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Thread: Negative rake scrapers - any reason to keep a 0 rake angle?

  1. #1
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    Negative rake scrapers - any reason to keep a 0 rake angle?

    I have 2 ‘main’ scrapers that I use; both 0 degree included rake (aka, ground on the front, not ground on the top). I plan on converting one of them to a negative rake so I can use it on the inside of bowls and I got to thinking - can a negative rake scraper do everything that a positive rake angle one can? Should I just plan on converting both of mine (I like to keep one ‘straight-ish’ and the other with a sweeping curve on the left side).

  2. #2
    Join Date
    Feb 2008
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    E TN, near Knoxville
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    12,298
    Quote Originally Posted by Ben Grefe View Post
    I have 2 ‘main’ scrapers that I use; both 0 degree included rake (aka, ground on the front, not ground on the top). I plan on converting one of them to a negative rake so I can use it on the inside of bowls and I got to thinking - can a negative rake scraper do everything that a positive rake angle one can? Should I just plan on converting both of mine (I like to keep one ‘straight-ish’ and the other with a sweeping curve on the left side).
    Me, I keep some conventional scrapers and some negative rake. I'd hesitate to convert all my scrapers into NRS. If I want different NRS profiles I'll acquire another tool or flat stock and grind it as needed.

    A conventional (non NRS) can be very aggressive. This can be very bad when out of control but good when controlled, for example when used for hollowing. Round-nosed conventional scrapers have been used for hogging out material in bowls and such for centuries. Many tools for the inside of hollow forms are actually narrow, flat-topped scrapers held in a stout handle. A similar tip ground with a negative rake would be mostly useless for hollow forms. Flat-topped carbide bits are conventional scrapers. The finish from a conventional scraper will not be anything like that from a better tool such as a sharp gouge but may be fine for roughing out work (especially in green wood) and when followed by a sharp gouge (or a bunch of coarse sandpaper if that's your thing.)

    A NRS is much gentler, not aggressive, difficult (some say impossible) to catch, and can result in a much smoother surface without tearout and such.

    A flat topped scraper may be good for special applications too. For example, I ground one just for forming recesses on face turnings to be held in a chuck. If it had been made with a negative rake it would not work the same and be difficult or nearly impossible to use for this purpose.

    Dovetail_B.jpg

    A box scraper is another example of a scraper that is flat on the top.

    For me, the most useful NRS I've made have a long curve on the side and a short flat or nearly flat on the tip. Also very useful are a variety of smaller scrapers I made - I most often use these on end grain (box lids, etc) but also work well on face work.

    scrapers_neg_rake.jpg scrapers_small_thompson.jpg

  3. #3
    I have yet to do a video on the NRS, but have one 'Scary Scrapers' and another one on shear scrapers. I use scrapers as my primary tool for roughing out bowls. The NRS is fine for very light finish cuts. On bowls, they are best at sweeping across the bottom, but don't leave quite as good of a surface on the bowl walls. The species of wood can make a huge difference. Mostly harder woods will be left with cleaner surfaces, and softer woods will be left not as clean. They do a good job of smoothing out the ripples when your gouge is not working so well.... On boxes, again, standard scrapers and gouges are excellent for roughing, but the NRS excels in fine finish cuts with the end grain. You can get surfaces that don't really need sanding, once you get the hang of it. I NEVER take a standard scraper with a burr to the inside walls of a bowl. The walls can start to vibrate and bowls blow up. I have seen a standard scraper used on a side grain piece of sugar maple, and it left a very clean surface. The burr was honed off, and the touch was VERY gentle.

    If you are using the burr right off of the grinder, that is a very high maintenance cutting edge. If you are using a half round profile, start at the rim, and use the entire edge, the burr is gone by the time you get to the rim of a 12 inch bowl. If you have to push at all, the tool is dull. I always use a burnished burr because it cuts a lot longer, and I feel it is also sharper.

    robo hippy

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