Negative Rake Scraper

The cutting edge on a Negative Rake Scraper (also known as an NRS) is formed by one step on the grinder. The grinding action forms the hook.

The key with a Negative Rake Scraper is that the α angle must be less than 90º. If not, it won't work.

There seem to be two schools of thought on the shape of the cutting edge for this tool, and both options are shown below.

Option 1

This approach is one that is easiest to maintain, especially when scraping really oily woods.

Option 2

This tool is relatively new to the scene, so to call this the "old school" approach seems odd, but let's go with that for now.



General Guidelines
Cutting Edge α βTop βBottom Comments
Option 1 45º 22.5º 22.5º Every time you resharpen, re-grind both sides of this scraper. This will clean off the residue left on the top edge by the scraping process (especially when scraping oily woods).

Making the top and bottom angles the same makes this significantly easier as you can sharpen the top, flip the tool, and then sharpen the bottom.

On the Tormek, sharpen with the SVD-110 attached to the support bar in the vertical position (with the grinding direction being towards the edge of the tool). This does two things :

  1. it makes raising the burr faster and easier, and
  2. makes sharpening easier as the tool is being pushed into the tool rest, not being pulled away from it. (My experience when trying this from the other position was that the tool was being constantly pulled away from the tool rest and holding it there was difficult.)

This is my preferred approach.

Option 2 65º 15º 50º Grind the top first, and make it about 3mm (3/16 inches) wide. Then, you resharpen by only re-grinding the bottom. Once the top gets down to 1mm or so, you will need to re-grind it again.

An advantage to this approach is that you only need to sharpen one side at a time, so it is faster to resharpen (by a few seconds or so). This can add up as scrapers must be resharpened very often.

Various people recommend different angles for α, but the ranges are typically in the 50º - 75º range.



Notes & Comments
Information regarding Grindstones




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