sharpening heavy use large blades

[Cliff Stamp]

By heavy use I mean hours of chopping, so thousands of chops on thick brush and woods. I recently sharpened my old style Battle Mistress which had been used extensively clearing some land and limbing some felled wood. The edge could still slice newsprint but had no push cutting ability on the paper and there were some issues with cutting light vegetation. With the edge formed with a large 800 grit waterstone, the burr was easily visibly by eye and very ragged. This is a sign of a heavily fatigued edge which is common on large chopping knives which are heavily used. You can't remove this cleanly by alternating sides, it tends to crack and tear away the edge.

The knife was given one light stroke into the edge with a 1000 grit waterstone to grind down the weakened metal. The edge was reformed with the 800 grit waterstone and there was no visible burr and just a light one about 0.1 mm wide under magnification. Another pass with the 1000 grit waterstone was used and then the honing with the 800 repeated and the edge formed clean. The polish was then refined on a very fine natural chinese waterstone. This heavy initial burr formation can be prevented in many cases by sharpening more frequently to prevent the fatigue, usually only fine stones are needed unless the edge gets damaged from inclusions. The same general method works well to obtain a very high sharpness edge on heavily used machetes and such.

-Cliff

 

[Mtn Hawk]

Cliff--

What are the relief grind and microbevel angles on your heavily used chopping knives?

 

[Cliff Stamp]

On a decent steel I have found it difficult to go lower than about 12 degrees at the very edge and lower than 0.015" in thickness or less than about 8 for the relief. At that profile wood working is also limited to thick diameters, you would not want to try to clip off hardwood stubs for example. For general wood work which includes such limbing I move up to about a 8-10 relief with a final edge of about 0.015-0.020" thick at about 14 degrees per side. This is the edge on my Battle Mistress, Ratweiler, etc. .

On machetes and such softer blades you need a thicker geometry as the steel is much weaker. Now if I want the ability to chisel cut thick knots (inch or so thick) when batoning, I would make sure the final edge was about 0.025" thick or else it can actually turn through that thickness. It of course depends on the wood, if you are just cutting very soft woods like clear pine then you can go thinner. These profiles work fine on seasoned spruce, birch, oak, etc. .

It also depends on your skill and raw strength. I'll add for example about < 0.010" and 1-2 degrees per side for my brother who is the raw defination of brute force and ignorance when it comes to knife work. He is a carpenter who favors very heavy hammers and thus large knives like the Battle Mistress are pretty much weightless to him and he solves cutting problems by force over precision as he has lots of one and little of the other.

I would personally be curious as to what is necessary on the dense iron woods however nothing similar grows locally.

-Cliff

 

[TheButcher]

Cliff, I was wondering about your thoughts on the asymmetric convex edge on the older Battle Mistress'. I am about to order a new Fusion BM, and have an old Ergo model. I was contemplating getting the new one with the asymmetric convex edge, as I assumed for heavy chopping and all around field use that the asym. conv. edge would last longer, be easier to sharpen, and maintain itself better over the years. I like the old asym conv. edge on my old Ergo BM, but was wondering whether or not to get it on the new FBM and which edge actually would hold up longer, be easiest to field sharpen. When I got the old Ergo BM, I remember reading about the asym conv. edge and how tough it was in the field. thanks

 

[Cliff Stamp]

The performance of the asymmetric edge was mainly due to use of a relief grind, introduced by Busse in a very novel manner. As the blade is thickening as you move back from the edge and the force is decreasing you generally don't need to keep the edge the same angle. This is why the edge can be at 20 degrees but the primary grind at five. The addition of a relief bevel basically continutes this process. In short, yes, it is usually a good idea to use relief bevels in whatever form they are applied, convex or flat.

-Cliff

 

[TheButcher]

Ok, so does that mean Jerry had a winner for the old asymm. conv. edge and if so, I wonder why he changed back to symm. edges. Do you think it was because nobody really understood the asymm. edge concept or do you think it came down to better performance with the symm. edge. I had thought he changed back to symm. edges based on feedback from customers, in which, I figured they all liked the symm. edge more for looks only and not performance but maybe the symm. edge is better and just as easy to maintain in the field. Cliff, I really just want to know why you prefer a symm. edge on your old Bm vs. the asym. conv. that it came with. Is it easier for you to maintain in the field or does it really give a better performance while chopping. Or is it a trade off, asymm. conv.- tougher for chopping in the field, easy to maintain but not as cutting sharp as symm. and for symm.- not quite as tough for chopping in the field, not as easy to maintain, but can get very sharp for cutting. Thanks again Cliff for you insight, I'm just on the fence on which edge to go with, as I've become fond of the asymm. conv. for heavy chopping with my old Ergo BM, but just want to know which edge will hold up the longest in the field without much maintenance and freehand sharpening on a rod or sandpaper in the field. Thanks again Cliff, as I respect your opinions on the subject.

 

[D_R_Sharpening]

Cliff,
That must've been a hell of a lot of work to fix the edge on that knife with a 800x stone. I admire your efforts.

BTW - The fine Chinese waterstone that you used, is that the same one that people call "the doorstop"?


--Dave--

 

[Cliff Stamp]

...a lot of work to fix the edge on that knife with a 800x stone.

Sharpening was fairly minimal as the knife was not overly blunt, forming the burr was only 1-2 minutes per side. On most non-chopping knives I rarely have to use anything but the the finishing grit as they are usually kept very sharp, this is usually 600 or 1200 DMT or a fine natural waterstone or suitable ceramic. If they are visibly damaged I'll use a more aggressive abrasive, file, 200 silicon carbide or 80 grit belt on a 1" sander.

The fine Chinese waterstone that you used, is that the same one that people call "the doorstop"?

It is very small, about the size of a cracker. I asked a friend what they use in malayasia and he brought back a large coarse/fine stone similar to what you buy in hardware stores for $2 and the very fine waterstone. The waterstone is used for blades to cut fruits they harvest for oil and the larger stone on parangs. They don't use the full stones, they just hit them off a rock and share out the pieces.

I really just want to know why you prefer a symm. edge on your old Bm vs. the asym. conv. that it came with.

The main advantage of the asymmetric grind is that it provides the advantage of a relief grind while still allowing sharpening just one flat bevel which most people find easier to maintain. If however you are willing to use a relief grind on both sides of the edge this is a better option. This however does make sharpening a little more complex.

-Cliff

 

[thombrogan]

The same technique works well with most any knife when stropping stops working. Just did it tonight to restore a hair-whittling edge to my CalyIII.

Thanks for the advice, Cliff!

Somewhere online (or in my mind), I think you attributed this tip to Ed Fowler. Is that correct or am I spacing it again?

 

[Cliff Stamp]

A lot of people will recommend sharpening frequently but it is usually argued to simply reduce the time required. The way I sharpen large knives now is based on the method Fikes illustrates in his video with the modification that I don't go completely parallel but on a skew.

-Cliff

 

[sodak]

Cliff,
Now I'm confused. When you are talking about the relief grind, are you talking about the convex side of the Busse?

I took my Steelheart E, found the angle of the flat side with my Edgepro, flipped it over, and ground the convex side down flat at the same angle. It's not centered, but I'll have that fixed after a few sharpenings. The way that I'm going, and as long as this knife is lasting, it might be my great-grandkids who finally get the bevel even. Anyway, I polished it up to the 3000 tape, and I find this edge lasts a long time. By my rough calculations, this puts it at about 23 deg, or between the yellow and blue marks on the Edgepro. That's pretty thick, the only reason I haven't ground it thinner is sloth on my part.

Having said all that, I chopped down a tree last year, about 25 - 30 ft, then used a BM E to do most of the limbing and bucking. After a couple of hours of chopping, it took about 2 minutes on a ceramic stick to return to factory hair screaming sharpness. This is with the factory asymmetrical edge. I plan on testing the SH E against the BM E to see which edge lasts longer.

 

[Cliff Stamp]

When you are talking about the relief grind, are you talking about the convex side of the Busse?

On mine the convex edge was much higher and more acute than the flat.

By my rough calculations, this puts it at about 23 deg, or between the yellow and blue marks on the Edgepro. That's pretty thick, the only reason I haven't ground it thinner is sloth on my part.

Yeah, mine was about 35 included.

After a couple of hours of chopping, it took about 2 minutes on a ceramic stick to return to factory hair screaming sharpness.

Yeah, it works well for that type of work, high impact steel so there is no chipping, fairly hard so it resists wear well and enough chromium and carbide to give decent corrosion and wear resistance.

-Cliff

 

[thombrogan]

Not the frequent sharpening. The slicing into a hone at a 90 degree angle to deburr fatigued steel. I also see that Dwade recommends it, too. Infinitely better than whom advocates what is that it works great.

 

[Cliff Stamp]

I don't recall hearing that from Fowler, it is a natural extension of Clark's high angle burr removal. Quite a few years back Chad Engelhardt mentioned that when sharpening large machetes and similar blades he preferred to not align the deformations extensively before sharpening because that just pushed weakened metal on the edge and thus just sharpened the edge completely fresh. That got me thinking about edge condition when sharpening which solved a lot of problems.

-Cliff