edge bevels, sharpness and S30V

spyken

spyken

Joined
Apr 29, 2002
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I'm in the process of getting a 4 inch custom tactical fixed blade by a known knifemaker (shall not mention names), with S30V steel. I am told that the maker's usual edge was 42 degrees (inclusive). Having read many posts espousing (1) the benefits of going for a more acute edge bevel to get a sharper edge; and (2) S30v's toughness, I asked for a thinner 30 degree (inclusive) edge.

I was therefore surprised when the maker said that he could do a 30 degree (inclusive) edge, but that that edge MAY be more prone to chipping as CPM steels demonstrated a possible chipping-propensity (presumably at such acute edge bevels).

I am of course no expert on such things (I really just wanted a SCARY SHARP edge) but am surprised.

Is 30 degrees (inclusive) too acute for S30V?

Is S30V prone to chipping at such angles?

Isn't S30V tougher?

Does heat treat matter? (I didn't ask who carried out the heat treat or what the rockwell is - I assumed that the maker would be the expert)

Can you guys share what you think? I don't want a brittle edge, but I thought that you guys almost always recommend that one should go for a edge that is 30degree (inclusive) or less, ESPECIALLY WITH S30V'S TOUGHNESS.

What is the usual recommended edge angle (inclusive) for a custom knife?

I really like the maker's knife design, and I have no doubt that he is an expert in knifemaking, but am a little confused now.... :confused:

spyken
 
It's hard to give simple yes/no answers without having a lot of caveats. A lot depends on the HT, edge thickness, etc, and what you're cutting and how you use the knife. But, why not try it at 30 deg and if it doesn't hold up as well as you like, you can back it off a bit. Simple enough...
 
What the knifemaker said is true in the general sense and more true when you consider other factors.

Thinning the edge makes it more prone to chipping. This is true for any steel, any knifemaker, any heat treat. A blunt edge will take more abuse before failing.

If you don't control the heat treat properly, you increase the chances of getting a brittle blade. CPM steels are among some of the most difficult steels to heat treat properly. If you do "in house" heat treat, you may not be able to properly heat treat CPM steels. If you do good "in house" heat treats on these steels, you have a large investment in the tools to do it. Many major knifemakers send their blades off-site for heat treatment because of issues like this.

I have a Trace Rinaldi TUK knife in CPM S30V. I don't know what the edge geometery angle is to be honest. Trace knows more about that stuff then I do. What I do know, is that I have personally done full power cuts into solid Oak with all the force my small little arms could muster and the knife and blade showed no signs of stress.

Now, ask yourself what sort of use this knife will get. Are you going to pry with it? Are you going to do full power strikes into really solid objects (hardwoods, soup cans, etc.)? Are you going to slice free hanging tissue paper and shave arm hair? Do you intend to use it to do gentle cuts into your thumb to pick out wood splinters (no kidding - I have had really sharp working knives that would not do that safely because of the edge geometery)?

Know what you want to use the knife for, have it built for that task and, enjoy it. I do not use my Murray Carter Muteki kitchen knives (RC 62 and very thin and acute edges) to cut up chickens. On the flip side, I don't use my Wustoff/Henckels kitchen knives to dice onions and similar vegtables. Get the right tool for the job :D

-----

RJ's post and mine were going on at the same time. He brings up a good point. IF the blade suffered minor chipping or, just didn't hold up well at that angle, his suggestion to back it off a bit is a very good one :)
 
Thanks RJ and Sid.

The reason I suggested 30 inclusive (even though I'm no expert)is:

- I wanted to avoid having to reprofile (if necessary) a 40 inclusive down to a 30 on my sharpmaker. I don't have diamond stones presently;

- I've been reading the posts on edge bevels and finish grit posts by Cliff, Joe and many others on how they increase cutting performance;

- as I understand, Spyderco grinds their blades to 30 included, including S30V models. I believe that there's a good chance that customs would outperform productions ceteris paribus, yes?

(btw, I'd like to add that I do love my spydies n I think they're sharp)

- I like sharp!:)

would it be better for me to leave the edge bevel angles to the maker's judgement (given the usage parameters I provide), so long as it's below 40 degrees inclusive?

Thanks in advance.

Spyken
 
S30V with a high RC (59 and over) and a thin edge geometry has been known to chip. What is the knife going to be used for? Is the knife going to be very thin behind the edge as well?

The edge angle should be determined by what the knife will be used for. Since it is a short blade your knife will probably not see much if any chopping, so 30 degrees should be fine. If it is possible that the blade will hit bone or any other hard material during use you may want to have the maker back off on the heat treat a little and go for 57-58 RC. The edge will not stay sharp as long, but it will stand up better.

Like RJ mentioned, it would probably be a good idea to try the knife with a 30 degree angle and the regular heat treat and see what happens.
 
Based on your other posts and email, I think the 30 degree inclusive angle is appropriate. In my case, I use folding knives pretty hard. What do I consider hard? Cutting wire, not just thin copper wire but, electric fence wire. I pull industrial staples with them. Then there are those hard hoses, often with strenghting cords in addition to just being thick and tough. This type of use is very hard on knives and makes cutting bagels in half and opening mail seem truly trival in comparison. A knife for this type of abuse is a different creature from what I suspect you are looking for.

For food preparation, light yard work (stripping small branches and twigs), cutting paper stock (not industrial strength card board), fabric, etc. you want something much different then the tool described above.

If you are limiting yourself to even less stressful use, you might want go even thinner. Are you looking for a razor to cut hair and slice tissue paper? Edge geometery is important here too.

Define the boundaries of what you are going to cut and, we can help you even more.
 
Thanks Sid,
This one isn't the folder we were talking about ;) , but a tactical hollow ground 4 inch fixed blade I'm considering (together with others). It's probably going to be 5/32" thick.

Probable use:

(1) mostly outdoor utility cutting - cutting plastic /alum foil (MREs, ziplocs, ripstop nylon, elastic cords, fabric (nylon, cotton, cordura), nylon rope/webbing, manila hemp, climbing rope, tow ropes (kayak), skinning/cuttin meat/veggies for camp food prep, light camp craft (no chopping, maybe shaving wood for fire starting);

(2) some urban utility - cardboard, paper, packing tape, thread;

(3) SD (if necessary, conceptually at least) - stabbing, cutting through canvas/ballistic nylon.

I'd like it to be shaving sharp as well (is that too much to ask, bearing in mind the above?) - at least it should slice newspaper smoothly without snagging :D and shave hair too!

ps: sid, where's that obie framelock you were hinting at :p ?

spyken
 
Like the others have said, it depends, on what you want to use it for. S30V can chip just like any other steel, it's tough but not the toughest, it's stainless but not the most stainless. But it's the best stainless steel available. I have a 4 inch fixed blade at rc 61, I did put on a 10 degree per side 20 degrees included. Did I chip it? Yes but it took some hard use to do it. Cut through the bottom of a beer can and cut a large industrial staple. With this low angle and hardness the chipps were still fairly small and were sharpened out after 2 more sharpenings. I would think that a 30 degree edge should be just fine for most common uses. If you do find it chipping on you just give it a few strokes at a higher angle, that will be easier than trying to make it thinner from the 42 degrees.
 
Looks like you posted right before I did. 30 degrees should be just fine for what you listed.
I think S30 takes a killer sharp edge should work great for you.
 
oh, I would like to add the following things that the knife should cut through w/o the edge chipping or rolling:

aluminium cans, 10 litre olive oil/cooking oil cans, pepsi bottle plastic (to fashion camp tools etc), stab through 3/4" wood.

also, can any knife with a 30 inclusive edge cut through (1) chicken bones, (2) open can food lids without chipping?

thanks,
spyken
 
Originally posted by spyken
oh, I would like to add the following things that the knife should cut through w/o the edge chipping or rolling:

aluminium cans, 10 litre olive oil/cooking oil cans, pepsi bottle plastic (to fashion camp tools etc), stab through 3/4" wood.

also, can any knife with a 30 inclusive edge cut through (1) chicken bones, (2) open can food lids without chipping?

thanks,
spyken
Click to expand...

Sure, but there will always be a chance that you will chip the blade. You may cut through dozens of chicken leg bones with no problem and then the next time you do it the blade chips. Be careful when opening cans. When doing this you will be putting torque on the blade and it will be more prone to damage.

Stabbing through 3/4" wood will not be a problem as far as the edge is concerned, but be careful not to have too thin and pointy a tip.
 
spyken :

aluminium cans, 10 litre olive oil/cooking oil cans, pepsi bottle plastic (to fashion camp tools etc), stab through 3/4" wood.
Click to expand...

None of the above is even difficult for even a medium quality steel, and 15 degrees per side is overkill.

can any knife with a 30 inclusive edge cut through (1) chicken bones, (2) open can food lids without chipping?
Click to expand...

Mild steel blade, 12 degrees per side, 22 degree microbevel (beyond visible, less than 0.005" thick), easily cut chicken bones with no damage, not even excessive blunting :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=261961

Lots of other kitchen work, and various wood work including very hard baton work into seasoned wood. No edge problems. Again *unhardened mild steel*. No metals cut with it yet.

Deerhunters (with thinner bevels) used to cut through chicken and other bones and 3.5" nails :


http://www.bladeforums.com/forums/showthread.php?threadid=243045

I would go under 15 degrees per side with the knife unless you plan on attaching it to a pole and using it as bill hook as that extent of an obtuse bevel is only needed on a felling axe, or a knife used to cut thick hardened metals very quickly.

Get the bevel down to 10 degrees per side, and put a small microbevel on with the sharpmaker at 15 degrees per side. Most metals cut like wires and such, are not hardened, as long as you don't cut into them and then twist the knife, the blade should handle it fine. The best way to cut heavy wire is to chisel cut it with a baton.

-Cliff
 
Originally posted by Cliff Stamp
spyken :

None of the above is even difficult for even a medium quality steel, and 15 degrees per side is overkill.


Get the bevel down to 10 degrees per side, and put a small microbevel on with the sharpmaker at 15 degrees per side. Most metals cut like wires and such, are not hardened, as long as you don't cut into them and then twist the knife, the blade should handle it fine. The best way to cut heavy wire is to chisel cut it with a baton.

-Cliff
Click to expand...

:eek: :eek: :eek: :D
I was waiting for you to chime in, Cliff.

So far, I've had quite a few differing views on this - some makers have told me to stick to 20 degrees per side, and assured me that this could still produce a scary sharp edge. Others have told me to go for 15 degrees per side as they've said that S30V can take it, if heat-treated properly. Yet others have told me to leave all this to the maker to decide, and for me to stay out of it :p :) .

So the jury's still out....I personally would be happy if I could go for 15 degrees per side, and still do all the above cutting. My experience with a 20 degrees per side on my SOG seal pup was not very pleasant :( , I had to thin the edge down a bit to make it more efficient.

Hoping for more feedback here....
 
You can get the edge very sharp at any angle, however the cutting ability will be relatively very low at 20+ degrees. Regardless of what edge you need for durablity reasons, there is also no need to have the entire edge ground at that angle.

Chipping only happens to the edge on a small fraction of its width, only this width needs to be at the more obtuse angle. Anything other than this is an unnecessary waste of cutting ability and just makes sharpening more time consuming.

The exception to this of course is knives ground with really thin bevels, like 0.005" thick and under. On them you don't duel grind the edge because it is so narrow, the primary grind takes the place of the shoulder or relief grind on most blades.


My experience with a 20 degrees per side on my SOG seal pup was not very pleasant , I had to thin the edge down a bit to make it more efficient.
Click to expand...

This isn't influenced significantly by steel. Thus any steel ground at that geometry won't cut well.

As a lower bound, just grind down the SOG until the edge breaks apart and use that to set an upper limit on the S30V custom - it has to be more durable than the SOG.

-Cliff
 
cliff, can I send you an email off-line? I'd like your thoughts on some specifics privately (the particular knife etc) ....which is the best email to sent to?

thanks,
spyken
 
what is the usual edge thickness? how thin should the ideal edge be? is 0.022 thousandth of an inch (?) a good edge? can it take a 15degree per side edge angle and still be strong enough for my application?

or should I go 0.022 edge with 17 degree per side edge angle?

or 0.022 with 20 degree per side edge angle?

or 0.025-28 with 15 degree per side edge angle?

the above is on the basis that the edge is finished with a 150 grit belt for micro-serrations and thereafter buffed/stropped with a leather wheel.

I know it may seem that this is all theoretical, but since it's custom, I want to push the envelope in terms of cutting performance (but bearing in mind durability).

thanks,
 
The Deerhunters that I used to chisel throught the 3.5" nails, and seal and chicken bone were 0.015-0.020" thick, and from 12-15 degrees per side. This is a fairly durable edge profile and really only needed for similar fairly extreme tasks, most knives can go far smaller in edge profile without any problems.

The MEUK I had modified by Caffrey for example has an edge bevel at 0.005" thick, and has seen use for work up to and including splitting knotty wood. I don't think it would be up to cutting nails however. For soft materials like rope, foods, cardboard and whittling wood, you can go very thin, the Mel Sorg custom I have has a ~5 degree edge.

As a very large blade example, my older SH Battle Mistress (large bowie, blade heavy, 660 g), ground at 8-9 degrees per side would ripple on hard woods to a depth of 0.005 to 0.010" . With a very slight secondary edge bevel just a few degrees more, it handles such wood working fine.

Thick edges are generally only needed for heavy impacts into hard targets like rock, hardened metal or really dense bone. Chopping up a concrete block for example can dent an edge up to 0.020-0.030", depending on the power of the swing (fractures can be much deeper). Therefore you want the edge at least this thick to prevent damaging the primary grind.

The only reason you would need 0.020"+ thick on that small a knife would be if you were going to attach it to a stick and thus turn it into a much larger knife and hack away into something hard like a rock, or use something hard like a rock to pound on the back of it to cut through something hard like a large leg bone in a hurry.

That being said, steel properties do change depending on type and heat treatment. It is always possible that you do need 15 or even 20 degrees per side abd 0.020"+ thick for durability depending on the maker. The arguement then would be that maybe it is time to look elsewhere if the maker will not support the geometry that you want.

-Cliff
 
cliff,
thanks - got your email. appreciate your comments. I'm a little astonished about the differences among the various heat treats over the same steel.
 
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