robo_hippy
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Each tool can be used to make basic cuts, which are pretty much bevel rubbing cuts, scraping cuts, and shear scraping cuts. These are pretty much describing how the cutting edge is presented to the wood.
So, bevel rubbing cut, mostly used with bowl gouges and skews, the bevel very gently rubs the wood as the edge cuts. Most of the time, the cutting edge is at a shear angle to the rotation of the wood. A peeling cut with the skew is similar, but is more square to the wood. Note here, skews, gouges, and scrapers can all be used with a bevel rubbing cut.
A scraping cut is with the cutting edge at 90 degrees to the spin/rotation of the wood, which also is a cut with 0 degrees of shear angle. Most common is a scraper flat on the tool rest. A skew chisel is a negative rake scraper and can be used this way. A gouge, held level, with the flutes rolled all the way over on the side is also a scraping cut.
A shear scrape is another cut that really is not a scraping cut. I will be doing a video on just shear scraping.... Anyway, the shear/sheer (according to Lyle Jamieson) is with the cutting edge at an angle to the spin/rotation of the wood and the bevel is not rubbing. So the cut isn't really a scraping cut at all because the cutting edge is at an angle to the spin. I don't think the name we have given this cut applies correctly, but can't think of another name for it. The idea behind this cut is for clean up of tool marks and some tear out. The higher the shear angle is, the cleaner the cut, so most of the time this is in the 60 to 80 degree range vertical. Mike Mahoney just did an article in the AAW magazine about it and there is a video link to it. Most use gouges for this cut, but I prefer scrapers. The idea with the high angle is kind of like speed bumps on the road. Hit them square on (like a scraping cut) and you get a pretty big bump. Hit them at a 45 degree angle, and the bump is still there, but it is smoother to go over. A 70 degree angle makes the bump almost disappear. So, a high shear angle does a better job of gently lifting the fiber as you cut so you get less tear out. Also, since you are not rubbing the bevel, it does a great job of getting rid of the little bump that is in every bowl (from cutting uphill/downhill/uphill/downhill on every rotation) so you can get it pretty much perfectly true. On the outside of a bowl, you drop the handle to get the high shear angle. On the inside of a bowl, you can't drop the handle much because you run into the banjo, or the bowl rim, or the lathe. This is where I use a ) profiled nose shape on my scraper. With that nose shape, you have to drop the handle a bit and work on the lower half of the tool edge because if you try to work on the high side, the tool is not balanced, and that edge will catch. If you have ever used a skew, this is a mistake we all have made, several times. I have seen a couple of well known turners who when using a scraper to shear scrape the inside of the bowl keep the handle high because "Well, I am using a scraper." "Yea, but you are not doing a scraping cut....". On one of my videos where I am using scrapers, with the big ugly tool (not the ones on the Big Ugly tool), where I am shear scraping the rim, and as I come from the inside rim to the outside of the rim, I get high sided..... Nice catch!
I do have a video 'robo hippy turns a bowl using just scrapers' in the video section here, or up on You Tube. Along with many others dedicated mostly to bowl turning.
Hope this explains things better....
robo hippy
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