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MaxaMet - McCullen

Posted by CliffStamp 
MaxaMet - McCullen
August 17, 2014 04:25PM
Intro : [www.cliffstamp.com]

This is the standard mule pattern, see Jeremy's video's for many details. To start I needed to sharpen the blades, I started with one of the ones which is optimized for toughness (the softer one at ~64 HRC). This is how much of the blade was left to zero :



I asked Jeremy to grind it as close to zero as he felt comfortable, as you can see there is very little metal left at the edge. However it took three thousands passes per side, six thousand passes total to zero the blade with the Bester 700 waterstone. The bevel is now full zero at approximately 7.5 dps and again this is the Maxamet mule which is easy to grind.

This steel/hardening really is too much for the Bester which gets slick and wears down and doesn't release abrasive well, but of course it isn't made to grind this steel, in fact not many stones are given the extremely high carbide volume and ability to reach extreme hardness levels (~70 HRC).
Re: MaxaMet - McCullen
August 17, 2014 05:38PM
Wow. Are you going to use something like the sigma to sharpen these knives?

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Re: MaxaMet - McCullen
August 17, 2014 05:46PM
That seems fairly in keeping with what it has taken to do a similar amount of work with other high carbide steels.

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Re: MaxaMet - McCullen
August 18, 2014 06:19AM
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Bugout Bill
Are you going to use something like the sigma to sharpen these knives?

This would be practical, but I want some numbers for relative performance in the cardboard chart. I did the 69 HRC one as well, it is much harder to grind again, so much so that the Bester 700 just went slick and a thousand passes makes no difference even under 50X magnification. I has to use the Task Garden stone (which is extremely coarse << 200 grit) to apex it and then do 500 passes on the Bester to just plane down the coarse scratches.

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Mark a
That seems fairly in keeping with what it has taken to do a similar amount of work with other high carbide steels.

The grindability would be expected to be similar to A11, S125V etc., the 69 HRC one is very similar to the 70 HRC 121 REX.

It is much lower than Elmax which grinds easily in comparison, just look at how much curvature had to be taken out after the Washboard sharpening and how fast that was done in comparison to the tiny amount in the above.
Re: MaxaMet - McCullen
August 18, 2014 03:22PM
I did a cardboard run on one of the 64 HRC ones, it was ok but not impressive (5% was about 25 m, that is in the Type I class). The edge tended to chip :



+



However cardboard is very random and there are a few other issues. The first concern is this is what the edge looks like off of the Bester 700 :



Because it takes so long to sharpen this (it took 1000 passes per side, 2000 passes total just to sharpen it against after the cardboard cutting) it complicates not over grinding which is all that is shown on the edge shot above.

However given that edge is what proceeds the final 600 DMT micro-bevel it might explain the early blunting as it would accelerate fracture). Ideally the edge would be formed with a much finer stone to minimize that damage at the apex.

The other part is that at the end while it is much blunter than when it starts (< 1.5% of the initial sharpness) most people are likely to not consider it dull because :

-you can barely see light reflecting at all, very faint line
-it can still cut 3/8" sisal with 11-12 lbs (3/8" hemp is less, but it can depend on the rope)

Many people don't even achieve a 11-12 lbs cut before they start any edge retention trial. The problem is for a lot of people, even though I am cutting to what I consider very low sharpness, for some people the ratios calculated may not be representative for edge holding.

I need to think about this a little because I believe if you :

-cut to extreme levels of dullness
-use a lot more force in cutting

then the UHC steels may have a different ranking. The problem is actually evaluating it in a quantitative manner and of course doing the amount of work it takes to reach that point. I believe you are looking at ranges of 1 - 10 km of cardboard cut. Of course the question then becomes is that even a practical number assuming you can generate it because outside of doing very controlled stock testing, how likely is it that you can cut 10 km of cardboard without the blade getting damaged by accidental impact?

Many years ago I came to the conclusion that for wood chopping blades edge retention made no practical affect as most people discussed it. Yes I could measure a difference but practically that difference would never be of consequence. While I could do stock cutting easily on clean woods, as soon as I did actual work the edge always blunted by damage, never slow wear. I rapidly came to the conclusion that any even decent blade could chop 100 pieces of 2x4 and still cut light grass -but- I could never cut that much wood without hitting something like a piece of dirty bark so what difference did it make if a blade could do more? I quickly realized that it was more important for the blade to be easy to grind, very tough and hard to minimize damage in accidental impacts.

Still though, it can be interesting to measure it, just realize what it is being measured and what effect it makes (or doesn't) in actual use.
Re: MaxaMet - McCullen
August 19, 2014 01:08PM
I reground the other two, the times were similar, however this was interesting :



This is from forming the edge with the Task Garden hone which is extremely coarse. Note how the fracture actually undercuts the steel. I am wondering if the coarse finish from the Bester 700 is compromising the edge retention of the very high carbide steels by a similar, though obviously less extreme extent. I think I will try some where I use the Naniwa Aotoshi 2k Green after the Bester 700 and see if it makes a significant difference.
Re: MaxaMet - McCullen
August 19, 2014 05:51PM
I did a run with a 69 HRC one which had been apexed by the TASK hone. Now parts of the edge looked like this before the 600 DMT micro-bevel :



However most of the edge (90%) was fine after the 600 DMT micro-bevel:



However the edge retention is lower than with the 64 HRC one. Now I want to repeat this a few times, but I have seen this many times before on other steels (121 REX). I think what is happening is that these UHC edges are chipping at the very apex leading to premature wear. The first thing I want to check is make sure that the prep work isn't causing it so I am going to finish the edges like this before the 600 DMT bevel :



This is with the Naniwa Aotoshi 2k : [www.cliffstamp.com] . If this fails to bring out the performance I am going to increase the edge angle and radically increase the finish and see if that stabilizes the edge.
Re: MaxaMet - McCullen
August 20, 2014 12:56PM
did you get a new microscope Cliff?

This is great info/research...thanks!!!

question: in that pic above that you sharpened w/ the task hone, are those chunks missing out of the edge 100 microns wide?! from the hone? that's crazy! Also, when you refine the edge w/ a higher grit (like the 2k) aren't you sacrificing the toothiness?
Re: MaxaMet - McCullen
August 20, 2014 01:55PM
Quote
razoredgeknives
did you get a new microscope Cliff?

No, I was going to get a metallurgical one, but they simply don't have the resolution to see the critical issue which is the form/function of the apex. I am playing with the idea of a SEM, but I really would need to build a dedicated clean lab for that.

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question: in that pic above that you sharpened w/ the task hone, are those chunks missing out of the edge 100 microns wide?! from the hone?

Yes, they are 0.1 mm, you can see it by eye. The stone is extremely coarse (as in you can see the abrasive grits easily by eye) : [www.cliffstamp.com]

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Also, when you refine the edge w/ a higher grit (like the 2k) aren't you sacrificing the toothiness?

Yes. To be clear I am not saying that the cutting ability will be higher at the increased polish just that the edge retention maybe. It is just an idea. I know it is true for ceramics, you can't use them with a coarse edge, it has to be polished or they fracture too readily and the edge retention is too low. I think there is a critical point for steels and when you go above it the same thing happens. But at this stage this is a really low confidence hypothesis only.
Re: MaxaMet - McCullen
August 28, 2014 04:50PM
I did another run with the 64 HRC (A) one, the performance was similar in how it behaved :

-light chipping, infrequent
-very minimal reflection of light at the end of the cutting



That is straight down into the edge which is about 10-20 microns thick, I can just barely see it in sections (light reflecting from it). The Naniwa Superstone 400 does a very nice job of sharpening it :



That chip is a left over from use on the cardboard, the edge forms really clean. Not as polished as the Naniwa 2k (which is almost mirror) but the edge line is almost as crisp which is very interesting.
Re: MaxaMet - McCullen
August 30, 2014 03:56PM
Here is one of the 69 HRC ones with the Naniwa Superstone 400 finish :



Not as fine as the Naniwa Aotoshi 2k but this is very nice/clean without any burr minimization and very decent speed. Ok it is decent for Maxamet and for a very wide bevel, it is still ~1000 pps.
Re: MaxaMet - McCullen
August 30, 2014 05:29PM
Cliff,

Even though I ground the blades pre and post HT with coolant the blades took a lot of grinding to make them. Do you think the blades suffered any heat damage?
Re: MaxaMet - McCullen
August 30, 2014 05:40PM
I don't think so, it is going to be awhile before I really reach any firm conclusions from them as the TASK stone did a lot of damage to them in the regrinding.
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