A common sharpening problem (buffesr)

[Cliff Stamp]

Awhile ago I made a post about a significant sharpening problem :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=268630

this is the same thing Thombrogan noted in the recent thread :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=280672

There is another very similar problem which I have experienced many times before and rather strongly recently.

The first time I sharpened the S30V Military it refused to get sharp. I was using waterstone and checking the edge angle with a marker. The stones were hitting the entire edge fine, but the blade would simply not get sharp. It was taken right up to CrO with low sharpness (less 50% of optimal). However with Diamond plates it sharpened in no time, the conclusion seemed obvious - waterstones and S30V don't mix. Just last night I was sharpening a new custom with an unfamiliar steel and the same thing happened with the waterstones. The edge could be seen to be clearly getting abraded using a marker but it would not get sharp.

Inbetween the sharpening of those knives. the Military was honed with Waterstones and got it just as sharp as with Diamonds, sharp enough to readily shave with no effort and push cut newsprint. This was achieved because the stones were *lapped flat* before the honing. When honing with dished hones (not huge hollows, just barely visible by eye) the edge will take a matching curvature, effectively a secondary bevel at the very edge. While usually small (0.1-0.2 mm deep) it still makes a huge difference when you switch stones. Unless the curvature is the same on all the stones, as you move to finer ones the passes will no nothing until you have honed the entire bevel down and removed the secondary edge bevel. This takes a *long* time, far longer than it takes to remove the scratches left be the more coarse hone.

Checking the progress of the new knife once I switched from 200 grit to 800 grit I saw that the edge bevel was not getting honed in the last 0.2 mm. I then flattened the 200 hone, recut the edge and went back to the 800 hone. This time it worked fine and the edge that was produced would shave though a bit scratchy. I then worked to 1000,4000 and the finished on CrO to produce a fine shaving edge. So the short of it is to lapp your stones fequently to prevent the above frustration. Along these lines this is why I think buffers should be destroyed, as they make resharpening *very* difficult and problematic when not using power equipment, especially for novices and they are one of the primary reasons for the propogation of several knife myths.

Buffers hit the very edge bevel creating a secondary edge which isn't visible by eye and thus has all the above problems. In addition such edges are rarely done right and frequently have burrs (which go dull quickly leading to the myth of high sharpness = low edge retention or durability) and are over buffed and and too smooth with no aggression. However even when done right and the edge is left very sharp they still pose significant problems when resharpening on manual equipment. Consider the following :

Step 1 : The user gets such a knife dulled and goes to resharpen it, he matches the edge angle using a marker and a jig and carefully hones until all the marker is gone. The edge is checked and found not to be very sharp, but that is ok because the stone is coarse (**KNIFE MYTH** even very coarse edges can be very sharp and shave)

Step 2 : A finer stone is hauled in to clean up the edge. Again the edge is checked on a marker and all the scratches polished off, the edge cleanly reflects light and has a mirror finish. However it still doesn't shave. What can the user conclude? Usually that the steel sucks or the stone isn't the right one.

The problem is the secondary edge bevel that he can't see and which will only be noticed if the edge is checked under magnification. Now lets assume that the guy is a bit more experienced and trys to take the edge down to a full burr. Since he has to basically reprofile the edge instead of sharpen it, this will take a very long time and produce a bad impression of the ease of sharpening of the steel (**KNIFE MYTH** sharpening is very fast even on horrible steels - shaping on the other hand can be very slow, but there are ways around that). Now to further give him a headache it is easily possible that during this long session that the stones get loaded or even rounded (it happens quite fast on coarse waterstones). Now when they switch to the finer stone which isn't rounded they get the above problem all over again.

Note all of this can be solved with use of a 10-20x magnifier which is essential for sharpening.

-Cliff

 

[Sando]

VERY Good post.

Thank you Cliff !!!

Knife makers need to consider this information - closely.

Also, most users don't think about honing or stroping vs. material removing on a stone.

A relationship with a custom maker should involve discussions about who is honing, who is sharpening, and what methods are going to be used.

If more folks understood your post there would be much less 'myth' and ill will.

Steve

 

[The Tourist]

I agree. I have kept a lighted loupe in my Edge-Pro case for over a year.

 

[RobbW]

GREAT post! Many thanks, Cliff. I've got a Sebenza on the way (if the east-coast blizzard doesn't slow it down too much!) and I'll watch for this with my ProEdge waterstones. I need to get a stronger magnifier.

 

[Don Luis]

An interesting and educational post, as usual.

Thank you Cliff.

 

[Nosmo]

Very interesting.

To my logic, this points to not only having flat laps, but also
a method of angle repeatability.

Any free hand sharpening is likely to result in excess metal removal
( secondary bevel) or excess edge sharpening ( unintentional edge angle increase ).

This exact angle repeatability at every sharpening session is what makes the Edge Pro such an outstanding system.
And for those that can not keep their hones flat, there are now diamond hones that fit this system perfectly.

My only problem with the Edge Pro is on highly defined re curves.
And this problem is surmountable with narrow and curved hones
that Ben Dale is now making available.

 

[Sando]

I posted this last week, but for freehand sharpeners here's a way to set the angle, perfectly everytime. You can even get the same angle year after year.

http://knives.mylamb.com/calc.htm

Works very nice and it only takes a dime to remove the burr.

---------------------------------
BTW like Cliff said (and I'm paraphrasing) a carefully constructed, consistent angle, will stay sharp longer.

Or to put it another way:

A cheap steel with a good edge will out last an expensive steel with an abused edge.

Steve

 

[WadeF]

I was going to order some extra stones for my Edge Pro. Mainly the 180 grit because it looks to be rounded. I know there is a way to flatten it, and I think my Edge Pro even came with some beads to use to flatten the stone. I can't find these beads anymore. Can anyone recommend a good way to flatten these stones and what I would need to do it?

 

[Nosmo]

Lee Valley sell a simple kit consisting of silicon carbide grit.
( $10) .
Also Ben Dale recommends ordinary sand.

I have a flat concrete building block ( $2.00 )
and I drag it out of the garage and sprinkle a light layer of
grit and use it dry.

Get the hone and run a felt tip line down its length.

Then rub the hone to be flattened on the grit layered surface
of the block.
They say that a figure eight pattern is what you need to aim for.
Keep an eye on the felt line to watch progress
and use a straight edge as a last check for flatness.

Quick easy job.

 

[Kevin Wilkins]

I think water stones are a waste of time for highly alloyed steels. Try the synthetic Misarka stones from www.fine-tools.com I use the white Misarka ones dry and they cut very fast, raise a nice burr that I take off with a hard, black Arkansas stone and then polish on the hard buffing wheel.

Forgot to mention, the Razor Edge Book of Sharpening is a must read if you want to learn how to sharpen a knife quickly and properly. I think amazon sells it.

 

[RobbW]

Kevin, a newbie question: which steels are highly alloyed? The most stainless or least? Thanks

 

[thombrogan]

Originally posted by Kevin Wilkins
I think water stones are a waste of time for highly alloyed steels.

Waterstones work on 1095, 154CM, 440C, D2, M2, S30V, and VG-10. Are those low-alloy steels?

 

[Cliff Stamp]

KnifeRat :

Kevin, a newbie question: which steels are highly alloyed? The most stainless or least?

You can get very high alloyed stainless and nonstainless steels. However in general, for cutlery steels, the stainless steels are of higher alloy content, and specifically in regards to sharpening have more and harder carbides than the nonstainless steels (there are exceptions of course like D2 and M2).

The MISSARKA stones are just made out of AO and SiC the same abrasives as in the Japanese waterstones. The main complaint that the site uses against such waterstones is :

It can be hard to find a good sharpening stone for
modern stainless steels, which are so difficult to
sharpen that even a Japanese waterstone will
sometimes gunge up and cease to work.We had
exactly that difficulty.

from :

http://www.fine-tools.com/kuns.htm

That is nonsense, I have worked even CPM-10V with waterstones and the above described problem doesn't happen.

-Cliff

 

[Roadrunner]

Thanks Cliff. I came to the same conclusion while using my Edge Pro recently. I've found it difficult to lap these stones, I'm thinking of getting that kit Lee Valley sells. Coarse sandpaper doesn't work all that well.

 

[Cliff Stamp]

Coarse sandpaper doesn't work well unless you buy really high quality sandpaper which makes little sense to me because you could be using that for sharpening in the first place. I use a concrete block and sand from the beach. Start with the most coarse stone and work your way to lapping the finest ones, as the sand breaks down as you progress which naturally fits in with the finer stones needing less lapping. Flattening the stone should take less than a minute on small stones like that.

-Cliff

 

[Jeff Clark]

I'm not sure I believe that the buffer problem is primarily a hidden complex (convex) bevel problem. The test cases that you site seem to always involve resharpening of a buffed edge. While the edge bevel will tend to be convex at the apex I suspect that there could be other peculiarities of buffed surfaces that complicate resharpening.

Do you have test cases that have an equivalent narrow convexity on the edges that were not produced by buffing to use as controls? Something produced by taking a blade honed on a flat surface that was subsequently stropped with a simple abrasive like SiC paper on cardboard. It would be very enlightening to see if the difficulty in resharpening was equivalent to resharpening a buffed edge. Is the quick fix for a buffed edge to strop it with a loaded strop?

I particularly question your estimates for the effects of a miniscule concavity on your coarser water stone. When I swag the radius of curvature it is enormous. The angle differences seem miniscule. I would only expect to observe the effect if you use an angle clamp on your blade that remains in place for all honing steps. Even then it seems like there must be something in the method (besides the dishing of your coarse hone) that biases the fine hone to a slighly lower honing angle than your coarse hone. If you use edge-forwards honing on your water stone maybe the higher edge drag on the coarser hone tends to rotate the edge downwards slightly more than the case for the fine stone. My solution would be to finish freehand or do something to bias my finish honing to a slightly higher angle than my coarse honing. One way would be to intentionally dish the finish hone. Another might be to reclamp the angle guide to provide a slightly higher angle. Do the rough honing with the clamp a few millimeters further away from the edge than when you do the finish honing.

I don't really understand buffing, but it seems to involve some different mechanisms besides simple ultrafine abrassion. I wonder if there is some plastic surface slipping going on that leaves an extremely high density of lattice dislocations in the surface. This might explain other unusual resharpening dynamics of buffed edges.

 

[Cliff Stamp]

Jeff :

I suspect that there could be other peculiarities of buffed surfaces that complicate resharpening.

There are lots of problems that can exist besides the effective secondary edge bevel, the edge can be burnt, overpolished and rounded, still contain a burr, etc. .

Do you have test cases that have an equivalent narrow convexity on the edges that were not produced by buffing

Yes, I have frequently recut edges with secondary edge bevels which I applied in various ways, crock sticks, sandpaper on leather etc. .

Is the quick fix for a buffed edge to strop it with a loaded strop?

If it was buffed correctly and the extent of blunting not too severe. Otherwise you need to use sandpaper of suitable grit and forgiving angle medium (leather) if you want to maintain the edge variability.

The angle differences seem miniscule.

They don't need to be very large. Lets assume your natural angle tolerance is 1 degree, meaning 95% of the time you are within 2 degrees of your goal angle, and 99% of the time you are withing 3 degrees. Lets further assume that the dished hone adds just 3 degrees to the final edge angle. This means that only 1 in 100 passes actually hones the edge, the rest just hit the shoulder. Random deviations like hand sharpening are fine, systematic deviations like dished hones cause massive problems.

The reason that this gets out of hand is the myth about sharp edges requiring fine stones which leads to grits being switched before the edge has been cleanly set. You see this myth all over bladeforms, it is common to hear statements (even from makers) like "I don't use weak shaving edges, coarse ground blades work better anyway". Not only are highly polished edges more durable, even at the coarse finish the edge should shave, if it doesn't it isn't properly aligned or cut and you are just making far more work for yourself when you switch prematuring to a finer grit.

Even then it seems like there must be something in the method (besides the dishing of your coarse hone) that biases the fine hone to a slighly lower honing angle than your coarse hone.

Even if they are at the same angle you will get the same problem if the initial edge had a secondary bevel which wasn't removed by the coarse stone, or which was removed but too so long the coarse stone developed a curvature. The coarser waterstones will also dish out this fast, I lapp my 200 SiC after every sharpening (small blades 3-5"). The finer stones much less frequently which means the curvatures they develop will be of significantly different degrees.

My solution would be to finish freehand or do something to bias my finish honing to a slightly higher angle than my coarse honing.

In general this is the optimal method for most sharpening. Use a coarse hone to reset the edge to some angle 1-2 degrees under the final sharpening angle, this is just a shaping step can can be done very fast. Now use a finishing hone to sharpen the edge which is a secondary micro bevel of suitable width and angle for durability.

The first time this is done the shaping step should be all the way to the edge mainly to make sure that no weakned steel or obtuse secondarry edge bevel remains from buffed edges but from that time on you only need to do it to such an extent to reduce the size of the secondary edge bevel.

Note the critical part here is that buffed secondary edge bevels can be very obtuse, I have seen them as great as 35+ degrees per side. So if you don't fully remove them with the shaping step, applying the secondary edge bevel at 22 degrees is going to take *much* longer than it should which can be compounded by burnt or other wise weakened edges. This is where you get people using 100+ passes on a Sharpmaker when it should take 1-3.

I wonder if there is some plastic surface slipping going on that leaves an extremely high density of lattice dislocations in the surface.

This is one of the problems if edges are buffed incorrectly. You will see edges which are highly polished but biased to one side showing extreme plastic deformation and of course which are now very weak. This comes from wanting the buffer to do too much work and using it to clean up a poorly conditioned edge. This doesn't have to be the case of course. I have compared the durability and edge retention of edges produced by high speed honing and hand sharpening on the same grit and they were identical.

-Cliff

 

[Daniel Koster]

Originally posted by Cliff Stamp
If it was buffed correctly and the extent of blunting not too severe.

Cliff - could you elaborate on what you mean by "correctly"? (just want to make sure I've got the right idea)

Originally posted by Cliff Stamp
Not only are highly polished edges more durable, even at the coarse finish the edge should shave, if it doesn't it isn't properly aligned or cut and you are just making far more work for yourself when you switch prematuring to a finer grit.

I'm with you 100% on this one.



Here's my question:
(pic included )

Many folks I know buff like #1. I buff like #2 - along the blade, rather than perpendicular to it (this is done using a to-and-fro sawing action). This has other advantages (outside of this discussion) but does it make any difference to the buffing you are speaking of?

I've noticed that a major problem with benchstone sharpening (ie. keeping the edge aligned) is the fact that most of it is done perpendicular (or nearly so) to the edge and unless you have a very wide stone (or a small knife ) you still have to make either multiple passes, or draw it along the stone. The exception is the thin rods/hones (sharpmaker, etc.) that are meant to be drawn along the edge. Still, though, the cutting action is not truly inline with the edge.

I should also mention that I buff to remove the burr and to polish the edge. It completely dulls the knife. I then go back to a fine micron belt and leather belt for stropping - which brings it back to sticky sharp.

 

[RobbW]

Thanks Cliff, appreciate the clarification.

 

[Cliff Stamp]

pendentive :

elaborate on what you mean by "correctly"?

The two biggest problems I have seen come from the same source, asking the buffer to do too much sharpening. You take an edge and cut it with a really coarse belt, so coarse you can see deep scratches on the edge and even feel them with your finger, there may also be a heavy burr on the edge as well. Now instead of going to a higher grit belt to refine the edge go right to the buffer with a high polish load and use it to try to get a mirror polish pressing hard to speed up the slow process. This produces all kinds of problems and if where several knife myths comes from. You can see the same thing in hand sharpening if you jump from an x-coarse hone to CrO loaded leather and strop it a hundred times or so to polish the edge.

Of course even if you do it right and just use the buffer to apply the final polish you still have the above problem of a possibly very heavy almost invisible secondary edge bevel. Buck had this problem back when they used soft wheels. You get a knife, match the angle and try to sharpen but you hit nothing but the shoulder because the very edge has a more obtuse angle which everyone has kept secret from you. Their new Edge 2000 method got rid of this problem by using much harder wheels to minimize the secondary bevel formation. They also used a more acute edge angle which means in general more people will hit it right away with preset jigs.

I've noticed that a major problem with benchstone sharpening (ie. keeping the edge aligned) is the fact that most of it is done perpendicular (or nearly so) to the edge

Yes, you want this arrangement for optimal tooth formation. Well to be really critical the angles should cross over from one side to the next. This I learned a few years ago from a native knifemaker who also showed me how to bias edges so that they cut optimally on a push or pull stroke or cut evenly on both.

The way you describe buffing an edge has none of the above problems as its influence is erased by the next sharpening stel. That is a prtty drastic step to remove the burr though. I have only needed to do that on some really low quality (usually stainless) steels which develop burrs which can be 1+mm wide.

-Cliff