Regrinding Blades

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me2

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Oct 11, 2003
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Just to see what would happen, I took my grandmothers old machete and reground the edge. Essentially, I took a normal GI type machete and added a primary and secondary bevel. The primary bevel is 5/16" wide, on 1/16 thick stock, so it's somewhere between 3 and 4 degrees. Then I added a secondary bevel at 19-20 degrees. The secondary bevel is a little less than 3/64" wide, and 0.025" thick at the top of the bevel. After sharpening, I proceded to chop a 4x4 in two, and the blade would still shave my arm, in the area of impact.

The thing that bothers me about the whole regrinding session is that the edge on a large chopping knife is thinner than the edge on my Delica by about half (0.047" vs. 0.025") and it does it's job with no damage. My Delica is a couple of years old and has seen some heavy use. It has been sharpened many times. The question becomes though, how thin could I go on a pocket knife before I start seeing damage? I do all sorts of stuff with the Delica, from cutting wire, scraping rust off pipes, trimming threads, kitchen use, whittling, cardboard cutting, etc. Looks like this weekend I'll be regrinding the Delica. Hopefully, I'll be able to finish regrinding my Kudu as well. It took some damage and was being reground from that. Might as well thin it out while I'm at it. As long as I'm wishing/guessing, I might as well shoot for as thin as I can manage, say 0.010" or less with 15 degree bevels.
 
15 Degree bevels is awe full high IMO. What I do it regrind the blade to a zero edge then put a micro bevel about 7-10 degrees per side. Holds up just fine from my experience.
 
The possible edge angle before rolling and chipping is solely dictated by the blade itself, i.e. the steel and the heat treat/cryo etc. That should be the reason why people buy expensive steels, yet it isn't, because most people leave the edge angle at 20° per side — when you could go half of that on super steels!
 
Even for non-super steels, you could go half that. It just reduces the variety of things you can do with it. We'll see how this weekends grinding efforts turn out.
 
Yeah absolutely. I just regrinded (zero convex) my Izula too far, so the edge rolled all the time when cutting wood. I gave it a slightly less acute edge and now it is the sharpes thing I own (1095 steel) and it holds it's edge perfectly. It's all about getting to the level were it doesn't roll anymore. That's how far you can go and super steels tend to do this better than average steels. At least that's why I even consider such expensive blades. Otherwise I can just use a plain ol' Mora to get the job done.
 
I'll be interested in your results! One of my best was a Spyderco Calypso Jr. in ZDP 189 that Tom Krein took down to less than 0.010 (I want to say 0.005, but gave it away). It held up much better than I thought it would, until I did something really stupid with it. My fault.

Once you get it that thin, the edge bevel becomes a micro bevel! :D
 
If the Delica is VG-10, I'd bet the biggest issue might be with a wire edge that will roll, if subjected to hard use. Especially so at thinner edge angles. Without exception, every VG-10 blade I've re-bevelled to a more acute angle has always presented a very stubborn wire edge after the fact, which takes some time to remove. The wire edge will persistently hang on, and 'flip' side-to-side or roll over completely, effectively rounding or dulling the edge. This steel is very ductile, which becomes more apparent at thinner edge angles.
 
I don't really have a reason to go as thin as 10 degrees per side or less. For the occasional scraping session, or cutting week whacker cord, I'd want the main bevel to stay at 15 degrees or higher. I just want to be able to resharpen it faster. Like I said, I've used this knife for over 2 years at work and it has lost maybe 1/16" of width from resharpening. The edge has thickened a lot and takes forever to resharpen. I have my dad's old trapper from Parker Cutlery. I keep one blade at 12 degrees per side and add a 15 degree Sharpmaker microbevel. It will roll, but only when I use it for whittling and have to lever out wood from between forks or something (whittling slingshots).
 
This weekend I finished up regrinding the Cold Steel Barong machete, from the infamous "utility" edge to an actual primary/secondary bevel configuration. Its again 3-4 degrees per side, as on the last machete regrind. Bevel height is roughly 1/2" wide, but it is pretty wavy. I left it at a worn 40 grit finish. These belts are the suck. It took 4 belts to do this on a 1x30 sander, at 40 grit. I'm going to try some different ones for the Panga. I may polish it more one day, but it's fine for it's intended use.

The actual edge bevel is at roughly 20 degrees, put on with a slack, very worn, 180 grit belt and stropped off with the leather sander belt. I measured it with calipers and the thickness behind the edge is 0.015". The calipers set at 0.02" will slide up the blade beyond the secondary bevel.

To test it in it's new configuration, I found a branch about 4" in diameter cut from the tree in the back yard. It's dry and has been lying in the brush pile for a few weeks. It was already limbed, and didn't have many to start with. I bucked it into several pieces and checked the edge afterward. It will still shave hair in the section used to cut the branch. It would also still cut grass blades and other light plants. Checking the edge I found a few places with some damage. However, I cannot say these came from the chopping. This blade was used before quite a bit, and had some damage in various places left from that. I know there was a region near the tip with damage that is still present, surviving the resharpening and regrinding.

The damage is not visible, and doesn't even reflect light, but can be felt when running the edge along my fingernail. The old, known damage near the tip survived because I started at 10 degrees and walked the new primary bevel up the blade, without actually removing the old 20 degree bevel. The resharpening was done on the 180 grit belt and leather and raised a burr that was removed by the leather. The burr was minimal, barely visible, and I have my sander set up horizontally so I can see a burr as it forms from a light over my shoulder. The bucked branch was kinda dirty, and if the damage at the sweet spot is new, it likely came from that.

During chopping, which was done kneeling beside the branch, I found I could bury the blade into the branch to the top of the new bevel. I could do this before, but the bevel was only 3/16" wide. There were some binding issues when the blade would bite this deep. Oddly, this seemed to be hand dependent. I had almost no binding with my right hand, and nearly all of it happened when chopping with my left. I'm left handed, FWIW.

In summary, this thing works great now. It made several cuts through the branch and would still shave my arm and had no visible damage. The thin edge didn't take any damage, and I went through the knottiest part of that branch, though to be honest it was pretty clean besides that one spot. The sweet spot is almost dead center of the blade, and this took some getting used to after using the Panga and Kuhkuri models for so long. The Barong is my newest model, and I've been using Panga patterns since I was 12 (I'm 36 now). I have some more cleaning/breakdown to do in the back, and I'll likely use this one to see what happens, unless I get some new belts and some time to do the Panga.

I really need to finish the Kudu and then regrind my Delica. These would both be cutting wonders at 0.005" behind the edge, which should be no problem given what the Barong did today. I'd still leave the angle at 15 degrees, but it would be so narrow, it would take no time to lower it if needed.
 
stoffi said:
The possible edge angle before rolling and chipping is solely dictated by the blade itself, i.e. the steel and the heat treat/cryo etc. That should be the reason why people buy expensive steels, yet it isn't, because most people leave the edge angle at 20° per side — when you could go half of that on super steels!
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True enough, though I have to ask if you've ever seen how wide that edge bevel gets at 10 degrees per side? If the original grind wasn't a zero edge FFG or convex to begin with, the thickness behind the edge would leave you with a bevel that takes up 1/4 of the blade itself. I feel I'm pushing it hard enough on my R.J. Martin Overkill at 15 degrees per side, even with the hollow grind. Would be the fugliest thing I've ever seen to have as much mirror polished edge as I do stonewashed blade:thumbdn:.

For some super steels I feel I get enough of an advantage with the increased wear resistance and near corrosion proof blade.
 
There are a lot of variables that go into this sort of thing. The heat treat is going to be very critical - most machetes are quite a bit softer than their small knife brethren. I have personally sharpened up a CS bolo and made about 6-8 passes through a down and seasoned length of American beech 3-4" thick and had it still shave (with a tug) some armhair. Considering this wood is harder than red oak, I'm confident it could easily hold a wicked edge after several passes through pine. This was a convex edge at approx 28 degrees apex. I don't believe it could hold up as well to a lot of draw cutting - it just doesn't have the type of wear resistance that would be needed. I do have a Condor mini bushlore that I'm EDUing and intended to compare (informally) the relative wear resistance between a Imacasa machete using 1075 and a small knife using the same steel at the same approximate angle. Personally, I believe if you use a chopper careful to direct it into the cut as perpendicular as possible, the edge will last a long time even with low carbon steel and a mild heat treat. Still, the trade-off has to show up somewhere - even a relatively fine toothy edge, say 1000-1200 grit, will wear away faster than if done on a harder steel with a wider apex.
 
I think I've said it earlier in the thread, but my intent was to just reduce sharpening time by adding a huge relief bevel. But it works so well, I want to try my panga and kukuri models. I have no idea how hard the steel is. For chopping I use a polished bevel (this one was power stropped). Were I cutting blackberry, tall grass, or rose bushes, I'd maybe use a coarser finish, if I knew ahead of time. There's a fine balance between hardness and edge holding, and the ability to repair damage easily. If you have a belt sander, you can get away with some different steel than if you have to do everything by hand and use files or a stone. That was the reason for this. I can resharpen in minutes with stones or easily remove damage with a few file passes. I may do the panga at half the angle of the other two, just to see if it will hold it. Maybe also go to a 15 degree bevel. I'll have to content myself with thrashing the Barong and unknown granny machete until I get some more coarse belts.
 
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me2 said:
... I'll have to content myself with thrashing the Barong and unknown granny machete until I get some more coarse belts.
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I just remembered you said this. Am in the process (off and on) of setting up a Tramontina 14" bolo for camping next year. The factory grind is (was) extremely perfunctory. After having a go with a piece of 80 grit sanding belt I decided to wise up and use a file. I keep forgetting its a better option on the softer steel used in machetes. Picked up a new 12" single cut Nicholson and the thing can do any bevel resetting you'd care to try in very short order. Very worth the $ if you're planning on doing a few of these things - no point in trashing your belts.
 
I tried a file to start with, but it didn't really do much but scratch up the bevel. Perhaps a new one is in order. The belts I was using are really cheap, and taking the barong from 10 degrees per side to 4 degrees per side uses a 40 grit belt up. I'm hoping not all of them are like that.
 
A new single cut Nicholson (what they had at HD) is doing a fast and clean job on my Tram - believe its 1070 steel. A new file should make quick work of the 1055 used on the CS machetes.
 
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