CPM-M4 at low angles. My experience recently.

On blades like that made pretty thick behind the edge, I've always liked a shallow edge grind, maybe 8-10 degrees per side and a micro bevel of about 15 per side and probably switch to 20 per side when it gets too laborious to sharpen on the SM.
 
Scottie3000 said:
Holy crap, I've never seen that.
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One can normally sharpen straight razors in similar fashion. It was also more common practice to sharpen like that a few decades ago if you look at old hunting knives, slipjoints and for example my grandfather that still sharpened his knives like that. Not so common these days any more.
 
Silly Rabbit said:
Not meaning to hijack..for those who care my para 2, cts-xhp, has been brought down to an angle less then factory (sorry don't know exact angle) is experiencing minor chipping when pushed to harder use (minor landscaping tasks) it doesn't bother me though...talk about a toothy edge :rolleyes:
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If possible could you post a picture or two of the knife? I just finished sharpening my P2 in S30V to approx 10 degrees per side so we can compare the two and maybe get an idea of angle.
 
So even if down to 12 should I be seeing chipping with ctsxhp? Cutting the shaft of large dried palm leaves to remove the dead palms is when I think it happened
 
"should I be seeing chipping with ctsxhp" is actually a good question, but the use determines the angle still. If there was a small hunk of sand or other hard material in the stuff, yes, it will chip. I wouldn't re-do the entire edge profile around this small chip. Just chalk it up to experience & change the micro-bevel slightly, keep using it and you will eventually work through the chip area. I had this happen on a new ZDP blade, because I hit a staple which was hidden from view. It was annoying, but that's how it goes.
 
Silly Rabbit said:
So even if down to 12 should I be seeing chipping with ctsxhp? Cutting the shaft of large dried palm leaves to remove the dead palms is when I think it happened
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noseoil covered a few things, but one of the critiques of high wear steels:

- They offer no real advantage if you cut dirty material as dirty material can cause severe chips in the edge.
- Dirty material will dull (via edge rolling or chipping) everything, no matter the "super" you put in front of it.

IMO. That chip could have been an isolated event, you might not experience it again. It should be stable under 12 degrees per side. There are a lot of variables but I am surprised it chipped. I am just finishing up my P2 again at around 10 degrees per side. Last time I did that I got some interesting results, not what I was expecting, so its time to test again.

Here is an experiment of M390 at low angles.

Thin-edge-low-angle-M390-Para-2-how-low-is-too-low

You might find the following interesting related to steels and very low angles. It is done by metallurgist Roman Landes.

Knife Edge Diagram

Here is what he had to say:

Roman Landes said:
Dear Colleagues,

liked

http://www.schmiedecafe.com/forum/attachment.php?attachmentid=83

The following is also a good idea about Edge Stability:

http://www.smt.sandvik.com/en/products/strip-steel/strip-products/knife-steel/knife-steel-knowledge/

You will see there are pictures that show a fine micro structure steel like 12C27 compared to 440C.

you find a PDF download in english as one of my latest works, in steel & knife research ongoing in Germany.
To introduce myself I am knife maker and damascus smith since 1987 in Germany. My profession is graduated engineer in Automotive engineering and Material Science. Meber of the German Knifmakers Guild sinc 1993.

I am also author for the German Book, Messerklingen & Stahl (M&S) Technologische Betrachtung von Messerschneiden (Knife blades and Steel, A technological survey on knife edges © 2002 Wieland Verlag, Bruckmühl, Germany) witch has successfully established a high quality discussion base on scientific research towards knifes and steel. The base of the Book was developed in the early 90’s when I was in my studies.

With this download, you get a little goodie, extracted from the upcoming new book Messerklingen und Stahl, Praxishandbuch der Stähle (Knife blades and Steel; The Practical Handbook of Steels © 2005 Wieland Verlag, Bruckmühl Germany)

What is the download about?
The download shows the so-called “model of the cutting edge” taken from (M&S©2002).
The actual book will show around 50 commonly known tool steels/ -alloys used for knife applications (e.G. ATS 34, 52100, RWL 34, L6, Vascowar, M4,…) an the way to treat them according to this application.

Furthermore, one will see the abilities of the steel used supporting qualities essential for knife application (e.g. edge holding, wear resistance, sharpen ability, cutting ability, cutting edge stability, corrosion resistance,…), SWOT- Analysis…

The model of the edge provided here, shows 5 selected reference alloys commonly known in the worldwide knife society.
· 1.4125 (440C) Reference for traditional stainless steels
· CPM S90V Reference for modern stainless PM-steels
· Talonite Reference for Chrome Cobalt Alloys
· 1.2510 (O1) Reference for hypereutectic tool steels
· 1.2379 (D2) Reference for 12%-Chrome Cutting Steels

What Do you see?
What you see is the 1000x magnification (means all at the same scale) of the inner structure (microstructure) of this alloys, shown as micrographic pictures, in heat treated condition (Austenizing, Quench, Cryo, Temper in multiple cycles; except Talonite) Etching: Beraha 1.

The white spots, are the so-calles Carbides responsible for the wear resistance in a alloy of this kind (The Teeth), surrounded by the Matrix (Meat) (Martensit, except Talonite)

The sheet is designed to get folded on the edges marked. What you get when you do so, is the model of the edge 1000x magnification in 3D. By using the scale of the angel (Adjust in back light with single print) you can adjust every edge geometry between 15° and 90° edge angle.

This means, having the model in 3D in front of you and assuming there is a local limited load applied from a side force towards the edge (occurs constantly in the normal use of a knife), this force will deflect the edge and in dependence of the load, and the steel can take, the edge will draw back in line or chip locally (wear and loose edge).

The carbides will play a major role in the behavior of the steel in the edge
Since they are very hard and brittle, in a fine cutting edge, carbides are the first point to start with chipping, especially when the are to many in relation to the surrounding (meat) or the carbides are so large, e.g. when they will fit nicely into the full range of sharp and dull limits1)

Note, the large carbides of the alloys shown, will by no means get any significant change in size, during the complete heat treatment cycle (except 01, if hardened at to high temperatures, the carbides will dissolve completely and a mess of retained austenite and coarse brittle Martensit-grain will be there).

What you can do with it now?

Taking into account, that a sharp edge1) is around 1µm on the tip and a dull one1) is around 10µm in width, if a critical load to the edge is applied (wear of the edge), the different alloys behave different at different angles adjusted.

Print the download (use A4 for the print-format), fold at the 3 lines marked and start adjusting the angle.

I am sure this will help, to explain something…

...and hopefully start discussion …

Best regards Roman
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Original thread:

http://www.bladeforums.com/forums/showthread.php/344902-Edges-and-Steels?p=3043379#post3043379

Here are also some definitions and you can see the difference between a knife steel such as 12C27 and 440C in microstructure at the edge.

http://www.smt.sandvik.com/en/products/strip-steel/strip-products/knife-steel/knife-steel-knowledge/

To state my approach to knife sharpening:

- Lower the angle as far as possible
- Test
- Inspect
- Modify the edge to support my needs.

Ewerstruly did some experimentation with how cutting performance is increased by lowering the angle. Look at this Part 1 of 3.

[video=youtube;u4rDIFFyXVk]http://www.youtube.com/watch?v=u4rDIFFyXVk[/video]
 
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Marthinus, I for one at least have interest in some of the finer points of performance .I wonder if Roman has written of these . Toughness -fractures of coarse carbide steel is usually from carbide to carbide . In a fine carbide steel such as the CPM or other 'powder steels' the fracture goes between the carbides .That means better toughness. Another is the presence of cohesion [ a strain field surrounding a precipitate ] We can see the strain field with an electron microscope . This is part of the 'secondary hardening of tool steels at about 900 F. This is also part of cryogenic quenching .There is still much to learn about cryo .But in any case cohesion is destroyed by improper tempering.
I wondered if steels like CPM M4 is available from dealers or does a maker order direct from here from dealers like the SteelBaron ?
 
mete said:
Marthinus, I for one at least have interest in some of the finer points of performance .I wonder if Roman has written of these . Toughness -fractures of coarse carbide steel is usually from carbide to carbide . In a fine carbide steel such as the CPM or other 'powder steels' the fracture goes between the carbides .That means better toughness. Another is the presence of cohesion [ a strain field surrounding a precipitate ] We can see the strain field with an electron microscope . This is part of the 'secondary hardening of tool steels at about 900 F. This is also part of cryogenic quenching .There is still much to learn about cryo .But in any case cohesion is destroyed by improper tempering.
I wondered if steels like CPM M4 is available from dealers or does a maker order direct from here from dealers like the SteelBaron ?
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Mete, you ask some interesting question and provide some interesting comments. I have moved away from studying steels in depth, but I do hope that someone will build on Romans work.

As for the availability of CPM-M4, I know one can source it from Niagara, or what is locally here in South Africa easier to obtain is Bohler's S693 Microclean.

There is a local maker that has build him a few folders out of CPM-M4 and has experimented with the secondary hardening, deep freeze (not cryo to my knowledge, but under correction), low tempering temperatures vs higher tempering temperatures and he loves it at the secondary hardening area. Will not make for any clients though as the care and maintenance on the blade he feels can cause problems for a lot of people. It is interesting to see him use it as a deburring tool on hardened D2 plates and aluminum blocks though.
 
If the blade had a better geometry that was suited for a very low edge angle the performance would be much better. The GB example in this thread has a very wide secondary bevel which in my experience causes a weak edge because the sharpened bevel thins out too much behind the apex. You also have an incomplete scratch pattern leading to the apex as seen in the up-close shots, you can see coarser grind marks under the finer grind marks and on an edge this thin this can cause stress risers which will lead to chipping at the apex.

Thanks for the write-up though, it's always nice to see someone pushing the limits.
 
^ Thanks all.


Jason B. said:
If the blade had a better geometry that was suited for a very low edge angle the performance would be much better.
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What geometry do you feel would suite the low edge angle performance better?

Jason B. said:
The GB example in this thread has a very wide secondary bevel which in my experience causes a weak edge because the sharpened bevel thins out too much behind the apex.
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That was one of the hypothesis behind the test, however, adding to your point below

Jason B. said:
You also have an incomplete scratch pattern leading to the apex as seen in the up-close shots, you can see coarser grind marks under the finer grind marks and on an edge this thin this can cause stress risers which will lead to chipping at the apex.
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I have run similar experiments on my Des Horn Imvubu in Nitrob-77 (if you google you will find my long review on that knife with videos showing me using it as to scrape etc), hollow ground, but it was thinner than the GB (as stock) with no fracturing of the edge running similar experiments. Only rolling of the acute edge took place, but the steel was designed and heat treated to roll rather than fracture.

Here are the now reground GB and Imvubu. (Note, the test in this thread was back in 2013 when I was experimenting with pushing different steels to the point of failure for my own interest).

IMG_3197_zpsazae4tqe.jpg


IMG_3198_zpsqnxx7wjl.jpg
 
The geometry I speak of I see you have already done. Simply thinning down the blade is all that is really needed, it lowers stressful forces on the edge apex and because the bevel is smaller the angle is more consistent from apex to shoulder. Large bevels like it originally had tend to taper too much before the apex, much more than the same sharpening angle on a thinner blade. I'm sure that GB is a stellar performer as it is now.

Your comments about the Des Horn reinforce this thought.

(I noticed the thread was older, nice to see it come back up though)
 
Jason B. said:
The geometry I speak of I see you have already done. Simply thinning down the blade is all that is really needed, it lowers stressful forces on the edge apex and because the bevel is smaller the angle is more consistent from apex to shoulder. Large bevels like it originally had tend to taper too much before the apex, much more than the same sharpening angle on a thinner blade. I'm sure that GB is a stellar performer as it is now.

Your comments about the Des Horn reinforce this thought.

(I noticed the thread was older, nice to see it come back up though)
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I'm not much of an expert but I find that I prefer originally thinner blade stock with "more sane" bevel angles than thicker stock beveled with really low angles...
 
Jason, Chuck,

I don't get it.

For same final apex bevel, say 12° per side. On thicker blade (primary grind) this results in wide bevel, say 0.4" before it transition to the primary grind. At this point, the shoulder thickness is say 0.03". If the primary is thinned down so this bevel now is only 0.1" wide, the thickness right behind the new shoulder is same as old bevel when bevel width is 0.4". However, the stock (now new primary grind) at 0.4" from apex is thinner (assuming 0.02") as it's now the new primary grind after being thinned down.

Why it is now better handling the chipping by lateral forces with less material at say, 0.4" from apex?
 
I understand it as follows, please correct me if I'm wrong:

- Knife 1 is thick behind the edge, so it has wide bevel shoulders.
- Knife 2 is thin behind the edge, so it has narrow bevel shoulders.
- Both knives are M4 at the same hardness and heat treat and grind.
- Both knives are sharpened to 30 deg incl with the same edge finish.
- Let's say you are making long straight slices through thick cardboard.

Knife 1 will have a certain amount of friction in the cut, so will require you to use a certain amount of force to make the cut.
Knife 2 will have less friction than Knife 1 in the cut because it it thinner, so will require you to use less force to make the cut than Knife 1.

It is very likely that you are not able to make perfect 90 deg cuts into cardboard throughout your whole cut. When you stray from 90 deg, you create lateral load on the edge. When this happens with Knife 1, you are likely to put more lateral load on the edge because you are using more force than doing the same task with Knife 2. So Knife 1 is more likely to chip/wear at the edge than Knife 2, even though it is thicker.

I'm sure the above only applies under certain cutting conditions, because when you go for full-on prying or scraping, the thinner knife should fail before the thick one.
 
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