having a bad day or something. I'll be getting that microscope today so I should be able to have a close look at the edges and see what is going on.

Tempering them down is definitely what I had in mind. Luckily all the blades are bare steel with no handles, so re-tempering will be fine!
 
Willie71 said:
I have an O1 chefs knife at 63 and no chipping, but it is used only on a good cutting board. I did a 52100 skinner at 61, and it will chip if you try to chop wood with it, but it slices leather like its butter. The edge is only .007 at the micro bevel. As soon as my rental sells, I am getting a hardness tester. Most of the general purpose knives are 58-60, and they seem to be fine. I haven't done a hard use knife though. I think there is a combination of geometry and hardness to take into account.
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Amateur dropping in, but ^THIS is what struck me. The 58-59 Rc range for O1 & A2 being the same as for 440C and 154CM seems too low as it takes away their advantage of >2X tougher - they should be higher hardness and be able to endure the same level of stress. Hardness is simply a measure of compression/bending resistance. However, there is a threshold geometry (i.e. thinness at the apex) where even light stress will exceed the UTS because the material support just isn't there! If the edge were thickened a just few thousandths and the apex kept at the same refinement, durability would noticeably increase without a very noticeable loss in cutting efficiency. Not so? It would be sad to use the tougher steels like O1 & A2 without highlighting that strength through increased hardness...
 
chiral.grolim said:
Amateur dropping in, but ^THIS is what struck me. The 58-59 Rc range for O1 & A2 being the same as for 440C and 154CM seems too low as it takes away their advantage of >2X tougher - they should be higher hardness and be able to endure the same level of stress. Hardness is simply a measure of compression/bending resistance. However, there is a threshold geometry (i.e. thinness at the apex) where even light stress will exceed the UTS because the material support just isn't there! If the edge were thickened a just few thousandths and the apex kept at the same refinement, durability would noticeably increase without a very noticeable loss in cutting efficiency. Not so? It would be sad to use the tougher steels like O1 & A2 without highlighting that strength through increased hardness...
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Absolutely, you make a very good point. The blades involved in the test were all 0.013" thick at the edge before sharpening, which is thin compared to the knives I make for customers (which are generally 0.020" thick), this is so I could push the steel a bit and see which steels would/wouldn't permit finer edge geometry. You might have seen from the last round of testing that A2 was totally fine with the thinner edge, other steels not so much. The extra toughness was coming into play there for sure.

I have to get a bit more information about the blades before I make any decisions on whether they should be tempered back. Firstly edge inspection under magnification needs to happen to see whether I'm actually getting micro-chipping, or whether I'm just being more sensitive in the test this time round. If I'm getting micro-chipping then I think that warrants the edges being tempered back. If not then I'll leave them as-is and assume that I'm perceiving the test differently.

EDIT: just realized I didn't respond to part of your post. Regarding thickening the edge to give more support. This will work for gross chipping, simply thicken up the edge and that blade becomes suitable for much harder use, but unfortunately if the blade is too hard it will definitely still see micro-chipping right at the apex. Idealliy I'd like to find the exact point where the edge starts failing by rolling instead of chipping and temper my knives to that point. If it rolls then at least it can be stropped back into shape, if it chips then it requires real sharpening to get it useful again...
 
aarongough said:
Absolutely, you make a very good point. The blades involved in the test were all 0.013" thick at the edge before sharpening, which is thin compared to the knives I make for customers (which are generally 0.020" thick), this is so I could push the steel a bit and see which steels would/wouldn't permit finer edge geometry. You might have seen from the last round of testing that A2 was totally fine with the thinner edge, other steels not so much. The extra toughness was coming into play there for sure.

I have to get a bit more information about the blades before I make any decisions on whether they should be tempered back. Firstly edge inspection under magnification needs to happen to see whether I'm actually getting micro-chipping, or whether I'm just being more sensitive in the test this time round. If I'm getting micro-chipping then I think that warrants the edges being tempered back. If not then I'll leave them as-is and assume that I'm perceiving the test differently.

EDIT: just realized I didn't respond to part of your post. Regarding thickening the edge to give more support. This will work for gross chipping, simply thicken up the edge and that blade becomes suitable for much harder use, but unfortunately if the blade is too hard it will definitely still see micro-chipping right at the apex. Idealliy I'd like to find the exact point where the edge starts failing by rolling instead of chipping and temper my knives to that point. If it rolls then at least it can be stropped back into shape, if it chips then it requires real sharpening to get it useful again...
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I missed it, what angle did you sharpen them to? That 0.013" edge thickness before sharpening means that they are thicker than that at the bevel shoulders after sharpening, but the slope to the apex will provide more or less support within the edge-bevel based on how thick the material is there. Since you need magnification to see the damage, it all occurred within that bevel, where the material is thinnest. A microbevel at the apex ground only 50% of the height of the damage within the bevel would provide more material support to the apex that may prevent any future occurrence under the same circumstances and would not require sacrificing edge strength via tempering. That is all I am talking about in regard to "thickening the edge" - just the minute portion/height of edge that is experiencing damage. You stropped the edges - any idea if the edge-damage exceeded the height of strop-refinement?

Again, I am only a consumer, not a knife-maker, but i have experienced 52100 @ 60 Rc and 15-dps that can chop-up hard oak with no detectable edge compression/rolling or micro-chipping. 15-dps doesn't mean a thick-edge, as that bevel angle need only be as high as the damage seen, maybe only 1/64" which gives an edge only 0.008" at the shoulder.

Not to deter you from your tempering and HT experiments, great work :thumbup: I'd just hate to see the strength in hardness sacrificed if a tiny alteration of geometry would suffice...
 
chiral.grolim said:
I missed it, what angle did you sharpen them to? That 0.013" edge thickness before sharpening means that they are thicker than that at the bevel shoulders after sharpening, but the slope to the apex will provide more or less support within the edge-bevel based on how thick the material is there. Since you need magnification to see the damage, it all occurred within that bevel, where the material is thinnest. A microbevel at the apex ground only 50% of the height of the damage within the bevel would provide more material support to the apex that may prevent any future occurrence under the same circumstances and would not require sacrificing edge strength via tempering. That is all I am talking about in regard to "thickening the edge" - just the minute portion/height of edge that is experiencing damage. You stropped the edges - any idea if the edge-damage exceeded the height of strop-refinement?

Again, I am only a consumer, not a knife-maker, but i have experienced 52100 @ 60 Rc and 15-dps that can chop-up hard oak with no detectable edge compression/rolling or micro-chipping. 15-dps doesn't mean a thick-edge, as that bevel angle need only be as high as the damage seen, maybe only 1/64" which gives an edge only 0.008" at the shoulder.

Not to deter you from your tempering and HT experiments, great work :thumbup: I'd just hate to see the strength in hardness sacrificed if a tiny alteration of geometry would suffice...
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I welcome all constructive criticism and ideas, so don't worry on that front! Yes you are correct the bevel shoulder will definitely we thicker than 0.013" after sharpening. I think the amount of support the edge gets near the apex is really determined by the sharpening angle, rather than the thickness at the shoulder, at least that has been my experience anyway. Gross chipping (large chips) is definitely influenced by the edge thickness at the should, but I can't imagine a mechanism that would allow the shoulder thickness to determine the amount of support the apex gets on a micro-scale (apart from the sharpening angle). Does that make sense?

The blades were all sharpened at 25º per side, which is a fairly robust angle that has done well on my other knives. You've got basically all the info that I have now, I'm open to suggestions if you think there's a sharpening refinement that might help!

I just got the microscope I was waiting for, it's a fairly cheap USB version, but should allow for a closer view to help see what's going on. Below I've attached some images take of the edge of my EDC blade (I'm still at work), these were taken handheld.

c11v5Ve.jpg

CX8R6Ip.jpg


Note again, that these are not photos of the test blades, just a quick test of the microscope. Once I get to the shop tonight I will be taking photos of the edges of the test blades.
 
Assuming these blades are at least 1/8 thick, 1.25 tall and ffg to 0.013. My quick est for 50* inclusive has bevel shoulder thickness ~0.015, bevel face width ~0.0178. That's quite a lot of supporting metal behind the apex for non-chop and non-lateral/deflection impacts... my 2cents.
 
bluntcut said:
Assuming these blades are at least 1/8 thick, 1.25 tall and ffg to 0.013. My quick est for 50* inclusive has bevel shoulder thickness ~0.015, bevel face width ~0.0178. That's quite a lot of supporting metal behind the apex for non-chop and non-lateral/deflection impacts... my 2cents.
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Yeah I agree. I've used the exact same edge geometry in the past (including during the first round of testing) and it has shown itself to be quite robust. I'm sure it could be tweaked, but I'm fairly sure that whatever issues are happening right now is quite likely to be an issue with the heat-treatment...
 
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