Scraping and shear scraping are supposed to be simple, but I expect we've all had little mishaps with them on occasion. That‟s certainly no fun. It‟s supposed to be safe and easy. What goes wrong? As a beginner, I used a scraper more than I should have, while learning the proper use of cutting tools. There was a time when I had more trouble with the scraper than I did with a gouge on the inside of bowls. I was getting afraid to touch the wood. What was that all about? Needless to say, it had to do with things like the overhang off the tool rest, the thickness of the scraper, and the warping of the wet wood as stresses were relieved, but it also had to do with the height of my tool rest. And that's where the safety and confidence come in. I was reminded of this while I was watching the John Jordan hollowing tape from our Library (reviewed below). As he was working, he made some simple observations that are critical; I will repeat them here.
1. He was using a round-nose scraper flat on the tool rest on the outside of a large, deep cove that formed the neck of his large, end-grain vessel. He expressed the thought that it would be a shame to lose all the hard work he had put in at this late time and pointedly moved the tool rest lower. He said, in effect, “You can't get a catch scraping on the outside of a work piece if the tool is level and you are cutting below center.” That's a pretty straightforward observation, but a very important one. If the tool is below center and it starts to grab, it can‟t feed into the wood because as it gets pulled lower, it swings into air, not wood. Maybe you get a warning sound, but not a catch that rips the piece out of the chuck and smashes it into pieces. So be safe and confident and make sure you‟re scraping below center on the outside of a piece. The opposite is true on the inside – you have to be above center, for the same reason – you want the tool to swing into air, not wood, if it starts to grab. This is particularly true for blind hollowing! (Further, as you read above, Stuart Batty believes that only a negative-rake scraper should be used down the inside wall of a bowl where it contacts end grain.)
2. John was doing a delicate shear scrape on the outside of the vessel with a diagonal scraper, with the tool at a very high axial rotation angle off the tool rest, and I was watching his contact point very carefully and thinking about what might happen if it got too far up toward the long point. As if reading my mind, he made the observation that in order to avoid a dig in, he was using a pull cut with the handle leading. He pointed out that if he got the tool perpendicular to the wood or actually started a push cut, he could get a catch. I've occasionally had some bad sounds come from my shear scraper and didn't understand the problem -- now I know why. Per above, it is also important to work below center on the outside.
OK, now here's the “don't do this at home” part. He was so confident in the safety of his shear scrape that he actually used his finger as a guide under the tool. Now you're not going to see me putting my finger between the tool and the rest, but his point was well made. As a related aside, some turners have been known to use cabinet scrapers on the outside of vessels with no tool rest at all. As long as you work down low and pull gently across the convex surface, it's little different from sanding. [I guess I shouldn't be promoting things like that in a “Safety” article. You didn‟t hear this from me! Have an experienced turner show you how to do this before you try it on your own.] |