CPM-M4 in the Gayle Bradley

[alucardje]

Hello Guys;



While trying to figure out how to best sharpen the Gayle Bradley, I've found some things that are probably good info for more people.


1. Altough mine is JJ; and there has been some talk of bad hardening in that batch; I think the hardening is done Good; maybe some blades that have surface decarburization, mine had it a little. (see other thread, search gayle bradley JJ).

2. I was sharpening on a Trizact A6 (about grit 2500) belt - as usual - and I couldn't raise a visible bur. I felt it a liiiitle bit, but I couldn't see a bur. On softer conventional steels, I would have made a huge bur. Now is this steel really harder or is there something else going on?

3. I switched to a trizact A45 (about grit 400) belt - I usually use this belt to create the cutting on freshly finished blades. I could raise a bur with this, but noticeably slower and a smaller bur then on other steels.

4. Polishing; from my point of view a very good corrosion-prevention, and for me very repeatable, just hold it against the wheel again. However; this blade doesn't polish at all. You can make it reflect more then the factory finish, but you cannot mirror polish it.

Strange. You can make it really sharp, but it doesn't bite (polished edge). Then I compared it to CPM-440V (my old military), S30V (my new military), CTS-XHP (manix 2), CTS-30BD (manix 2), M390 (benchmade AFCK).

Of all the things, I found S30V along with XHP to be the "softest" steels; CQ raising the biggest burs. CPM-440V hardly raises a bur, but whatever bur is raised, it's very coarse. CTS-30BD raises a slight bur, but knocks off very difficult giving the impression it's a very damage resistant steel. M390 raises the smallest bur, probably because it's that hard, but the bur is still double the size of CPM-M4. I usually listen to my feelings about a steel; and harder steels that aren't chippy, I usualy make the edge thinner. As such, the CPM-M4 was the thinnest edge (30°), CPM-440V (40°) was the thickest.

After that, I did some cardboard cutting (next week monday is paperday). Pretty much always cut agains the folds, and there was a lot of the same quality cardboard.

Judging from what I saw during sharpening, I kept cutting till the knife stopped clean cutting paper (I tested after each 5 cuts).

Altough the full flat grinds cut better from the start, after a while the geometry stops to matter, and the edgeholding of the steel starts to matter.

General order:
S30V => 40 cuts
CPM-440V => 45 cuts
CTS-XHP => 60 cuts
CTS-30BD => 65 cuts
M390 => 65 cuts
CPM-M4 => After 80 I stopped; it still cut paper cleanly, it just didn't feel sharp anymore.

Overall; very impressed with the CPM-M4 in the gayle bradley. To me; it begs for a thin edge, and it is by far the hardest steel in the test batch of high-end steels. It actually makes S30V look bad :)

[jackknifeh]

Hello Guys;



While trying to figure out how to best sharpen the Gayle Bradley, I've found some things that are probably good info for more people.


1. Altough mine is JJ; and there has been some talk of bad hardening in that batch; I think the hardening is done Good; maybe some blades that have surface decarburization, mine had it a little. (see other thread, search gayle bradley JJ).

2. I was sharpening on a Trizact A6 (about grit 2500) belt - as usual - and I couldn't raise a visible bur. I felt it a liiiitle bit, but I couldn't see a bur. On softer conventional steels, I would have made a huge bur. Now is this steel really harder or is there something else going on?

3. I switched to a trizact A45 (about grit 400) belt - I usually use this belt to create the cutting on freshly finished blades. I could raise a bur with this, but noticeably slower and a smaller bur then on other steels.

4. Polishing; from my point of view a very good corrosion-prevention, and for me very repeatable, just hold it against the wheel again. However; this blade doesn't polish at all. You can make it reflect more then the factory finish, but you cannot mirror polish it.

Strange. You can make it really sharp, but it doesn't bite (polished edge). Then I compared it to CPM-440V (my old military), S30V (my new military), CTS-XHP (manix 2), CTS-30BD (manix 2), M390 (benchmade AFCK).

Of all the things, I found S30V along with XHP to be the "softest" steels; CQ raising the biggest burs. CPM-440V hardly raises a bur, but whatever bur is raised, it's very coarse. CTS-30BD raises a slight bur, but knocks off very difficult giving the impression it's a very damage resistant steel. M390 raises the smallest bur, probably because it's that hard, but the bur is still double the size of CPM-M4. I usually listen to my feelings about a steel; and harder steels that aren't chippy, I usualy make the edge thinner. As such, the CPM-M4 was the thinnest edge (30°), CPM-440V (40°) was the thickest.

After that, I did some cardboard cutting (next week monday is paperday). Pretty much always cut agains the folds, and there was a lot of the same quality cardboard.

Judging from what I saw during sharpening, I kept cutting till the knife stopped clean cutting paper (I tested after each 5 cuts).

Altough the full flat grinds cut better from the start, after a while the geometry stops to matter, and the edgeholding of the steel starts to matter.

General order:
S30V => 40 cuts
CPM-440V => 45 cuts
CTS-XHP => 60 cuts
CTS-30BD => 65 cuts
M390 => 65 cuts
CPM-M4 => After 80 I stopped; it still cut paper cleanly, it just didn't feel sharp anymore.

Overall; very impressed with the CPM-M4 in the gayle bradley. To me; it begs for a thin edge, and it is by far the hardest steel in the test batch of high-end steels. It actually makes S30V look bad :)

Comments on red statements. I have the GB and Manix2 with M4. I get a beautiful, gorgeous mirror polish on the bevels. On the Manix2 I have a 24 degree inclusive back bevel with a 40 degree small edge bevel. The back bevel is pretty wide. I go outside and l can see a perfect reflection of the tree branches above my head without any magnification. The GB has a back bevel of 24 deg. inclusive and an edge bevel of 32 deg. inclusive. Same reflection level on it also. I will try to get pictures of the edges and post them in a few minutes. I don't know how good they will be. I only have a phone camera but I'll try.

The only steels I have experience with in your list is M4 and S30V. I love both steels. M4 is my favorite by far but S30V is my next favorite of the steels I have used. VG-10 and ZDP-189 are the other two I have enough experience with to have an opinion. They are both great IMO but I like S30V the best of those three. However, M4 is the best I've used. I would like to try the others but don't know if I will. If I do it will be quite a while. I'm putting buying on hold for a while. I now have a set of knives that combined have my favorite qualities. So, I'm not disagreeing with your statement about S30V being softer than M4. I was just compelled to put in a plug for S30V. I am amazed at how different people like one steel more than someone else. I guess it has to do mainly with the use and stuff we cut that may be different. But with the quality of the steels Spyderco uses they are all so good that it's hard to find one that is inferior. 8Cr13Mov and H1 have less edge retention but that is expected and both are still very acceptable.

Jack

[Alchemy1]

What are you using to sharpen Jack?

[jackknifeh]

What are you using to sharpen Jack?

I use an Edge Pro to get flat bevels. The finest grit stones that came with the EP are 600 and 1000 grit. They get a nice mirror finish but leave random very small scratches on the bevel. Then I use a fairly soft leather strop with DMT diamond paste (6 micron) to get a very very nice mirror finish. I still may have small random stratches the strop won't remove. I may also use the 1 micron strop I have. This does a really nice job.

I also have 3 Congress Tool moldmaster stones that fit on the EP, 320, 400 and 600 grit. These stones don't really get a great mirror finish but the scratch pattern is VERY consistant and VERY small scratches. They leave a nice finish that has a cloudy look. That's the best I know how to describe it. Then I get a nice mirror finish with the strops.

Finally, I have 2 Congress Tools Flex stones for the EP, 400 and 600 grits. I contacted Congress to ask about stones for the best polish results. They suggested the flex but that getting a mirror finish with just stones is rare. Usually you still need to use some sort of compound like diamond paste. I think most good stropping compounds will work but the paste I use is the only thing I've used. I only used the Flex stones once and that was just a couple days ago. They did leave the best mirror finish without stropping than any of the other stones. I still finished the edge up with the strops. The next time I use them I'm going to pay a lot of attention of the quality of mirror finish the stones leave before stropping.

When I use stropping for polishing I don't pay a lot of attention to the sharpness I get when finished. Just concerned about polish. After I have the finish I want I will touch the edge up with an UF ceramic stone. That creates a micro-bevel that's almost impossible to see but is razor sharp. I may or may not hit the edge on the strop with a few light strokes after the UF stone.

I hope this helps.

Jack

[Brock O Lee]

Hi Alucardje,

Thanks, interesting test...

I'm glad to hear that M4 performs so well, after you removed the surface decarburization.

I kept cutting till the knife stopped clean cutting paper (I tested after each 5 cuts)

What type paper did you cut to test sharpness? Phone book paper, or printer paper, or something else?

Can you maybe post the edge angles and grit finishes of the blades you tested with?

Thanks

[alucardje]

Well; I think I made something not clear. The polishing part was about the flats; the whole blade and not the edge. The edge is a straight mirror. An I try to avoid secondairy bevels, I usually sharpen on a loose trizact belt, which makes a gorgeous convex edge, and then I polish that.

I test on phone book paper; and like I said; I let the hardness of the blade and the feeling when sharpening guide me to the correct angle. I don't have an edge pro, but when I look at my spyderco 204; I usually end up inbetween the 30° and 40° angle. Only the M4 went below 30°, and that is the first steel to ever do that in my shop.

[jackknifeh]

Crappy pics of my edges.

This actually is the best picture. Look at the bevel and see the light bulb. It is one bulb in the light above the pool table. It is the thing that is in the best focus.
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[ATTACH]18241[/ATTACH]

[ATTACH]18242[/ATTACH]

[ATTACH]18243[/ATTACH]


Sorry about the quality. My phone camera doesn't do well very close.

Jack

[jackknifeh]

Well; I think I made something not clear. The polishing part was about the flats; the whole blade and not the edge. The edge is a straight mirror. An I try to avoid secondairy bevels, I usually sharpen on a loose trizact belt, which makes a gorgeous convex edge, and then I polish that.

I test on phone book paper; and like I said; I let the hardness of the blade and the feeling when sharpening guide me to the correct angle. I don't have an edge pro, but when I look at my spyderco 204; I usually end up inbetween the 30° and 40° angle. Only the M4 went below 30°, and that is the first steel to ever do that in my shop.

I did misunderstand. I thought you were talking about the edge bevel. So, just forget everything I said and definately forget the bad photos. I'm not even to the point of trying to polish the entire blade. It never has even occurred to me to try. I doubt if I have the tools and I know I don't have the experience.

Jack

[Brock O Lee]

Well; I think I made something not clear. The polishing part was about the flats; the whole blade and not the edge. The edge is a straight mirror. An I try to avoid secondairy bevels, I usually sharpen on a loose trizact belt, which makes a gorgeous convex edge, and then I polish that.

I test on phone book paper; and like I said; I let the hardness of the blade and the feeling when sharpening guide me to the correct angle. I don't have an edge pro, but when I look at my spyderco 204; I usually end up inbetween the 30° and 40° angle. Only the M4 went below 30°, and that is the first steel to ever do that in my shop.

Thanks Alucardje, that answers my questions...

I was surprised to see CTS-BD30 do so well in your test. IIRC it's supposed to be Carpenter's version of S30V. But here it outperformed S30V by a large margin. Could it be because of different edge angles?

It would also be interesting to see how Benchmade's M390 compares to Spyderco's M390, with the different heat treats. I have read that BM doesn't run it as hard as Spyderco.

Nevertheless, interesting test... :)

PS: Some pretty amazing photos Jack... :D

[JNewell]

Interesting note/result. I have seen a lot of knives where this seems to be an issue over the years, from just about every maker.

Hi Alucardje,

Thanks, interesting test...

I'm glad to hear that M4 performs so well, after you removed the surface decarburization.



What type paper did you cut to test sharpness? Phone book paper, or printer paper, or something else?

Can you maybe post the edge angles and grit finishes of the blades you tested with?

Thanks

[Rwb1500]

PS: Some pretty amazing photos Jack... :D

Bahahahaha!

That's cold blooded. :D

Hey, if Doc can change, anyone can.

[alucardje]

Interesting note/result. I have seen a lot of knives where this seems to be an issue over the years, from just about every maker.

Decarburization is simply the exposed steel getting too hot and having too much carbon and loosing carbon to the surrounding air and scale. When hardening stuff; I've always wondered what that black surface layer was ... always seemed like carbon to me.

Which is good on the sides; less carbon means less prone to rust. And bad on the edge where less carbon means softer cutting edge and less performance.

And why people should be more aware about this is simple. Technology. grinding and knife shaping has impoved to such a degree that almost finished products go in the hardening oven with much higher carbon percentages than in the old days. Steps are taken to prevent carbon loss; but none are any good except molten salt hardening and even that manages to loose carbon on the surface.

Point is that knifemaking has evolved to be much more precise before hardening and much less material is removed after hardening (because it *SUCKS* grinding a hard blade). Both result in a higher chance of decarburization reaching the customer.
And a knife that underperforms was not that bad; sharpen it a few times and be done with it.
Nowdays; a knife that underperforms is a pissed off guy making forum posts and youtube video's and this is a disaster.

like the S35V discussions on several forums...

[Brock O Lee]

Bahahahaha!

That's cold blooded. :D

Hey, if Doc can change, anyone can.

Hehe :o , sorry Jack I just couldn't resist... :)

[JNewell]

I could be completely wrong, but I've assumed that one possible, even likely suspect, here is a little to much heat at the very thin edge during sharpening. It's easy to do this, at least for amatuers like me. :o :)

Decarburization is simply the exposed steel getting too hot and having too much carbon and loosing carbon to the surrounding air and scale. When hardening stuff; I've always wondered what that black surface layer was ... always seemed like carbon to me.

Which is good on the sides; less carbon means less prone to rust. And bad on the edge where less carbon means softer cutting edge and less performance.

And why people should be more aware about this is simple. Technology. grinding and knife shaping has impoved to such a degree that almost finished products go in the hardening oven with much higher carbon percentages than in the old days. Steps are taken to prevent carbon loss; but none are any good except molten salt hardening and even that manages to loose carbon on the surface.

Point is that knifemaking has evolved to be much more precise before hardening and much less material is removed after hardening (because it *SUCKS* grinding a hard blade). Both result in a higher chance of decarburization reaching the customer.
And a knife that underperforms was not that bad; sharpen it a few times and be done with it.
Nowdays; a knife that underperforms is a pissed off guy making forum posts and youtube video's and this is a disaster.

like the S35V discussions on several forums...

[Blerv]

Interesting test and much appreciated.

The main thing that M4 suffers from that I've seen is assumptions. People are looking at the date codes and assuming machining leads to poor edges until reprofiled (and so-on). In fact, the last part seems the norm that once an edge is properly sharpened it does better than the factory settings. Not surprising since they use power tools instead of zen-like ceramic strokes.

I don't believe in wearing rose-colored glasses but until an overwhelming amount of detailed test data is presented it's often to let the internet be...the internet.

Listen, buy, test, come to your own conclusions. Unlike some things like college your initial investment is very little time and give/take $100 (which can mostly be recouped).

[Cliff Stamp]

... I felt it a liiiitle bit, but I couldn't see a bur. On softer conventional steels, I would have made a huge bur. Now is this steel really harder or is there something else going on?

A burr is just weakened and deformed steel which bent instead of being cut, or fractured instead of being cut. When a steel is fairly hard with a low to moderate carbide volume and small carbide aggregate then it tends to not burr at all unless over pressured.

I found S30V along with XHP to be the "softest" steels; CQ raising the biggest burs.

That is a fairly amusing statistic which shows just how extreme some cutlery steels can get when S30V is judged to have high grindability, you obviously have quite a nice collection of high alloy steels. How do you classify something like 420HC in comparison?

Really nice details, really nice.

[alucardje]

That is a fairly amusing statistic which shows just how extreme some cutlery steels can get when S30V is judged to have high grindability, you obviously have quite a nice collection of high alloy steels. How do you classify something like 420HC in comparison?

Really nice details, really nice.

Glad you like it. Cliff; I've been reading your reviews for over 10 years. Judging from the URL; are you a fysics professor or teacher (always wondered)???

Anyway, I have nothing in 420HC, but I have some AUS-6 (old endura in stainless and some 440C from böker. And I also tested some 52100 and 0-1 for comparison. Same belt; Trizact A6 belt. The 0-1 gave the biggest bur; then AUS-6, then 440-C, and 52100 which I hardened really hard to "emulate" CPM-M-4; made a really small bur too.

I think that hardness X geometry is the most important factor in the size of bur forming; and some side-effects of the carbide content and carbide size.

For clarity and future readers: I DON'T sharpen knives on a grinder. I form cutting edges on a grinder because the knives people bring me to sharpen are way too damaged to sharpen with a spyderco 204, and this became a habit. When a cutting edge is too far gone to be touched up on a 204, it goes to the grinder.

I only use the grinder this much for tests like this.

[Cliff Stamp]

The 0-1 gave the biggest bur; then AUS-6, then 440-C, and 52100 which I hardened really hard to "emulate" CPM-M-4; made a really small bur too.

Interesting on O1, if I had to guess I would say that is hardened in the embrittlement region which is what is causing that. I have one which was tempered at peak strength and it won't burr at all unless I over stress the blade and don't destress the edge before sharpening.

I think that hardness X geometry is the most important factor in the size of bur forming; and some side-effects of the carbide content and carbide size.

Yes, you need to match the hardness to the grindability. If for example you harden 440A at 60/61 HRC it will respond very differently than when it is hardened to the typical 55 HRC at which point it is like trying to sharpen dough. It also depends on your abrasive, the larger the difference between the abrasive hardness and steel (matrix and carbide) the smaller the burr, and as well as belts wear they form larger burrs.

Nice to see detailed discussion on sharpening which is rare, but critical as without proper sharpening the edge retention of any steel is skuttled. A proper honed 420J2 blade will easily have better edge retention than N690 which is not honed to quite the same level. That loss of initial sharpness carries over into edge retention dramatically.



That shows a Pacific Salt sharpened on one of those pull through carbide jobs. The green triangles shows the first run, the blade would easily slice newsprint but I could tell was not 100% crisp. The red line shows the average of a bunch of runs after I figured out how to get a crisp edge on the knife with that sharpener. The edge retention was 15 times as high. And again, but any common test of sharpness that first run was sharp, but if you measure it you would find it isn't optimal.


I have a PhD in Physics (Atomic and Molecular) and was at one point active in research/teaching, I am now in private industry.

[Zenith]

Interesting discussion. I have a GB on order now. I have a Military in M4 and have been very pleased.

As for the burr, I find it very interesting since no matter the steel I have sharpened, S30V, M4, RWL-34, D2, 440C, N690, 12C27 I have always raised a feelable burr. I sharpen with a Buck 3 stone setup, or in the field with a lansky 600grit diamond paddle.

I however seem to raise the burr on the coursest stone first, also the biggest burr when reprofiling, remove burr and after that it is easy to polish the new edge and remove the final burr with a strop.

In the field I only create a burr if the edge is really giving me problems or have a few nicks in and I want a new fresh edge.

[razorsharp]

bd30 beating s30v by that much...um...theyre the same steel, different company..... Ill just be honest, i dont follow those results

EDIT: was talking to donut, he said it was like XHP in his uses....DANG I wish i bought that manix now :o