Belt Sander VS Edge Temper

Jerry Hossom said:
As for removing too much steel, a 15 micron belt doesn't remove nearly as much steel as some of the more aggressive DMT stones.
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Yes, I think you need to separate people on the forums sharpening high end knives and the everyday guy who gives you a knife when you mention that you can sharpen. The knives I carry rarely go beyond the ability to slice fine paper. At this level of blunting I can restore them with just a few passes on a 600 DMT stone which is a typical finish I use on many knives. The speed of sanders is typically around 50 ft/s so you would need to really move the blade fast across the belt to keep the abrasion to that level.

So for keeping a blade sharp it tends to be overkill when you are just restoring high sharpness, except maybe if you are only using very fine buffing compounds such as Fikes demonstrates in his video which is why people who use high polishes tend to like belt sanders or buffers. However if you are resharpening really dull blades, the kind that you wonder why people are even carrying them because they are not much of a knife anymore, then belt sanders work very well because about 1-2 pass per side tends to refine the grit from one belt to another. So you can reshape and then sharpen them very quickly and efficiently.

As a side note, you can get convex edges on benchstones if you want. This is how traditional full convex ground parangs are sharpened.

-Cliff
 
Cliff Stamp said:
As a side note, you can get convex edges on benchstones if you want. This is how traditional full convex ground parangs are sharpened.
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Just out of curiosity, how is this done?
 
Lee Valley sells 15 micron SiC belts for 1x30 sanders, so removing just a tiny bit of steel is pretty easy. They also have 500 and 1200 grit Aluminum Oxide belts, so even fairly dull blades can safely be sharpened with little steel removal. Using a light touch is a good idea in any case. The finish on such an edge is close enough to polished to satisfy most, including me. It is very easy to use a belt sander for a light touch up with little wear on the blade. Just using the stropping belt with a little polish suffices for most blades that aren't in really bad shape.

An important point is where on the belt the edge is held. The Harbor freight sander has a very short platen near the bottom of the belt in front. Using the area just above the platen gives you a slack belt effect without it being too rounded. You can achieve the same effect near the idler wheel at the top. One nice thing about this setup is that you can look down on the belt from the top and see the angle of the blade against the belt.

This isn't rocket science. Just common sense.
 
There are two basic ways. On knives which have a large curvature in which the angle changes say from 10 degrees at the shoulder to 20 degrees at the apex then you rock the knife over the bevel and just feel the curvature. This sounds very difficult, I thought it was impossible the first time I was told it but then watched it done with a file right in front of me. The only problem with it is that there can be a tendancy to roll the stone too much and thus increase the edge angle.

I periodically check the edges on my knives sharpened like this and after a year or so they will have drifted a little. This isn't huge, but if I don't catch it, then it just gets worse. I let my small Bruks axe go for a few years for example and it drifted from 12-14 at the very edge to well over 15. Just keep an edge on the bevel and if it gets too steep then flatten it back.

The second method just takes into account that you are not a machine and the stones you use generally not perfect. For example if I sharpen a knife on a 200 grit waterstone stone, the stone wears so fast that by the time I have reground the edge there is also a hollow in the stone which increases the apex angle by 1-2 degrees per side. Generally all hand sharpening tends to increase some degrees of curvature because of the variance from pass to pass and the give of the hone. Generally this is so light that guys like Hossom would not call convex because they look flat and the curvature is really light and they have a point, they are generally not what people mean when they say convex edges.

-Cliff
 
Jerry Hossom said:
Lee Valley sells 15 micron SiC belts for 1x30 sanders, so removing just a tiny bit of steel is pretty easy.
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I can take a knife down to about 5% of optimal sharpness (measured not estimated) and it can be restored to optimal with 1-2 feet of travel over the entire blade on a 1" wide abrasive. This is for 1200/600 DMT, it is way less with the x-coarse which is pretty much 1-2 passes per side on a small diafold.

This is also pressing very light on the stone, about 250 grams or so. I press harder during shaping, but sharpening is really light. Now in order to get the same amount of grinding on a belt sander I need to move the entire blade fron one side to the other in less than half a second. Any longer will grind off more material. It is just basic math.

This is with optimal multi-beveling of course, if you are just stock bevel sharpening it takes longer to grind on stones and one pass on a belt could likely be about the same as minimal metal removal with really fine belts assuming that is the finish you wanted of course. However single bevel sharpening is really inefficient for many reasons.

-Cliff
 
Cliff- In order to better understand both the procedures you describe and the efficacy of your edges it would help if you gave some characteristics of "optimal" and its range. Also, I'm currently trying to evaluate a particular sharpening method myself and your "standard" would be an intersting rubrik.
 
Jerry Hossom said:
I don't know what you mean by "single bevel edge". The belt produces a convex (parabolic) edge.
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In the above I was using it to mean you are sharpening the entire edge. Generally this isn't needed or overly efficient as the very edge, last fraction of a micron does the cutting so only it needs to be at the required cutting finish and only it actually wears, again assuming just cutting and no visible gross damage from chopping or cutting metals/bone.

Lee has a nice discussion of this in "The Complete Book on Sharpening". The separation of shaping/polishing makes a major influence on sharpening, it completely obliterates grindability as a concern for example because with the right use of microbevels S90v sharpens pretty much just as fast as 420HC as they are both pretty much instant even as noted when they are very dull, <10% of optimal sharpness.

sputnick said:
... if you gave some characteristics of "optimal" and its range.
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I set optimal at the best blades I have seen including those hand sharpened by Ben Dale, Dozier, etc. . The sharpness is measured by push cutting light thread or slicing light cord under a specific amount of tension, it isn't some subjective judgement. Here are some knives so measured :

http://www.physics.mun.ca/~sstamp/knives/blade_testing.html#sharpness

In the above I was specifically talking about slicing sharpness, here is an example of such a measurements used to determine edge retention :

http://www.bladeforums.com/forums/showthread.php?t=416896

-Cliff
 
A polished surface across the entire convex greatly improves cutting efficience by reducing friction as the edge moves through the material being cut. In fact it's one of the primary reasons convex edges are useful, particularly on harder materials like wood.
 
Holy carp! Jerry Hossom and Cliff Stamp agreeing in the same thread?! March ebbtide and Kohai999 in here and it will be the end of days. :eek:

Jerry,

Maybe you should start getting kickbacks from Harbor Freight. Over at KFC, the belt-sanding crew co-opted at least one professional sharpener. He paid it forward by mentioning a cloth-backed 600 grit SiC belt he got from a&h abrasives. It leaves a very nice, uniform finish after the first few sharpenings and works well edge-up and edge-down (I remember the first/last time I tried edge-up with the 15 micron belt. :eek: pop!).
 
Jerry Hossom said:
A polished surface across the entire convex greatly improves cutting efficience by reducing friction as the edge moves through the material being cut. In fact it's one of the primary reasons convex edges are useful, particularly on harder materials like wood.
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This has actually been measured for wood and it is false, Lee cites the references in his book. The effect of friction is actually a *really* small component of the force in general. The main ones are the direct force against the bevel and the wedging forces against the blade. This is because in general most materials have a very low coefficient of kinetic friction against steel but have a very high internal rigidity, wood especially so. You can for example take a very coarse edge finish, x-coarse DMT, and easily chop it into newsprint and do a straight push and the friction isn't even high enough to fold the paper.

It should be obvious when cutting wood that the friction is a very low factor because if you consider how easy it is to push steel across the polished surface of a clean cut compared to the massive force it takes to actually push the wood apart to actually allow the blade to pass through it. Just physically do these two actions and see how much larger one is than the other, now go look up the relevant material properties and see how they compare in terms of the force. Even materials with a relatively low stiffness and a high coefficient of friction (styrofoam) are still lopsided so much that they will heavily favor a reduction in profile over an increase in polish.

These forces against the edge and binding on the blade dependent on the sharpness and blade thickness/profile respectively. Some materials have a low dependance on sharpness/profile such as cheese for example, but most materials are much more sensitive to edge sharpness and blade profile than the finish of the blade above the edge. How much of the profile is a factor depends on the ability of the material to sustain binding forces. Most ropes for example are very shallow binding and thus pretty much only the angle of the edge is critical. Styrofoam insulation however will bind across the full contact almost to a uniform amount.

As well for slicing you want a rough surface anyway, and the scratches above the bevel actually increase the cutting ability, again this has been studied, see Furi for example. What you are seeing here is basically an influence on the side scratches effecting the nature of the blunting plus basically moving the material during the cutting. Convex bevels also don't have an inherent greater lower friction than other bevels. In general the convex bevels which cut well do so because they are of lower cross section. It isn't like if you took a blade which was ground at 20 degrees and convexed it so the apex angle was 25 degrees it would cut better. Swaim hashed all this out on rec.knives over ten years ago and noted the focus should be on the edge angle and thickness.

-Cliff
 
Well, I didn't write a book, but work I did with some people in the woodworking industry contradicts Mr Lee. On chisels, polished convex edges increased cutting efficiency (as did CPM-3V compared with current steels being used). In fact when they went back and looked at some of the older tools that were credited with using "superior" steels, they found what was really improving their cutting qualities was that after some years of use and hand sharpening, the edges would become convex and well polished.

As for the rest of what you've written, my experience and that of some other knifemakers differs from yours.
 
Cliff,

Lee also talks about belt sanders in his book... even metal removal. For example, he states: "Fortunately, you quickly get used to the actions of the belt sander and will find that you can easily sharpen knives at the rate of about one a minute on the machine without excessive metal removal." (p. 92, empahsis added).

I'm also curious... where specifically is this in Lee's book?... This has actually been measured for wood and it is false, Lee cites the references in his book. I couldn't find it... but I sure find numerous examples of him sharpening items to a mirror finish.

cbw
 
CBW interesting. Yes I have a hard time believing what Cliff says people say like, Lee Swaim and others, have said when Cliff doesn’t even correctly quote and misrepresent posts in the same thread. As for blade polish above the edge I have noticed a difference. Try cutting a lot of tape with a polished bevel and then with a scratched one. It does make a difference in the real world. I’ve really done it myself no lie, no rumor and I’m not misinforming I really do notice a difference.
 
Jerry Hossom said:
On chisels, polished convex edges increased cutting efficiency.....
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Without knowing the chisel geometries being compared, I find that hard to believe. If the convexed chisel is ground more acute, which I'm guessing was the case, then yes cutting efficiency should be better, but that isn't a fair comparison. If the final edge angle is the same, the only advantage you might see if convexing the remainder of the edge for relief would be if you were using the chisel improperly and removing way more wood with a single cut than any serious woodworker ever would ..... and even at that, I think the hollow ground chisels many prefer today would outperform a convexed one.
 
Well, I might be lying but I don't think so, and if you choose not to believe me that certainly is your option. I don't know what kind of chisels they were comparing. I do know there were very serious woodworkers. The studies they did of various steels in planer blades were fairly sophistocated.

Here's a page on Lee Valley's website that links to all their chisels. I can't tell which ones are hollow ground. http://www.leevalley.com/wood/page.aspx?c=2&cat=1&p=41504

Here's a similar link from Highland Hardware.

http://www.highlandwoodworking.com/index.asp?PageAction=VIEWCATS&Category=254
 
C'mon, Jerry, I wasn't saying that you were lying, but apologize if it sounded that way. I was just saying I couldn't accept the conclusion that "polished convex edges increased cutting efficiency" without knowing more about the chisels and edge geometry. You've said now that you "don't know what kind of chisels they were comparing" and I accept that.

BTW I didn't see any convex edged chisels on the websites you linked to. In fact I've never seen a convexed chisel, or heard of a woodworker who would tolerate a chisel or plane sharpened that way.
 
cbwx34 said:
Lee also talks about belt sanders in his book... even metal removal. For example, he states: "Fortunately, you quickly get used to the actions of the belt sander and will find that you can easily sharpen knives at the rate of about one a minute on the machine without excessive metal removal." (p. 92, empahsis added).
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Yes, I thought that way myself for some time until I started looking at edges under magnification and determined just how much of the edge was damaged given a particular state of blunting. Even when taken to very low sharpness, 5% or so of optimal slicing aggression, you are often seeing on the order of 50 microns of metal lost and this is only the coarse stainless steels like S30V which blunt by micro-chipping. On the very fine grained tool steels the metal wear is actually much less.

Years back I started sharpening and measuring the sharpness in steps after passes on the hone and determined as noted in the above that it takes very few passes with optimal microbevels, it is pretty much instant. The math is very simple as I noted in the above. A belt sander turns so quickly that basically every second on the belt equates to 100 passes on a small stone. This makes it obvious that you are removing far too much metal unless the edge is heavily damaged.

The problem is guys who look at the edge after sharpening on belts and visually check and of course it isn't like you see too much metal is removed. If you needed to remove 25 microns optimally and instead took four times as much on the belt sander you would still never see it by eye as you can't tell a blade which is 3.0 cm wide compared to 2.99 cm wide. However if you compared the before and after after extended sharpening it becomes obvious because you are wearing out a blade four times as fast.

This was also discussed in detail with the relevant math years ago on rec.knives during a discussion about steeling a blade to minimize metal loss and just how much metal was lost during optimal hand honing with abrasives. Swaim noted just how little hand honing is required which is why he didn't support that steeling was needed and I did some math and provided some numbers to support his assertion and then did an extended comparison.

I'm also curious... where specifically is this in Lee's book?...
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In chapter two which he devotes to how wood is cut he focuses on how the thickness of the blade and the sharpness is what controls cutting ability. He states immediately that you should ignore friction. In the chapter on sharpening chisels he notes why this assumption is a valid one and why you can microbevel and only finish sharpen the very edge which is how serious wood workers sharpen chisels. The reasons why friction can be ignored is that you are cutting with large rake angles and when sharpening the grind lines are perpendicular to the edge and thus surface roughness makes no influence if if friction is significant. This refers to published peer reviewed work.

Jerry Hossom said:
As for the rest of what you've written, my experience and that of some other knifemakers differs from yours.
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Yes, that is always a good baseline, vague anon references :

http://www.cashenblades.com/articles/lowdown/lowdown.html

How many well known knifemakers have had the claims they make exposed by the actual science and facts in that article. Cause and effect is not trivial to link. In your comparisons what statistical methods were used to make sure the correlations were not only actually on the right variables but were actually significant. Did you do blind tests, or did you actually tell people they were working with a superior steel/geometry/finish and then expect this to not bias the results. What in fact exactly was compared? What it made sure when you were comparing bevels they were exactly the same in geometry and only the polish was different, or did you use a multi-variable model to insure the correlations were correctly attributed.

Dog of War said:
In fact I've never seen a convexed chisel, or heard of a woodworker who would tolerate a chisel or plane sharpened that way.
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I have sharpened a lot of chisels which were convex ground due to sloppy hand grinding. You just grind them back flat and micro-bevel at the required profile. You see the same on a lot of wood working tools unfortunately now because most of them are more utility than wood craft optomized. Typical hardware store axes have really thick convex profiles. The first thing you have to do to make them cut well is not polish this really thick bevel, you have to cut off all the unnecessary metal. Get the profile to the right cross section then polish the very edge.

Some draw knives are convex ground as they are used to cut contours so you want to be able to rock the blade in the cut, some small chip knives are the same. Generally with most wood working tools you don't want that ability. If you are felling a tree with an axe for example do you really want it to have the ability to easily rotate in the wood, or do you want the grind to act to stablize its movement in a straight line. As an extreme example try to cut wood with a splitting maul and note just how easy it glances and how horrible the penetration is even when the bit is fully polished such as on the Bruks maul. That has a full convex grind, does it cut wood well, of course not because it is way too thick.

-Cliff
 
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