Holy COW! Using the Sharpmaker BACKWARDS!!!

L

Lavan

Joined
Nov 8, 2000
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Esav posted in another thread about using the angles in the reverse order of that suggested by the Sharpmaker video.

AMAZING!!!

Worth a new thread! I got to thinking about that and decided it WOULD make sense. And it does! SHARP! YOWZIE!

Using the white stick EDGES and using the EDGE angle first. THEN the "Back" angle.

I figger it eliminates any of what just HAS to be SOME degree of variance in the supposedly vertical positioning of the blade. So...you're putting the ...final... edge on first. And using the steeper (supposedly first) angle LAST hones the SIDES off that edge without touching the actual edge that you just put on. And..... if there is some variance in verticality, you won't be doing anything more than honing an EDGE on a small irregularity. And, as he said, you are polishing the sides off to a degree and actually ending up with more of a convexity in the final result.

Ya'd hafta WORK at it to screw up the edge doing it this way.

I'm a convert now. Bassackward sharpening from now on.

:) :) :)
 
That sounds very smart.

I'm going to try it on my next sharpening - let's see, realistically it will be an 8" chef's knife in 420 -
 
So you mean start with the 30* slots and move up to the 40* slots? I'm going to try it on one of my SAKs.
 
moving-van.jpg
 
Django606 said:
So you mean start with the 30* slots and move up to the 40* slots? I'm going to try it on one of my SAKs.
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Or is it the other way around? I don't use 30* very often :p
 
It's called a "poor man's convex". Use 40 degrees to get a strong working edge. But this leaves you with a wide secondary bevel. So follow this with 30 degrees to reduce the angle where the primary and secondary bevels meet -- the "shoulder".

A convex edge curves smoothly down from the flats of the blade to the edge. A poor man's convex "curves" down in three steps instead of a smooth curve: the flat (the primary bevel), the shoulder, and the secondary bevel.

This reduces friction as the blade slices through material.
 
Lavan said:
Ya'd hafta WORK at it to screw up the edge doing it this way.
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Hardly, read for example Clark's extensive commentary on burr removal necessary on some steels and then think about the above method. Do you really want to work on the relief grind after you carefully honed the primary edge to a perfect finish. Not to mention that you can do the relief grind really sloppy, it doesn't need precision or accuracy, it is just a shaping process. I can relief grind a ZDP-189 folder from 15-20 degrees to 5 in less than two minutes on a 200 grit waterstone. I would not want to do that after I carefully honed the edge, not to mention the edge is much easier to hone after the relief grind has thinned it out.

Esav Benyamin said:
It's called a "poor man's convex".
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Multi-beveling and is done for a different reason than a convex grind usually. Specifically on tools you alter the angles with every finish to increase speed of sharpening, Lee notes this in detail. It isn't uncommon for chisels for example to have 2-4 bevels for those people who take them to very fine finishes. Convex bevels on the other hand are generally full honed with each grit and thus usually best left for easy to grind steels.

People like Juranitch popularized the use of multi-bevels and the term relief grind to enhance cutting ability and ease of sharpening, however this is a very old technique. You can see it for example in Cook's book on sharpening where he specifies the exact edge angles an axe bit should have from the mid blade hollow to the very edge and then the last v-ground micro-bevel which should be applied.

A convex edge curves smoothly down from the flats of the blade to the edge. A poor man's convex "curves" down in three steps instead of a smooth curve: the flat (the primary bevel), the shoulder, and the secondary bevel.

This reduces friction as the blade slices through material.
Click to expand...

Reducing friction isn't the significant effect seen when you change edge profiles and isn't the main reason you use convex grinds. You are critically reducing the wedging forces against the sides of the blade. The actual frictional forces are usually trivial unless you are cutting very sticky material like cheese. This has actually been measured, Lee notes this in detail on woods.

There is a reduction in friction when the polish is raised but this is generally very minor compared to the wedging forces. Note for example Joe's Axis post where he left the knife with a rougher finish and the cutting ability increased hundreds of percent due to the reduction in wedging and increase of slicing aggression.

-Cliff
 
Is the above picture accurate? So say I just sharpened my BM Ares at 20* (which I did), and I removed the burr, etc., I could do this and remove the shoulders, which would make the knife even sharper and cut better? Could someone explain this a little more? Also, which stones/sides do I use? After you use the knife until it needs another sharpening, which angle would you sharpen it at?
 
Lavan, you are not a machine and it only takes *one* miss stroke to completely undo all the efforts at honing the primary edge. Yes it can be done if you are careful but it has no advantages to do it in reverse order and is actually extremely inefficient because you are forcing precision where it isn't required and missing out on the ease of sharpening of honing the relief grind first.

Django606 said:
Is the above picture accurate?
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It is an approximation, it assumes a machine used the sharpmaker and the angles are exact. In reality it isn't. All edges will be convex due to human variance on the stone. Even if you use a jig most stones will wear and induce curvature, waterstones do this immediately on the lower grits for example and can induce a curvature of 2-4 degrees *per side* during one sharpening session.

say I just sharpened my BM Ares at 20* (which I did), and I removed the burr, etc., I could do this and remove the shoulders, which would make the knife even sharper and cut better?
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Yes, however it would make more sense to cut the relief grind first with a coarse stone which reduces the amount of work it takes to apply the secondary grind. This increase in ease of sharpening is in fact one of the main reasons you use a relief grind in the first place.

Also, which stones/sides do I use?
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The relief grind doesn't need to be precise or accurate, ideally you just cut it freehand with a x-coarse hone. I use a 200 grit silicon carbide waterstone. It will reprofile any steel I have seen, and I have used some of the hardest and most wear resistant alloys used, from 20 to 5 degrees in a couple of minutes on a small folder. The steel is literally ripped off similar to how a file cuts into a machete, or a wood rasp eats through pine.

After you use the knife until it needs another sharpening, which angle would you sharpen it at?
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The final edge angle until it thickens to the point you notice it taking longer to sharpen or the cutting ability is reduced and then you recut the primary. Generally this takes a long time as in a year or so. You can prevent it completely by just working the primary periodically whenever you have the time.

-Cliff
 
My Ares is fairly new, and I have only sharpened it a little bit. In the other thread where I was having burr trouble, you said that it would make life a lot easier on me if I ground a relief grind. Can this be done on the Sharpmaker? Is this what the 30* setting is?
 
That is what it is intended to be yes. The video recommends sharpening at 20 and setting the relief at 15. However many Spyderco knives actually come at 15 degrees or under and in general for most use, outside of really heavy work like cutting metals and such, you are better off with a more acute relief grind. I run relief grinds of 10 degrees on heavy use knives (chopper/splitters) and 5 on the utility ones. Jeff Clark has described how to do 10 degree grinds on the Sharpmaker, but in general I would recommend just using an x-coarse hone freehand and keep the Sharpmaker for the final edge bevel. Relief grinds are just shaping, you don't need precision or accuracy.

-Cliff
 
So you're saying it is better to grind the relief angle BEFORE I sharpen at 40*, right?


..which is the opposite of what Lavan is saying. I think I'm starting to understand this now, thanks for bearing with me guys :o

As long as I am happy with my current edge, there is no problem with grinding the relief angle afterwards, right?
 
Cliff, what do you think I am doing that makes the edge come out better (for me) by doing the 40 degree first?

I am assuming that I am not consistent on the final grind (after the recommended relief grind) and by doing it this backwards way, I am compensating for sloppiness by possibly ADDING a small portion of the edge at a steeper angle but only where the edge was uneven to begin with.

???????
 
I don't really see how it could possibly make a difference if you are working it really the way you show it. Whether you are applying the backbevel in the beginning or at the end. If you don't hit the edge you don't hit the edge.

If I understand you correctly, you are using the grays for the backbevel? My guess is that you are actually hitting the edge occasionally and lightly with the grays while working the backbevel, giving the edge more aggression. Some people, Vampyrwolf among them like to run, after the final polish, the edge lightly just for a couple of strokes over a coarser grit to give it some teeth. Just a guess though.
 
The toothier edge will still push cut and slice, right? How long do you use the gray stones after putting the final edge on it? I'm assuming you alternate sides every stroke, right?
 
Well, personally I am not too fond of doing it. I have played around with it, but my personal preference lie with very polished edges but this is a personal preference. But if you give it a bit more tooth, you want to use just a very few passes at very light pressures. You don't want to completely rough up the edge again, you simply what to "divide" the polished edge into "teeth". And yes, alternating. The last thing you would want to do is build accidentally a burr. And yes that edge will push cut and slice. I will not push cut as well as when leaving it completely polished but you definitely gain slicing ability.

It is a very old technique. Before bread knives were serrated they were sharpened in the traditional way (benchstone) and then the edge was divided into teeth by going over the edge with a special, very coarse file perpendicular to the edge.
 
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