Negative rake scrapers

[Reed Gray]

Can some one explain these to me... Yea, I am a scraper psycho, well, with normal scrapers... I use a couple of them, but they puzzle me.

One, what angles? I have one that is symmetrical with about 40 degrees on both sides so I can go either direction. My other one is 70 on the bottom and 20 on the top. I was chatting with Mike Waldt (hope you have seen his videos) and his is some thing like 45 on the bottom, and 30 on the top (have to go check now...). What angles do you use, and why?

I hear the term included angles, which I know means both of the angles, but don't really understand what that does for the tool. It probably has some thing to do with why with a standard grind scraper, no matter how high you raise the handle, it does not cut like a NRS.

With sharpening, maybe it is the CBN wheels, instead of standard wheels, but the burr seems to be fairly long lasting, though not like what I use for bowl roughing. Still playing around with my fine grit CBN wheels on the NRS, and it doesn't seem to make much difference. I have found that I can hand burnish a very fine burr on them as well, and it cuts pretty much the same as the CBN wheel burr, and can be burnished down and then back up a couple of times, like a standard card scraper.

It just doesn't work like I think it should, or I haven't figured it out. I do use it more for end grain turnings as shear scraping seems to cut at least as clean, and cleaner in most cases...

Mike said he didn't know enough about them. I talked to Stuart Batty about doing a video on them, and I could see the idea light turn on in his head, but haven't seen anything yet. I talked to Cindy Drozda about it, and she commented about a couple of people that were better with it than her, but still nothing...

robo hippy

[Bill Boehme]

Reed, I think that there are as many ideas about NRS as there are people who use them. I think that what I use is derived somewhat from Michael Hosaluk taught about a dozen years ago. Basically, my idea is to have a scraper where the included angle is a bit greater than 90° to make it less grabby. Also, I use them only for very fine final scraping to remove a feather thin shaving from the surface. The tool that I use has an angle of about 70° on the bottom side and about 30° on the the top side to give an included angle of 100°. I use a burnishing tool to put a bur on the edge because the bur from the grinder is too fragile. Obviously this tool won't work for anything that is warped because the tool pressure needs to be very light. I don't use it often, but occasionally it comes in handy.

[Fred Belknap]

Reed I am far from an expert on NRS but I do use them. I think my scrapers are around 75 degrees with a very small bevel on top. It seems to keep the scraper from self feeding thus preventing catches. I do mostly natural edge bowls and turn them twice so I don't use them on anything that is out of round. They seem to work better at a slower speed like below 1000 rpm. I have experimented with the pin bevel from Veritas and so far I'm not sure that it is better than the burr directly from the grinder. I have CBN wheels on my grinder, the 80 grit is the one I use on the scrapers. I always use scrapers to clean up both the outside and the inside. Been following your experiment on the finer grit CBN with interest.

[Roger Chandler]

I agree with Fred about the small angle of the top bevel. I have used NRS with about 20 degree on the top and 70 on the bottom...it does reduce the tendency of a scraper to self feed, and of course makes an edge good for shear scraping. I believe numerous combinations will work.

[Dale Bonertz]

Reed,
If you want to understand them contact Tom Wirsing. He is very knowledgeable about them. Not only on how to use them but the best angles, for him anyway, and why. Great guy and demonstrator. If you need his contact info please email me and I will give it to you. I think you still have my private email.

[Grant Wilkinson]

There is a write up online of a Tom Wirsing demo at the Rocky Mountain Woodturners. It says that he grinds his negative rank scrapers with a 20° bevel on both top and bottom, for an included angle of only 40°. For someone as ignorant as me about negative rake scrapers, that seems to be completely different than what most say are the ideal angles.

[Pat Scott]

I tried one angle on top and a different angle on bottom, and found it slow and a pain to adjust the platform twice just to sharpen. Also with a small bevel on top it was hard to see where exactly the edge was contacting the wood.

After taking a Glenn Lucas class I adopted his approach which is 33 degrees on the top and bottom for an included angle of 66 degrees. The bevel is the same length on both sides, so no matter which side you are using you can see the edge. Having the same angle/bevel on both sides lets me use either side as well.

The reason Glenn uses 66 degrees is because his angle gauge has a 66 degree notch and that makes it easy. 35 degrees top and bottom is fine also. I have notes from class that say Tom Wirsing uses 20 degrees top and bottom (40 included), and Kirk DeHeer uses 35 top and bottom (70 included). Stuart Battys Negative Rake scrapers came with a 50 degree included angle "for maximum burr size". The sharper the included angle the bigger the burr, but the more fragile the edge too. I think anything between 50 and 70 degrees included angle is probably fine depending on what you want or the wood. 66-70 degrees is a nice balance between burr size, strength, and longevity. Anything more than 70 degrees is getting too blunt, and requires more force to push the edge into the wood to get it to cut.

I leave my rest set at 33-35 degrees, and as a plus that's the same setting that I use for my skews, beading/parting tool, and I think one more tool I can't think of at the moment. Sure makes things simple and easy.

[Barry Richardson]

I use my wide skew laid on it's side, and it works great to clean stuff up, so I have renamed it my negative rake scraper, since I don't skew much....

[Reed Gray]

Well, I know the NRS is older than Alan Batty after hearing him tell how they made billiard balls out of elephant ivory, a couple of years process and using a NRS to take down the balls a hair at a time, and then let them rest. As for what works best for the included angles, that seems to be about personal taste, kind of like gouge grinds. How fine the burr is, seems to be highly variable. I have used a convex grind skew to adjust the shoulder of threaded boxes to get the grain to line up perfectly, but haven't compared another NRS included angle to compare.... For burnishing a burr, the Lee Valley tool would work on a NRS with a 70 degree bevel, but not on one with 30 or so on each side because it is at the wrong angle.... I may have to contact Tom...

robo hippy

[Roger Chandler]

I have not experimented to the extent some have with negative rake scrapers, but regarding the bevel angles, I do think a number of combinations will work well. I prefer a longer bevel length on the bottom grind and a shorter bevel on the top grind. With this I have not had any problem seeing the cut.....my top bevel is usually no longer than 1/8" to perhaps 3/16ths".

[Reed Gray]

I was able to google Tom, and sent him an e-mail. Not trying to be a commercial here, and this part can be deleted by the moderators if they deem it improper, but with my grinder rest, setting multiple angles is exactly repeatable and easy.

robo hippy

[Dale Bonertz]

I think Tom used to use 20/20 but I think he went to 22.5/22.5. I am not sure why but I am sure he can explain it. He is very knowledgeable with the negative rake.

[Kyle Iwamoto]

For the extremely uneducated people like me, isn't a 20 degree angle more of a skew than a NRS? That's what I use my skews for. (Like Barry) Yes, I do know that scrapers are way thicker than a typical skew.

Actually, I wanted to post this for Robo. How hard is it to modify your Robo Rest to a Tormek. That's what I use. Have a grinder, but none of the One way attachments.... (Continuing the "commercial") I have the grinder rest jig for the Tormek, but it's a PITA to set. NOT repeatable. I like your idea for the Robo Rest......

[Reed Gray]

I have been thinking about trying it. 2 main problems, one is the standard wheels are wider than the opening, and their tool rest bar would be in the way, so I would have to make another bar for the top of the Tormek. I did send a couple to some one who wanted to adapt them to the Tormek. He was going to cut the square tube off, and weld the upright onto the Tormek tool rest. Not sure how that would work though.

robo hippy

[Greg McClurg]

Rudy Lopez has a jig template on his website for his NRS. It is simple to make and works great. His website is rudolphlopez.com.