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Why am I getting a concave edge on my skew chisel

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Forum topic by RalphCompton posted 10-12-2018 05:23 AM 366 views 0 times favorited 9 replies Add to Favorites Watch
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RalphCompton

86 posts in 2795 days


10-12-2018 05:23 AM

Topic tags/keywords: sharpening turning tools wolverine skew

Not sure what’s happening. I am very new at turning and sharpening turning tools. I have a slow speed grinder and the Wolverine set, including the skew attachment. I set the jig to get the correct bevel, set the butt end of the 1” skew in the appropriate socket, and move the skew left and right across the moving wheel. A few light strokes in the right pocket, an equal number of light strokes in the left pocket. I get a nice bevel on each side, but the edge is concave. Not a good thing. With the narrower skew chisels I don’t need to move them side to side to contact the wheel, and I get a straight edge. Been looking for an answer on you tube but no luck.

Ralph


9 replies so far

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Andre

2063 posts in 1952 days


#1 posted 10-12-2018 05:33 AM

Is the grinding wheel flat, did you dress it? The bevel should have a slight concave dependant on wheel diameter.

-- Lifting one end of the plank.

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hairy

2765 posts in 3678 days


#2 posted 10-12-2018 01:13 PM

It’s called hollow grind, caused by the shape of the grinding wheel.

-- My reality check bounced...

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LeeMills

600 posts in 1447 days


#3 posted 10-12-2018 02:12 PM

What they said… unless..
you are not talking about the 40° cutting bevel but the 70° across the tool.
This video states a problem if you press too hard at each end, maybe you are pressing too hard in the center?
On my jig the cutting edge slides straight across so this is only a guess.
About 30 seconds in.
https://www.youtube.com/watch?v=ziejM7dcNUE

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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Lazyman

2526 posts in 1533 days


#4 posted 10-12-2018 05:30 PM

EDIT: I just noticed that you said concave. I was thinking Convex. I that is correct, then my comment probably doesn’t apply.

I assume you are saying that the straight edge now has a curve to it? Just how curved is it? I don’t have this jig but it would seem to me that the design would lead to a very slight curve simply because you are moving the skew in an arc against the wheel. It might be more pronounced if the wheel isn’t flat?

Also, a curve won’t hurt the cutting action of the skew. In fact, some people intentionally grind the their skew with a curve and claim it actually works better. I haven’t tried it yet myself but I have been thinking about regrinding one of my cheap skews into a curved edge to give it a try. Here is an article about how to do it.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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RalphCompton

86 posts in 2795 days


#5 posted 10-13-2018 03:19 AM

Thanks for the responses. Yes, new grinder, new wheel. Both wheels slightly out of round. Dresser will be ordered soon, after I get back in town.

I get a nice, hollow, grind on the bevel. Completely satisfactory. It’s the 70 degree across the tool that’s the problem. Convex would be fine, but I’m getting a noticeable concave edge across the tool. Not good.

After reading the responses, and staring at my jig some more, I suspect some operator error as well as the wheel needing dressing. I need to move the edge left and right across the wheel because the edge is longer than the wheel is wide. Incidentally, I get a nice straight edge when doing a smaller skew that completely touches the wheel. After I get back and dress the wheel I will try again and report back.

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Lazyman

2526 posts in 1533 days


#6 posted 10-13-2018 10:52 AM

If that doesn’t fix it, a picture of the curve might help.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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PeteStaehling

68 posts in 1266 days


#7 posted 10-13-2018 11:19 AM

A couple things…

First, if you use a pivot type rest like a Wolverine and use equal pressure across the grind on a flat face of the wheel you will get a radius equal to the length of the handle. So not a lot of convex curve, but some.

Second, I am not sure why you assume that a convex curve is a bad thing. There are a lot of different ways to grind a skew, but I find that I like my most used skews ground with a bit of a convex curve. I do have a couple skews ground dead straight and do use them for some things, but 90% of the time I grab the curved one.

I am not an expert so take all that for what it is worth, but it has worked for me and I have see it work for some turners who are much more experienced and skilled than I am.

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RobbieB

10 posts in 370 days


#8 posted 10-13-2018 11:32 AM

He’s getting a concave edge, not convex. Seems like OP is moving the handle faster than the blade.

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PeteStaehling

68 posts in 1266 days


#9 posted 10-14-2018 11:54 AM


He s getting a concave edge, not convex. Seems like OP is moving the handle faster than the blade.

- RobbieB


OOPS sorry. I misread that. I am puzzled how that would even happen given the method he is using unless the wheel is worn and badly in need of dressing or maybe he is grinding the middle of the skew on the corners of the wheel off of the flat face.

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