Shear-cut tools/techniques

Discussion in 'Newbie' started by Jamie Straw, May 22, 2016.

  1. Jamie Straw

    Jamie Straw

    Joined:
    May 28, 2015
    Messages:
    1,440
    Location:
    Bainbridge Island, WA
    I was turning a dry, spalted maple bowl today, and it became evident toward the end of shaping the outside, I needed to shear cut if it was going to be anywhere close to smooth. I used my 1/2" bowl gouge, low and I think at a good shearing angle. Getting tool control good enough to sweep around even an 8" bowl is a challenge (especially without a curved tool rest). But I'm wondering about different ways to use different tools for shear cutting/scraping on difficult wood. Can we consolidate some tips here in this thread?
     
  2. hockenbery

    hockenbery AAW Advisor Staff Member

    Joined:
    Apr 27, 2004
    Messages:
    4,304
    Location:
    Lakeland, Florida
    Home Page:
    The cleanest cuts remove very little wood. First you need a smooth surface to clean up.
    Then we have terminology.

    There is "shear angle" that presents the cutting edge at 45-80 degrees to the rotation of the wood.
    "Shear cut" for most turners is the flute up cut on the front edge of the wing.
    But I have heard "shear cut" used to describe many different things.

    A pull cut with the wing of the side ground gouge gives me about the cleanest cut I can get with a gouge.
    The bevel angle of the wing of the Ellsworth grind is 25-30 degrees really sharp.
    Only works on convex curves and there is minimal bevel contact so little bevel drag.
    The lower the handle the higher the "shear angle". I usually try for about 45 degrees.
    I use this cut on the outside of natural edge bowls as well as problem woods.
    Most of the time it will cut the barks edge cleanly and the bark has nothing behind it but air.
    It Is also excellent on an interrupted cut.

    "Shear cut" A very advanced technique is the "Shear cut" which is made on the front edge of the wing, tool level, and the flute straight up.
    Very advanced cut because it is a so close to a major catch position. The cut works best when when the tool is held loosely.
    the Ellsworth grind make a shear angle of about 75 degrees. There is minimal bevel contact and the cut only removes a small amount of wood.
    It is well worth having someone teach you this cut. It works on both convex and concave curves.
    I use it a lot if I need to make a cut on a bowl toward the Chuck since it cuts the wrong way fairly cleanly.

    The push cut with the tool rolled to about 45 degrees gives a shear angle as well which will surface most woods.

    Al

    Al
     
    Last edited: May 22, 2016
  3. hockenbery

    hockenbery AAW Advisor Staff Member

    Joined:
    Apr 27, 2004
    Messages:
    4,304
    Location:
    Lakeland, Florida
    Home Page:
    I don't use curved tool rests. Some people swear by them and I think scraping sort of demands a curved rest.
    Curved rests limit shapes and get in the way more than they help.
    When I think of the 20 or so local turners here In Florida that get asked to demonstrate only one uses a curved tool rest.
    For him it is important and it works.

    With a gouge, tool control comes from having the handle of the tool against the body and riding the bevel.
    I make the curves with body movement.
    Weight shifted from one foot to the other and turning my body as I cut.

    Shaping a large bowl between centers.
    I point my left foot in the direction I'm cutting and far enough out so I won't be leaning at the end of the cut.
    I start cutting at the weight on my right foot right hand forward left hand holding the tool against my side.
    As I cut to the rim I shift my weight from my right foot to my left turn my body and shoulders to make the curve.

    I do use a Robust "j" rest inside large bowls. It only has a right side so I can work closer.
    The gouge only rides on the straight part.
     
    Last edited: May 22, 2016
  4. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,865
    Location:
    Eugene, OR
    I guess there can be two different cuts here, one is a shear cut, which implies a bevel rub, and the other is a shear scrape, which is pretty much the same cut but the bevel is not rubbing. This one to me is not a scrape at all, but is called that because the bevel is not rubbing, but I can't think of another name for it. This is a video I need to do, and have some things to ponder before I take it on.

    Here is one that is fairly good: https://www.youtube.com/watch?v=tZ0utpU9Aik

    Shear refers to angle. Scraping cut is the scraper flat on the tool rest, and the cutting edge is at 90 degrees to the rotation/spin of the bowl. You can use scrapers, gouges laid over on the side with flutes at 90 degrees, or skew chisels/negative rake scrapers. The idea with the shear angles is like speed bumps in the parking lot. Hit them square on (scraping cut) it can be a sharp bump. Hit them at a 45 degree angle, and the bump gets smoothed out. Hit them at a higher angle and the bump is minimal. With cutting edges, scraping is rather blunt and tends to pull. The higher shear angles are better at gently lifting the shavings off the wood than shaving cuts.

    Jimmy Clewes was the one who got me thinking about shear scraping for the finish cut. His comment was some thing like 'if you have a bevel rubbed finish, then when you start sanding, first thing you have to do is cut through the burnishing'. This is why my preferred cut is a shear scrape. My favorite tool on the outside is a swept back scraper. It is easy to drop the handle and get a shear angle in the 70 to 80 degree range. Another benefit to scrapers over gouges for this cut is that with a gouge, you have to roll the flutes over till you can barely see the edge cutting, if you can see it at all. With a scraper, the cutting edge is easily visible. I always do this as a pull cut, and move with my body, which is Thai Chi 101. Now, depending on the wood, the burr can make a lot of difference. On softer and more punky wood, I am really liking my fine CBN wheels, 600 and 1000 grit. Lousy edges for roughing, but excellent for clean up in figured and softer woods. They will clean up things that the 180 grit burr won't. A gouge that has more of an open flute (Doug Thompson's fluteless gouge, or a spindle/detail gouge with a ) nose), and a 600 or 1000 grit grind on it also will really clean things up that the standard more closed flute designs can't do because you can roll them over on their sides for a higher shear angle. You can get close to those angles on the outside of a bowl by dropping the handle, but impossible on the inside of a bowl.

    The inside of a bowl is more difficult. Bowl rim, tool rest, and lathe bed can all get in the way. Gouges are totally out as far as I am concerned. You can use a ) nosed scraper, which is my favorite tool here. Drop the handle a bit, and only contact on the lower half of the tool so it doesn't tip over and catch, kind of like when using skew chisels. Again, a pull cut.

    Now another advantage of shear scraping is that you can get a piece almost perfectly round. Since you are not rubbing the bevel, you are just taking off the high spots till the piece is round. When rubbing the bevel, you always get a little bounce, part of which is from grain orientation as the cutting edge works differently going with and against the grain. Tool pressure can contribute here as well as a hollowed out bowl being some what elastic, so all of these keep a bevel rubbed finish cut from being perfectly round. Not a problem big enough to notice unless you are trying to go less than 1/8 inch thick.

    For tool rests, on bowls I always use a curved rest. One practical reason is that you just don't have to move the banjo and adjust and pivot the tool rest as often. They do make it easier for one continuous cut from base to rim, and from rim to bottom of bowl. The J rests and the 1/4 arc of a circle rests work. I prefer a S shape. The only one out there that I think has perfect shape for inside bowls is a blue cast metal one that Craft Supplies sells. It needs hardened drill rod on it.

    I may have been doing hand honing all wrong these last years, but for sure the fine grit CBN wheels took it up a notch or three...

    Hmm, I did run on there a bit didn't I???? As I said, getting ready to make a video clip of it...

    robo hippy
     
  5. John K Jordan

    John K Jordan

    Joined:
    Feb 2, 2016
    Messages:
    136
    Location:
    East TN
    I use shear scraping a lot, either with a bowl gouge with swept back wings, a spindle gouge, or a shear scraper (the other John Jordan sells a nice one.)

    For another way of shear scraping, I used this on recent turning: Hold the gouge upside down and begin shear scraping then move to scraping into the bottom of a tight coves. This worked well. I'm sure others have done this but it was an invention for me.

    scraper_gouge!.jpg scraper_gouge2.jpg scraper_gouge3.jpg

    The end result:

    elm_box_comp.jpg

    JKJ
     
  6. Jamie Straw

    Jamie Straw

    Joined:
    May 28, 2015
    Messages:
    1,440
    Location:
    Bainbridge Island, WA
    Thanks!

    Lots to digest here, and no brainpower tonight, but I appreciate it and will read through thoroughly. I knew there'd be shear-cutting and shear-shaping info, and I appreciate how detailed your posts are.
     
  7. Bill Boehme

    Bill Boehme Administrator Staff Member

    Joined:
    Jan 27, 2005
    Messages:
    8,125
    Location:
    Dalworthington Gardens, TX
    Home Page:
    My definition of shear is in agreement with what Reed says ... it's the angle that the tool meets the wood. Like Al said there are many interpretations of what a shear cut looks like so I'll describe what I call a shear cut. Jamie, maybe there are as many interpretations as there are woodturners.

    As a starting point, if you are familiar with David Ellsworth's shear scraping method that he shows in his bowl turning DVD ... that is very similar to my technique for shear cutting ... the main difference being how the edge is presented to the wood. With shear scraping, the tool is in a shear angle rather than being straight across the movement of the wood and the tool is rolled way over so that the top edge of the flute is nearly closed while the bottom flute is removing gentle wisps of wood. The pressure is only against the tool rest and barely brushing against the wood which enables the tool to true up any slight out-of-roundness that might exist.

    The differences with shear cutting are that I have the handle really low ... sometimes the handle is dropped as much as perhaps 80° below horizontal and instead of having the tool rolled over with the flute closed as in a shear scrape, begin by placing the bevel flat against the wood. Picture in your mind the tool rest low and the tool pointed steeply upwards anywhere from about 45° to 80° with 60° being roughly the middle ground. Put away your protractor ... this is a touchy-feely thing not a scientific precision measurement. Of course you know that you can't cut wood with the bevel flat against the wood, so very slightly roll the tool towards the cutting edge and as soon as the shavings begin, that is the shear cutting position for the tool. It's a bit like using a skew in that respect. In fact, you could theoretically shear cut with a skew although I wouldn't recommend it for cross grain turning.

    About tool rests: I'm with Al ... I have some curved rests that never get used. I much prefer the straight rests. Here is how I use them on the exterior of a bowl for shear cutting. The rest is angled so that it is almost touching the wood at the finish of the cut. The cut is a pull cut starting from the foot end of the bowl and ending at the rim end of the cut. Don't try to do the whole thing in one single continuous movement. I rarely am able to fo it in one continuous sweep. This means that the rest usually isn't close to the wood at the beginning so the tool will be extended well above the rest and cutting high on the wood. You need to be mindful of the cutting edge because it needs to follow the curvature of the wood and shouldn't be held rigidly in one position. The Thai Chi analogy that Reed mentioned where your body follows the flow of the curve is a great way to describe how to move your body to control the tool movement. Before actually making the cut, I plan my movements to make certain that my ending stance is a normal comfortable standing position.

    When I took a class with Joe Ruminski, his shear cutting method was about half way between what I do snd what Al does.
     
  8. john lucas

    john lucas

    Joined:
    Apr 26, 2004
    Messages:
    5,822
    Location:
    Cookeville TN USA
    Are you talking shear cut, or shear scrape. Grantes a properly done shear scrape removes shavings and is therefore probably a cutting action. I call it a scrape because its not a bevel rubbing cut. I call a shear cut a bevel rubbing cut with the cutting action being at a somewhat steep angle.
    I have a video showing shear scraping. Dont know how to save and post a youtube link from my phone but if you go to youtube and type in john60lucas/shearscrape it should bring it up.
     
  9. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,865
    Location:
    Eugene, OR
    Here you go John:

    https://www.youtube.com/watch?v=7oeiVQLeOd4

    Haven't seen it in a while. Interesting in that for the first part you are using a negative rake scraper. I have done that as well, figuring that since when they are used as scrapers they take very fine cuts, maybe when used as a shear scraper, they would do better than standard scrapers. Well, I didn't notice any difference.

    The shavings taken with shear scraping are very fine which allows you to go uphill or down hill. How fine? Like my Grandpa would say, 'That's finer than frog fur!' 'But Grandpa, I have never seen fur on a frog!' 'That's because it is so fine!'

    If you have talked shear scraping with Lyle Jamieson, he says it is 'sheer' not shear. Kind of teasingly, I asked if that was because the shavings were so fine and light, kind of like the nightie you want the missus to wear?. No, no, no, like the sheer face of a cliff. Oh well it is pronounced the same way...

    Being a scraper psycho, I always wonder why people say that scraping is not cutting? I get lots of nice shavings, depending on the woods. A scraping cut for sure...

    robo hippy
     
  10. Bill Boehme

    Bill Boehme Administrator Staff Member

    Joined:
    Jan 27, 2005
    Messages:
    8,125
    Location:
    Dalworthington Gardens, TX
    Home Page:
    Are you asking me or somebody else? As I stated in my post, the cut that I make is a bevel rubbing/gliding cut. It's like cutting with a skew where the cutting edge goes from bevel flat on the wood to a raised position where it begins to cut. As I also stated, it is a completely different presentation of the cutting edge to the wood than the shear scrape where the tool is rolled over to a nearly closed position.
     
  11. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,865
    Location:
    Eugene, OR
    This is 'the name is not correct' for me thing. Two different cuts, and neither one is a scraping cut, since to me a scraping cut is with the cutting edge at 90 degrees to the spin of the wood, or a scraper flat on the tool rest. As soon as the shear angle is changed to 45 or so higher, then it is an entirely different cut, and not a scrape. Don't know what else to call it, and I can't figure out an appropriate name.

    robo hippy
     

Share This Page