Negative-Rake Scrapers—Plus or Minus

[Gary Beasley]

I know that this is supposed to be about negative rake scrapers, but since were off on a tangent about identifying trees, I cut down a small tree in the back yard about a week ago that I thought was a Mexican Plum, but I'm not so sure about that now. It has small sharp thorns on the twigs and leaves that sort of look like apricot leaves. The thing that got my interest, however, was that I turned a piece of the trunk which was about 1½" diameter and dripping wet into a small handle that I thought that I might use for a file. I fully expected it to split wide open as the wood dried, but surprisingly it hasn't. It is very smooth and tight grained which has led me to thinking about trying to do some thread chasing.

That reminds me a lot of the description of the hybrid between local pear and bradford pear. Had a funny name, it was said to have spines and was no fun to deal with. This tree is the reason naturalists despise bradford pears so much.

 

[Gary Beasley]

So if I wanted to take a little used scraper and turn it into a negative rake what is the recommended procedure? Ive never had my hands on one to know what its supposed to look like.

 

[Bill Boehme]

So if I wanted to take a little used scraper and turn it into a negative rake what is the recommended procedure? Ive never had my hands on one to know what its supposed to look like.

Grind a 30° bevel on the top and bottom so that you have a 60° included angle. Hone the bevels to remove the grinder burr and then use a burnishing tool (or drill rod or carbide end mill, etc) to raise a small burr. To use the tool, hold it level at centerline and use very light pressure to clean up the surface.

 

[john lucas]

Here is a photo of my negative rake scraper ground from a thompson scraper blank. I intend to run the grind a little ways down the left side but just haven't done it yet.

 

[Emiliano Achaval]

I know that this is supposed to be about negative rake scrapers, but since were off on a tangent about identifying trees, I cut down a small tree in the back yard about a week ago that I thought was a Mexican Plum, but I'm not so sure about that now. It has small sharp thorns on the twigs and leaves that sort of look like apricot leaves. The thing that got my interest, however, was that I turned a piece of the trunk which was about 1½" diameter and dripping wet into a small handle that I thought that I might use for a file. I fully expected it to split wide open as the wood dried, but surprisingly it hasn't. It is very smooth and tight grained which has led me to thinking about trying to do some thread chasing.

Bill, if you successfully chase some good threads I would be interested in trading you for something, a small piece to make a box...

 

[Bill Boehme]

A picture is worth enough words to put you to sleep, so here are a couple pictures that I think helps to show why there is a difference between a standard scraper and a negative rake scraper. Some of the details are exaggerated to help illustrate the difference. In reality, the differences are more subtle.

 

[Glenn Lefley]

I just reground my curved scraper into a nrs 25 deg both sides.

What a difference. No catches super fine shavings if you can call them that. Beautiful finish. On end grain.

 

[Emiliano Achaval]

I just reground my curved scraper into a nrs 25 deg both sides.

What a difference. No catches super fine shavings if you can call them that. Beautiful finish. On end grain.

Welcome to the NRS believers club!! I refused for years, wish I had started using it earlier.... Aloha

 

[robo hippy]

Hmmm. Bill, the burrs you show in your illustrations don't look like what I think they look like, but I don't have any very close up pictures to show that they do look like.... Mostly I never think of them being that vertical, but coming off more at an angle, even if I burnish them. On my 30/30 NRS, if I burnish, I touch the edge, and if I tried to raise it that high, the edge would shatter rather than turn, even with very gentle pressure. For sure I wouldn't want one that vertical for heavy roughing on my bowls with my Big Ugly tools... Don't know for sure though... Trying to figure that one out... Maybe it is due to seeing that illustration, it doesn't 'feel' like they cut the way I think that type of burr would cut.

robo hippy

 

[Bill Boehme]

Hmmm. Bill, the burrs you show in your illustrations don't look like what I think they look like, but I don't have any very close up pictures to show that they do look like.... Mostly I never think of them being that vertical, but coming off more at an angle, even if I burnish them. On my 30/30 NRS, if I burnish, I touch the edge, and if I tried to raise it that high, the edge would shatter rather than turn, even with very gentle pressure. For sure I wouldn't want one that vertical for heavy roughing on my bowls with my Big Ugly tools... Don't know for sure though... Trying to figure that one out... Maybe it is due to seeing that illustration, it doesn't 'feel' like they cut the way I think that type of burr would cut.

robo hippy

They're not vertical, but actually at about the same angle as the steeper burnisher in the Veritas burnishing tool. If you think about it, the Veritas burnishing tool doesn't give you the flexibility to have the burr extend forward further than the slope of the burnishing tool. However, by using a little too much force it certainly is possible to have the burr roll back and curl over ... making it completely useless.

As I mentioned, I exaggerated the size of the burr for illustration purposes to give an idealized depiction of how the burr is contacting the wood. Also, the view on the left side is about 2X normal size and the detail views are about a 25X magnification plus being exaggerated In the real world things aren't so simple. I use a handheld burnishing tool so I have a lot more flexibility in getting the angle of the burr that I want which, like your burrs, wouldn't be quite as vertical I have a better feel for the size of the burr when hand burnishing. Since the burr on the NRS is too small to see, I judge it by feel. The purpose of my post was only to illustrate the difference in angle that the burr contacts the wood for the two scrapers. I wouldn't be able to show that if I only showed the actual size views.

 

[Bill T Tucker]

Bill, thank you for the info on using the Veritas burnisher....wondered why they quit working well, was pushing too hard and when it didn't work well, multiple passes against the angle post. Just used a diamond paddle to clean off old burr and made one light pass on Veritas...worked better. Also sometimes use coarse diamond paddle to raise burr, especially on skews used as NRS, seems to work well. Going back and re-read the whole thread...interesting stuff. Thanks,
bill

 

[Bill Boehme]

Bill, thank you for the info on using the Veritas burnisher....wondered why they quit working well, was pushing too hard and when it didn't work well, multiple passes against the angle post. Just used a diamond paddle to clean off old burr and made one light pass on Veritas...worked better. Also sometimes use coarse diamond paddle to raise burr, especially on skews used as NRS, seems to work well. Going back and re-read the whole thread...interesting stuff. Thanks,
bill

Bill, first of all, welcome to the AAW forum.

You are certainly right about multiple passes being bad. The main problem is that multiple passes can excessively work harden the burr, creating stress cracks, and make it brittle. Additionally, applying too much force or making multiple passes is likely to roll the burr into a curl.

 

[john lucas]

I have found that different steels require different burr raising methods. As Bill mentioned sometimes a course diamond hone works better. Sometimes a medium or fine works better. Sometime steels raise a great burr right off the grinder, others require polishing the old burr off and putting a new one one with one method or another. You simply have to play and see what works for your tool.