Pull cut question

[hockenbery]

I have been using a pull cut with an Ellsworth ground gouge to true cylinders for 20 years.
maybe someone knows why it works.

this cut is similar to a skew planning cut with the point down
i was reminded with the @Neil S thread on wing angles that my wing bevel angle on my bowl gouge is close to my skews bevel angle.

what I don’t understand is why the bowl gouge makes this cut end to end - air to air - Leaving a smooth surface end to end. No catches or splintering coming into the endgrain from air
it has nothing to do with skill Because I have had beginners make this cut flawlessly in workshops.
its pretty much a catch free cut if the nose of the gouge is kept out of the wood.
i could never cut in from air successfully using a skew.

a few clips from a 3 sided napkin ring demo videshow this cut

a preview of the cut- This spindle is mounted on three centers to cut three faces. the to be napkin rings are separated by parting cuts






The cut starting in air cutting from the edge. No catch no splintering






The finished surface is pretty clean.



any ideas on why this works?
I have thought bar crossing the edge of the cylinder gives support to the cutting edge but It just a guess.

 

[Dave Landers]

Some thoughts...

The angle of the cutting edge, like the angle of a skew doing a similar cut, is shearing. So good, clean cut plus thus there's not much force to cause the gouge to "skate" backwards - easy to resist that force with your thumb/finger on the tool rest.

The bevel, even tho it's riding on the wood, is not supporting the cut - that is, it is not resisting that "skating force". But that is ok because 1) there's not much force pushing back, and 2) if the bevel is riding the wood, any skating is just going to disengage the edge from the cut.

In this case the bevel is "steering" the cut. Keep it on the wood and you'll make a cylinder. Lift the bevel a bit and the gouge will start a cove or cone (or dig in and catch). But it's pretty easy to ride the bevel so easy to make a cylinder.

Unlike a skew, any downward force on the gouge pushes it along the axis of the gouge (slides the gouge down) which tends to disengage the cut. With a skew, any downward force from the cut will try to pivot the skew, driving it into the cut (thus a catch). And also cutting with the wrong part of a skew edge (top) will want to twist the tool and slam it into the tool rest (catch).

 

[Brian Gustin]

What dave said - I'd bet if you could sharpen and shape your skew to match your wings on the gouge grind, your skew would work pretty good for the same cut too, although I suspect the difference might be at the tool control level from that point - With a skew you'd have to be "pushing" the bevel into wood, while with the pull cut you're "pulling" the edge along the cut (IMHO, better control when you pull than when you push - same way I'd deal with bolts & nuts when I was wrenching - less busted knuckles with pulling on the wrench than when pushing it..)

 

[Randy Anderson]

Well, I won't even attempt to explain the mechanics of it since I don't know what they are and I'm sure Dave is right but, I just put a spindle blank up and gave it a try. Worked like a charm with a nice finish. Only thing that comes to mind is it's like having a skew without a point that extends in front of the intended cutting area. On the gouge it's behind the cutting surface of the wing so doesn't risk getting into the action unless you just really go crazy and lift up on the handle and swing it in. Thanks. I learned something very useful today. I have a piece coming up later that I'll make good use of it on.

I do handle down sheer pull cuts on the outside of bowls and vases a lot and the mechanics of this are very similar but a bit different I think on spindles.

 

[Donna Frazier]

I believe, the gouge wing is acting more like a SRG than a skew. Either way, a plaining cut is a light volume cut that is different than a roughing peeling cut. A plaining cut is an unusual cut that is strictly horizontal across a spindles long fibers. The edge actually enters the sidegrain at an angle slicing. Instead of that edge getting underneath the endgrain as it progresses across the spindle, there is also an element of light pressure into the spindle, where along the edge it peels away the sidegrain ahead of the trailing slice. This prevents the slice from getting underneath (or into endgrain) and instead, allows the plaining cut to leave behind a nice finish.

To try to answer your question, a pull cut across a cylinder spindle has less pressure into the spindle compared to using a skew. Also the curved bevel edge of a gouge wing is less likely to slip below the fibers or into the interrupted cut...This may be why you find the gouge easier.

 

[Kirk Amidon]

There may be something to the idea that the bowl gouge being round is therefore more stable than a skew on an edge for this sort of cut. Much easier to maintain that sweet spot when the COG of the tool is closer to the toolrest. I recall that Stuart Batty mentions how the wing on a 40 - 40 is very similar to a skew, and that is one of the reasons he feels it is so efficient.

 

[Dean Center]

All of the above are interesting and thought provoking, but I'm not sure that they really answer your question, which was "why can I start from air and end in the air with the gouge and not a skew".

Your gouge has a slight convexity to the wing edge, much like a radius on the skew edge, but the gouge also has a curve relative to the axis of the tool, which the skew does not. This would further decrease the length of edge that is contacting the wood, and it would also better deal with the irregularities in the piece shown in the video. I will also point out that in your video, you have your fingers up on the gouge past the toolrest near the wood, and I bet you don't when you use your skew. Whether this is enough difference to explain it, I can't say.

My suspicion is that the biggest difference may be your perception, and your confidence. After all, what could be scarier than taking that long sharp skew edge and sticking it into end grand, right?

 

[robo hippy]

In theory, you can do that cut with any tool that has a cutting edge. The terms planing cut and peeling cut seem to be the same to me, but not positive. Same with push/pull cuts, which to me only difference is which side you are standing on.... As for why it works, not sure. I can do that cut with a SRG as well. The high shear angle is part of the reason why it works and leaves a nice surface. Maybe it is like Yogi Berra said, "It is 90% mental and 10% in your head."

robo hippy

 

[Donna Frazier]

Peeling cuts have bevel underneath the cutting edge for roughing. Slicing cuts have bevel behind the cutting edge for lighter finishing cuts. A plaining cut (horizontally across a spindle) is similar to a slicing cut.