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Sharpening Skews

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At a recent demo, the Demonstrator stated that when using a skew, catches can be minimized if it is sharpened with a convex bevel instead of being hollow ground. Does anyone have any experience along these lines?
John
 

john lucas

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I disagree. I have, and have turned with convex, flat and concave with micro flats (which is what I like). You can get a catch with any of them. It's more about finess of movement. By that I mean, with any tool, skew include, it's about staying on the bevel. If you come off the bevel so just the edge is contacting the wood, it will kick back.
Personally I find it harder to use the convex bevel because I don't know where it is. I feel like I'm searching for it. I'm also playing with the Johannes Michelson grind for a bowl gouge which is also convex. That's another question.
With the 3 skew grinds I don't notice any real difference when planing or cutting long curves or flats. When I start cutting beads I have a lot more trouble with the convex grind. At least that's me but I have been using a skew for a lot of work for a long time. I'll be interested to see what others have to say.
I also don't understand the best way to sharpen a convex grind without changing the cutting angle each time. If I push a diamond hone over the edge I'm sure I don't end up with exactly the same angle. I've also tried a belt sander by laying the skew down and lifting the handle. I feel like I'm not being repeatable enough to get the same angles. With the concave grind my angles are exactly the same every time because I use jig for the initial shaping. Then I use diamond hones setting on the 2 raised surfaces to hone the edge and this is extremely repeatable.
Still I'm willing to learn and still have the convex grind skew.
 
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At a recent demo, the Demonstrator stated that when using a skew, catches can be minimized if it is sharpened with a convex bevel instead of being hollow ground. Does anyone have any experience along these lines?
John

Was that Eli Avisera?

I know he is a big proponent of convex vrs concave, for the Skew. A few people I know have changed and say it does work well for them.

I like concave, it's just easier for me to grind..

Interestingly Eli is a big proponent of concave for just about every other tool.

TTFN
Ralph
 
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Jimmy Clews, also is a proponent of such a grind. During a demo/hands on a few years ago he explained his reasoning behind grinding a skew that way.

My experience is, it doesn't reduce my chances of a catch enough to make the change. I still have the skew that I ground that way but don't often reach for it.
 
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Would seem to me that a convex grind for the bevel would keep lifting the business end out of the cut if you tried to lay the tool down to plane. Having used one-sided very long bevel tools, I can verify that they are more likely to dig, but I think anything much beyond flat would be more trouble than it's worth. Concave grinds are about honing, not working properties.
 

john lucas

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Well I am certainly impressed with Jimmy Clewes and Eli Avisera. They are fantastic turners and that's why I tried and am still trying the convex grind on the skew. I just haven't made it work yet.
I really think that many of the skew arguments are based on shear practice. What I mean by that is people will tell me that they couldn't work with the skew. Then they tried the curved edge, or the convex bevel, or whatever, and now they can so they claim this worked for them. What I think actually happens is they just practice enough with that particular tool to learn to use it. If they had done the same with the other grind they would probably have learned that also.
My statement above also works in reverse. I'm used to straight edge and flat bevel so I try the convex grind and I'm biased toward the straight grind so maybe I'm not being as honest as I should be. I'm trying. I really have used the convex grind and trying to learn from it. Maybe with more practice I'll learn the to use it as successfully as I use the other grind. So far it doesn't work for me nearly as well. Wish I could work with Jimmy or Eli. The work they produce is truly spectacular.
 
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John,
I agree with you! Making toothpicks out of logs is the only way to get good with a skew or any other tools, well except maybe the easy*)*#'s. I grind my small skew with a very slight convex grind, I use this on pens and doing fine detail work, oh and it has a stright angle. All my other skews, two D. Thompson and the big one are concave and curved edge. If you practice they get easier, but only with practice. Good thing I like to practice! Oh I did a fun thing I put up screen material behind my lathe and in front of my work bench (like a curtain), man that makes clean up a lot easier and doesn't block the A/C.
 
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for what its worth here is my pitch. I sharpen all my skews but one with a flat grind on the side of an 8" wheel. Touching the bevel to the wheel takes about 3 seconds per side. It leaves a good sized burr you can take off with a slipstone, diamond hone or leather wheel (strap). One skew 1 1/8 inch I ground to a concave bevel on the flat of the wheel making successive passes, about 1/8 inch bevels each pass. Then round over with a coarse stone, fine stone and finish with a slipstone if desired. I am not much of a skew user and hence can screw up a piece quickly if not careful.

My mentor and many of the Denver areas mentor Pete Holtus told me about 6 years ago to use what worked BEST. Pete passed away about two weeks ago , he is and will be missed by literally hundreds of turners. A great wit as well as turner.
 

Bill Boehme

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At a recent demo, the Demonstrator stated that when using a skew, catches can be minimized if it is sharpened with a convex bevel instead of being hollow ground. Does anyone have any experience along these lines?
John

I think that the difference is psychological. The dimensional differences between concave, flat, and convex are trivial and the important thing is understanding how to handle the skew and what causes catches in the first place. It is probably a lot like professional athletes who do mostly superstitious things to get focused on the game like holding a bat or club a certain way, etc.
 

john lucas

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Bill I like the superstition analogy. It's kind of like comparing the edge of a tool using an 8" wheel or a 6" wheel. the hollow grind is only thousands of an inch different but it sounds good to say the 8" is flatter.
 
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I actually went and looked it up. Assuming a 3/8" bevel, the difference in "segment height" (how "concave" a hollow ground bevel is) between a 6" wheel and an 8" wheel is about .0015 inch. The difference between a hollow-ground bevel and a flat bevel is under .006 inch.
 
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which way??

I have all kinds of the darn things. All are ground with the concave shape, some straight, some radius, and one small 1/4 inch is convex.To me use of each requires a bit different presentation. The essence is presenting the cutting edge in a manor which will support the cutting edge preventing the old screw thread result. I consider use of the tool requires carefull attention to making sure the cutting edge is supported in most applications--exceptions do exist in some uses, such as the peeling cut.
I find no difference in presenting the convex to that of the concave grind except the former is harder to use in most applications due to the presenation of the cutting edge with necessary cutting edge support.
My experience tells me most turners I have watched use a concave grind.
 
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I've used the convex bevel on my carving chisels for decades. Reasons being greater control of the cutting edge as the "leverage point" becomes variable and off-center hits with the maul are no longer an issue, and chisel polish on the wood surface. Control of the cut is strongly enhanced when using either mechanical or pneumatic drivers.

I also use a polished convex bevel on my small detail gouge that I use to clean up the bottom of a turning as advocated by Ellsworth [see http://www.woodcentral.com/newforum/grinds.shtml ]

I've tried both convex and concave grinds on a skew. Don't see much difference except when working with punky sections in the wood; the honed convex surface leaves a more polished surface.
 
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I myself have not mastered the skew as of yet.
I have just purchased the Glenn Lucas DVD. In the sharpening section he sharpens his skews with the convex as versus the hollow grind.
One of the things he continues to stress is riding the bevel, no matter what tool you are using.
For new turners this is a good DVD to own and view time and again.
 

Dennis J Gooding

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Dennis in Southern Oregon

If you study the geometry of cutting with a concave ground skew, you will see that unless you are turning an object with diameter larger than about 71% of that of the grinding wheel (assuming a 45-degree shear slicing angle), only the part of the bevel immediately adjacent to the edge can contact the wood during a normal light cut. This is true also for a flat or convex grind. In order to cause cutting to occur with any of these grinds you have to rotate the skew to produce a positive entry angle, at which point the contact point moves back slightly along the bevel as the skew enters the wood. I believe that the main differences among these grinds lies in the amount of rotation of the skew that is required to obtain a given entry angle, starting with an initial angle of zero, i.e., the skew is tangent to the wood at the edge. The convex skew would require the largest rotation, the flat grind next, and the concave grind least. This suggests that the convex grind will require less precise control of the skew during entry and the subsequent cutting.

One additional, perhaps minor, disadvantage of the concave grind is that if it is over-honed with a flat hone, the immediate area of the edge will take on a reduced bevel angle that may it make to hard to start a cut.

Dennis
 
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Good information on edge versus wood here. http://homepages.sover.net/~nichael/nlc-wood/chapters/caop.html Sharpness and clearance angle are equally important in turning.

"Microbevels" are really convexities, and are increasingly mentioned by sharpening gurus of all persuasions. Do it on both sides and you get a backbevel too. Makes it a better high-angle cutter, but like all such, it'll feed a bit tougher.
 

john lucas

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Dennis That's interesting because it feels like I have to move the convex skew further to cut a straight sided bead. That's where I have the problems. The the flat bevel I don't have any trouble rolling over the edge and lining it up for the flat slide cut. With the convex ground skew I lose the cut going around the corner of the bead and then get a catch trying to find the cut again. I may have time to go into the shop on Sunday. I'll try it again.
 
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Dennis That's interesting because it feels like I have to move the convex skew further to cut a straight sided bead. That's where I have the problems. The the flat bevel I don't have any trouble rolling over the edge and lining it up for the flat slide cut. With the convex ground skew I lose the cut going around the corner of the bead and then get a catch trying to find the cut again.

As mentioned in my first response, you try to roll back on a convex bevel you lift the edge out of the cut. Think of a rocking chair.

Keeping a decent clearance angle when doing beads or pommel cuts is what keeps you from bruising the end grain, too.
 
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I've experimented with every conceivable grind for the skew, and have come to a few of my own conclusions. If I am doing traditional bead work, a concave or flat grind works well; the natural curve of the bead gives clearance to the back of the bevel, so there is no issue there. However, I don't like a curved cutting edge at all for this kind of work. The most useful parts of the tool, the heel and toe, have been ground away. If the skew is used mainly for planing cuts, the curved edge works ok.

I have experimented with convex grinds as well; I think many have trouble with it because the fulcrum point has moved from the back edge to the center of the grind, making the tool react quicker to user inputs. (Same as with a skew with a round bottom edge where it sits on the tool rest...the fulcrum point is now the center, not the edge of the tool. The round surface causes the tool to react quicker than a tool with square edges) I find in actual usage that the convex grind doesn't affect cutting beads; the back edge doesn't touch the wood anyway. The convex grind allows the cutting of coves, because the back edge doesn't have the tendency to lift the cutting edge out of the cut. That's similar to relieving the back edge of the grind on a detail gouge.
 
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