Turning Archive 2006

Subject:
Negative Rake Scraper.....

Wally Dickerman in Arizona
>A couple of years ago a friend told me about the negative rake scraper, and how well it worked under certain conditions. A negative rake scraper is ground on both sides, similar to the way a skew is ground. I happened to have a heavy duty 1-inch, square nosed tool. I ground away one side of the cutting edge a bit and tried it. I wasn't impressed with the results, so I put it on the tool rack and forgot it.

At the recent Phoenix symposium, I watched a demo by Suart Batty on the negative rake scraper, and later I read the article by Stuart in the American Woodturner. He emphasized that the burr must be substantial. I decide to get out my NR scraper and give it another try. This time I re-ground the cutting angle to a steeper 45 degrees, and instead of grinding it on my 60 grit wheel, I ground it on my 1-inch belt sander using a 60 grit belt. This gave a much heavier burr.

I mounted a dry, rough-turned piece of quilted maple on the lathe. In my experience, quilted maple is just about impossible to turn without having areas of rough surface, due to the fact that the grain is constantly changing.

After doing the best I could with the bowl gouge, I carefully shear-scraped the piece. There were still several rough areas that would require a lot of sanding. I then tried the NR scraper, using a very light touch. It produced very light, feathery shavings. I had to touch up the grind a few times, as the burr disapeared in about 10 seconds. In a few minutes the rough areas had disappeared, and the surface was very smooth.

Needless to say, I am very impressed with the performance of this tool. According to Stuart, the harder and denser the wood, the better it works. He says that it won't do well on soft and spalted wood. The tool works best when held level. When the burr is gone it doesn't work at all. Because of the way it's ground it's not nearly as aggressive as a scraper that's ground the regular way. It's not used for removing wood, just used with a light touch for smoothing the surface before sanding. Sanding is much easier after using this tool.

Wally

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