Scrapers for Woodturners, Part II: Negative Rake ScrapersComments (0)
For about a year I’ve been experimenting with making negative rake scrapers. The main difference from a regular scraper is the addition of a top bevel. Usually the bottom bevel is steeper than the top, but sometimes the top and bottom bevels are the same. Negative rake scrapers also don’t hold their burr as long, so they are not well suited for hogging out material, but they do a very good job at smoothing the surface of a turning. Several well-known turners have done experiments and found the steeper the bottom bevel the bigger the burr, and the longer it lasts.
Another important distinction is the angle of attack– negative rake scrapers are held flat and level on the tool rest, cutting at the center-line of the work. This arrangement makes it very easy to control and also lessens the chance of a catch. They still require some practice to use effectively as slightly lowering or raising the handle will result in the tool not cutting properly or at all.
The author's custom negative rake scraper
The big question of course is what’s the best bevel combination for a negative rake scraper? There is an old saying that if ten turners are asked for an opinion, eleven answers will be given, and it definitely applies to this question. The real answer is certain combinations work better for certain turners and certain situations, or in other words, try something until it works. I’ve found from watching others who use negative rakes, and from my own experience, a bottom bevel between 40 and 60 degrees and a top bevel between 15 and 25 degrees works well. I’ve also found different bevel combinations work for different types of turnings and woods, so I have multiple scrapers in my tool set.
Once the bevels have been set, it’s time to raise the burr. The bottom bevel is burnished in order to raise the burr on the top edge where the bevels intersect. The process is very similar to the one for single bevel scrapers– burnishing can be done with a burnishing tool, diamond hone, or even sandpaper on a flat surface. If done properly, the burr should be able to be felt by dragging a fingernail down the top bevel to the tip. When using a scraper with the same top and bottom bevels, be sure to mark which side is up (and therefore where the burr is located). If the scraper is mistakenly used upside down, it will not cut anything and be quite frustrating.
I’ve found I can raise the burr on my negative rakes several times before I run the burnisher over the top bevel to remove any old pieces of burr, and then I raise a new one. The entire process really started going quickly once I got the hang of it. So grab an old scraper, convert it to a negative rake, and start experimenting!
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