Saturday, April 4, 2009

Grinding and Honing the Skew (Video)

Something besides the skew is giving me trouble these days at the lathe! This is what I get during thunderstorms, and all the reasoning in the world doesn't seem to work.

Here is a video of grinding and honing the skew chisel.



Here is the edge part of the way through the honing process. You can see where the arrow indicates a small portion that the stone hasn't reached. It's vital to easy skewing that the entire edge be honed, so back to the stones. If I experience a catch (and it does happen, I assure you) I immediately check the edge. More often than not, I find a small area that has a burr or some other distortion. Think about the tracks left by a chipped plane blade, and the different force needed to push it. Now imagine that spot engaging a whirling piece of wood.



A few benefits come from maintaining such a large hollow grind.
The tool rides on two distinct edges while on the stone which helps maintain the correct position while honing.
The second is that the area being honed is so small that even a fine stone cuts to the edge quickly.
Also, the smooth stone offers less resistance while honing which increases the sensitivity to the contact between the tool and the stone, which may also help maintaining the correct position.

Below you can see a wonderful telltale sign of correct contact with the stone. You can see the distinct trail marks left where the edge and back of the bevel contact. It is always better to fault by having the edge of the bevel rise up, because it doesn't matter if the back part of the bevel is slightly rounded.



As usual, the real test of a sharp tool is to cut the endgrain of pine.


I feel like I can't stress the importance of sharpening enough when it comes to learning the skew. I can turn with a compromised gouge, but I can't create good turnings with a dull skew. I did check the geometry of my cutting edge and found that the radius edge is at around a 70 degree angle to the length of the skew and the bevels are around 25 degrees. It's the first time I've measured them. I generally look at the length of the bevel for information about its correctness. I know folks who turn beautifully with bevels so long that I get chills!

And as far as the radius goes, I like to keep it subtle so that I can still use the toe and heel of the edge easily. They come into play a lot in more advanced techniques, but we've still got a ways to go before that.

6 comments:

herman said...

Our dog George was 7 when we adopted him. He too came with a thunder phobia and for the first year or two me tried to calm him with words and affection. This helped not at all, in fact it seemed to make it worse. We gradually realized that we were in a way reinforcing his fears, so we tried something different. Whenever thunder or fireworks erupt, we simply carry on as if we can't hear it and we ignore his fear reaction, which is usually endless pacing.

Over time he began to settle down when he noticed thunder didn't affect us and now he is relatively normal. Just an idea you might try.

Otherwise, is that the 8000 grit stone you are using to hone the skew?

Herman

Anonymous said...

Peter,Thank you very much for the demo on skew shapening.I will try it tomorrow.Keep those tips coming.Now,One of my first windsors has a leg loose in the seat.What is the correct way to fix this without tearing up the finish? Thanx ,Kerry

Jeffrey said...

Wow! I reground my skew and honed it according to the video. Works wonderfully -- no catches and much better control!

Jeff L

Peter Galbert said...

Sorry for not responding more quickly to the comments, for some reason they didn't show up in my email as usual.
Herman,
I'm with you on the ignoring the fear idea, the only problem is that when she does settle down, it's between me and the lathe, but at least the pacing and panting is over! Yes, it is a 8000 grit stone that I've been using to hone the skew.

Kerry,

the answer to your questions depends somewhat on the glue that you used when you put it together. Hide glue can just be reglued, just introduce some fresh (preferably hot) glue into the joint. If you used yellow or white glue, your options are limited because they don't have the ability to glue to themselves. Perhaps epoxy would work best. If you used tapered tenons, you might find that the joint tightens nicely in the summer. I have an early chair (actually my favorite) that seasonally loosens in one of the legs, but it sits fine.

Jeff,
I'm glad that it helped, skews seem to have a lot of prerequisite steps to working well! I'll show more in the next video

gregoire68 said...

Peter, thanks for the blog and the tips. I am a noviced at turning but thankd to a big pile of toothpicks I am mastering the skew. You have mentioned your favorite sharpening tool being a Bear tex wheel. I've Googled it and found about 40 Norton Bear tex wheels. What grit are you using and who is the supplier? August 6th I start my first windsor chair with one of your collegues. Greg

Peter Galbert said...

Greg,
I use the finer of the two wheels offered by Bear Tex, you can get them at Highland Woodworking. Use them on any tool that you'd use a buffer, such as carving tools. Think of it as a cross between a grinder and a buffer. Good luck in your class!