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Negative Rake Scrapers

Jamie Straw said:
In one of our recent demos, the member made note of the fact that he used the Ellsworth grind for most of his turning. Sure would simplify things. Where do I sign up?🙄
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Lots of folks teach using the Ellsworth Grind or something that has evolved slightly from it.
A three day class with Trent Bosch In Fort Collins would change your woodturning life.
Lyle Jamieson was totally Ellsworth when I met him. He has made some modifications but...

Get that member to help,you....

The Michelson grind is another great do most everything grind.

With an Ellsworth ground gouge and a spindle gouge I can turn any convex open form.
 
Very interesting thread. I have been experimenting with NRS for a year or so. I sell to state run reseller and they request the NE type bowls similar to my avatar. The NRS works great for doing the wings on this type turning. My procedure is to use a gauge to cut to the thickness I want then finish with different NRS. My first cut is with a gauge inside down till I am in solid wood, then I use a Sorby scraper .75" x.5 ground to 75 degrees on the bottom and a small 15 degree on the top. The extra thickness of the half inch tool seems to dampen the vibration that one usually gets on this part of a bowl. If I lost all my scrapers the half inch scraper is the first one that I would replace. My process is to rough out green wood and let it dry before finish turning. NRS have saved me a lot of work sanding, reducing it by at least half.
 
If a NRS has the same angle between the bevel and intersecting top surface as a traditional scraper, and the forming of the bur is the same for both, wouldn't the capability of both be the same?

If the scraper is held flat to the tool rest, wouldn't it be the same as tipping one to match the presentation of the other?

If the discussion is about shear scraping, wouldn't the result also be the same if the presentation of the cutting edge was the same for both?

For me, it's been quite a while since I did some limited experimenting, and concluded that a NRS has no advantage over a standard scraper, but I'd like to hear some discussion from those who disagree with my conclusions.......

ko
 
Not only that, Odie, it makes a difference where, inside the curvature, you place the flat supported tool. Same grind above center, much different angle than if used below.
Back to the edge versus wood article. http://homepages.sover.net/~nichael/nlc-wood/chapters/caop.html

"In furniture hardwoods, grain reversal is much more common than in sofwood; indeed, some of the attractive grain patterns are a result of this. Some even have "roey" grain -- in which the grain direction changes repeatedly across the width of the board, even within the width of the plane blade.

In dealing with this, final finish is done with a hand scraper or a scraper plane, with a nearly vertical blade. Why is this effective? A vertical blade has little tendency to cause splitting or fiber separation ahead of the edge. The action is not to lift the shaving, but to crush the wood cells, decrease their strength, and scrape them away in very thin shavings. Much more work must be done to remove a given quantity of wood, but a smoother surface is gained."

Sounds a lot like what happens as we go 'round and 'round in a bowl.


 
I am still working on figuring them out. There seems to be two styles, one like the skew with the same bevel on each side, in the 30 or so degree range, and the other is more like the 70/20 bevels. They do cuts that I can not do with a standard scraper, no matter how high or low the handle is held. I was talking with Stuart Batty at the Symposium about them and he says that the standard scraper cuts differently than a NRS because the top surface of the tool, where the burr is formed, is parallel to the bottom surface. Makes no sense to me because the only surfaces that matter to me are the two that join where the burr is formed. He didn't explain, I guess because it is obvious to him, though not to me. He also claims that a NRS cuts the same as a shear scrape, which I don't agree with at all. A NRS flat on the tool rest is still a scraping cut with the cutting edge at 90 degrees to the rotation of the wood, and it does pull more than an angled cut, which is what a shear scrape is, and most of the time I can get a cut that is as clean or cleaner with a shear scrape, which slices more than pulls. However, the NRS does wonders for small tool marks that I can sand out, but couldn't take out with a standard scraper. Biggest problem with using them is that they really go dull quickly, and I keep trying to cut some more. You can still feel the burr, but it doesn't cut as cleanly. I can use the same grit wheel to form the burr on all 3 variations of scrapers (standard, 30/30, and 70/20), and the standard scraper cuts far longer than any of the NRS's. Doesn't make any difference in how hard I push the tool into the grinding wheel....... Haven't figured it out yet...

robo hippy
 
hockenbery said:
Fred,
Gorgeous bowl. Curious as to why you turn twice? It works?
Al
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I have been ask this several times. It's mostly the way l like to do them, I don't have problem with the edges warping a bit but the rocking chair bottoms I don't like. I have done several from green to finish, just didn't like them as well as twice turned. I do end grain NE to green to finish but I usually go back and finish the bottoms after they dry, sometimes patching the cracks.
 
odie said:
If a NRS has the same angle between the bevel and intersecting top surface as a traditional scraper, and the forming of the bur is the same for both, wouldn't the capability of both be the same?

If the scraper is held flat to the tool rest, wouldn't it be the same as tipping one to match the presentation of the other?

If the discussion is about shear scraping, wouldn't the result also be the same if the presentation of the cutting edge was the same for both?

For me, it's been quite a while since I did some limited experimenting, and concluded that a NRS has no advantage over a standard scraper, but I'd like to hear some discussion from those who disagree with my conclusions.......

ko
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Yes, sort of. But lets say the angles are 45 degrees, you would have to tip a flat surface scraper at 45 degrees down to achieve the same effect. You would have to have the tool rest up real high to cut at center, and I don't think it would be real save.
And you could use a traditional scraper in the same manner as an NRS, but again it is going to need an awkward angle to replicate.
The NRS is a great tool for very fine cuts. The edge doesn't last but about 15 seconds on a real hard wood so it doesnt work well for alot of reshaping or massive amounts of wood removal. You can remove alot more wood with a standard scraper. But a standard scraper has a steeper learning cure as it is difficult to get a catch on an NRS

I have rounded face NRS' but rarely use them on the insides of a form.
 
robo hippy said:
I was talking with Stuart Batty at the Symposium about them and he says that the standard scraper cuts differently than a NRS because the top surface of the tool, where the burr is formed, is parallel to the bottom surface. Makes no sense to me because the only surfaces that matter to me are the two that join where the burr is formed.
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That was the answer. On a standard scraper, your cutting edge is parallel to the bottom cutting edge. On a NRS, there is a bevel top and bottom, so the edge at the tip is not parallel to the bottom.
 
robo hippy said:
I am still working on figuring them out. There seems to be two styles, one like the skew with the same bevel on each side, in the 30 or so degree range, and the other is more like the 70/20 bevels. They do cuts that I can not do with a standard scraper, no matter how high or low the handle is held. I was talking with Stuart Batty at the Symposium about them and he says that the standard scraper cuts differently than a NRS because the top surface of the tool, where the burr is formed, is parallel to the bottom surface. Makes no sense to me because the only surfaces that matter to me are the two that join where the burr is formed. He didn't explain, I guess because it is obvious to him, though not to me. He also claims that a NRS cuts the same as a shear scrape, which I don't agree with at all. A NRS flat on the tool rest is still a scraping cut with the cutting edge at 90 degrees to the rotation of the wood, and it does pull more than an angled cut, which is what a shear scrape is, and most of the time I can get a cut that is as clean or cleaner with a shear scrape, which slices more than pulls. However, the NRS does wonders for small tool marks that I can sand out, but couldn't take out with a standard scraper. Biggest problem with using them is that they really go dull quickly, and I keep trying to cut some more. You can still feel the burr, but it doesn't cut as cleanly. I can use the same grit wheel to form the burr on all 3 variations of scrapers (standard, 30/30, and 70/20), and the standard scraper cuts far longer than any of the NRS's. Doesn't make any difference in how hard I push the tool into the grinding wheel....... Haven't figured it out yet...

robo hippy
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Maybe Batty was considering if the presentation angle of the tool shaft itself were the same, then it would make sense that the actual presentation of the cutting edge would be slightly different......?

From my perspective, my methods of raising a bur have changed considerably beginning a couple years ago.....and, I'm still observing and modifying this. One thing that is unquestionable IMHO, is that raised burs are a great improvement over ground burs, but for the very final finishing cuts only. Standard ground scrapers do not exceed the ability of raised burs......with the exception of the very final finishing cuts. The raised bur takes some effort to create, and it doesn't last very long......but, it's capable of the finest cuts of any scraper that I've had any experience with.

Because of these recent changes in how my scraper burs are created, I think it's probably a good idea to test the NRS again, but using a raised bur.......

ko
 
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Question: When using a NRS in the shear cut mode, does the top bevel ever come in contact with the wood being cut?....sort of like a bevel rubbing cut with a gouge?
 
odie said:
Question: When using a NRS in the shear cut mode, does the top bevel ever come in contact with the wood being cut?....sort of like a bevel rubbing cut with a gouge
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I have only used it as a scraping tool flat on the tool rest handle level.
If used at an angle It could work as a shear scrape if you pull it with the lower bevel nearly perpendicular to the wood's surface.

Avoid riding either bevel and pushing like a gouge - potential for a massive catch !

Negative rake is used flat with tool rest set so that the bevel cannot contact the wood ( center on a flat surface, above center inside a bowl, below center outside a bowl)

Al
 
odie said:
Question: When using a NRS in the shear cut mode, does the top bevel ever come in contact with the wood being cut?....sort of like a bevel rubbing cut with a gouge?
Click to expand...
No, the cutting edge is perpendicular to the work. If can be a bit daunting because in this fashion, you would typically cut about in the middle of the scraper, because if you catch the top edge it is extremely unforgiving. I will do it occasionally on the exterior of a bowl when nothing else seems to be working, usually with a soft wood like silver leaf maple or box elder
 
If you have a NRS in shear scrape mode and rub the bevel, it becomes a skew chisel. Not advisable on bowls. When using a scraper for shear scraping, I always work on the lower half, of the tool, and avoid center or above. Nasty catches, similar to what happens if you use the upper half of a skew chisel. The tool is not balanced, and the part that is cutting is not directly over the anchor point on the tool rest. Big nasty catch. My preference for shear scraper on inside has a ) shaped nose. Lower the handle a bit and you can not get over center. I do some times use a round nose scraper, but it just doesn't feel right. I have used swept back scrapers/inside scrapers for this cut, and they just don't feel right either. Just about any scraper on the outside, handle low.

'Included angles' are mentioned by Stuart, which means the top and bottom angles. With a standard scraper, I figure the bevel is 70 on mine, so the top would be at 0 or 90. Just can't see how the bottom being parallel figures into the factor.

Burrs have changed a lot since the CBN wheels have come onto the market. I have 80, 180, 600, and 1000 grit wheels. For standard scrapers, the burr from the 80 and 180 are both excellent for heavy roughing cuts on bowls, and do a good job on shear scraping. The 600 and 1000 grit wheels leave a delicate burr that is lousy for heavy roughing as it gets dull quickly, but produces an excellent burr for very fine finish surfaces. I haven't found that a burnished burr has any advantage over the CBN wheel burrs. I do hand burnish and don't have the bench top mount from Lee Valley, or a carbide hand burnishing rod, so can't really compare them. On the NRS it doesn't seem to make any difference which wheel I use, the burr cuts pretty much the same. It is the same with a burnished burr also, and I have tried to keep it very light on the burnishing the skew chisel type because little pressure on the fine bevel angle would curl it too far over. This seems to be more true on the skew like NRS, and almost the same on the 70/20 NRS. It has been so long since I have used standard grinding wheels, I can't really remember the burr they left, but do remember liking the ones off the CBN wheels on first try. With the fine grit wheels, you are at least honing the burr, and I think there is a little burnishing going on, kind of like fine abrasives on wood that polish the scratches out rather than cut and shape. Need micro photography for that...

No matter how high I raise the handle on a standard scraper, it will not cut like a NRS.

I have wondered about the comments from turners, Stuart among them, who say that scrapers are 'self feeding' and like to dig in because of the burr, and this is what makes them more catchy and grabby. The more I use them, the more I feel that this is not accurate. I think it is more due to the large surface area, and if you don't really understand the tool, you will end up getting too much cutting edge into the wood at one time than is safe, and you get over powered. With the coming of the carbide tipped tools, and their popularity, I think most of that is because the cutting edge is a lot smaller than standard scrapers, and that is why they are easier to control, so people like them more, and find them easier to use.

I some times use bevel rubbing cuts with my scrapers. I have tried it with the 70/20 type NRS, and didn't find it did anything much worth trying again.

The mystery remains....

robo hippy
 
robo hippy said:
My preference for shear scraper on inside has a ) shaped nose. Lower the handle a bit and you can not get over center. I do some times use a round nose scraper, but it just doesn't feel right.
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Help me understand, please...what's the difference between a ) shaped nose and a round nose?

robo hippy said:
I have wondered about the comments from turners, Stuart among them, who say that scrapers are 'self feeding' and like to dig in because of the burr, and this is what makes them more catchy and grabby.
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I have read that an off-the-grinder burr can be more aggressive and catchy than a burnish-burr. A couple of weeks ago, having forgotten that, I took my regular scraper (not NRS) straight from the grinder to the bowl. OOPS! got my first-ever scraper catch. Might not have been solely from the burr, but I'm pretty sure that contributed. You're such an expert with the scraper, Reed, bad stuff just doesn't happen to you!😉

robo hippy said:
The mystery remains....
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And isn't it fun?!?
 
Round nose is a half round profile, ) nose is much more broad so you don't have to drop the handle nearly as much to stay on the lower half. It is the same profile I use on my BOB (bottom of bowl) gouges which also makes it easier to get more vertical for a higher shear angle.

Bad stuff doesn't happen to me???? Not a single mistake that I haven't made, and most of them a couple of times. Launched one in my using the Big Ugly video clip, good thing I have my camera man trained to stand out of the line of fire....

robo hippy
 
NRS is very confusing. I have seen several sites recommending a 90 degree included angle and presenting the tool with the handle down to ride on the lower bevel and then raise the handle until the burr starts to cut. That includes the Robert Sorby site.
 
Roy Ward said:
NRS is very confusing. I have seen several sites recommending a 90 degree included angle and presenting the tool with the handle down to ride on the lower bevel and then raise the handle until the burr starts to cut. That includes the Robert Sorby site.
Click to expand...

I'd suggest watching the Raffan video on the AAW site.
 
Well I agree with a lot of what's been said. On my thick scrapers I also do a 3rd bevel to speed up sharpening and establishing the burr. I don't do this on the scrapers that I sharpen like Stewart Batty where you flip the tool each time you sharpen. That has advantages and disadvantages. On my flat scrapers it's wonderful. Just flip the tool hit the grinder and back to work. On my round scrapers it works the same but I like to sweep the grind around the side a little for doing box interiors. If you do the Stewart Batty flip technique you then have to do this swept back grind on both sides, not just the left like you would for a tool that has 2 different bevels.
When I did my square box ornaments I had to turn 6 small bowls in each one and I played with 3 tools. I regular scraper, a negative rake and a Hunter Ornament hollowing tool. The regular scraper tended to be a little grabby unless you were really careful. The negative rake was very controllable and easy to use and left a nice finish. It was also easy to use in the areas where there were 3 holes and you were cutting air. The Hunter tool was very fast at hollowing and left a suburb finish but took a lot of skill to get a perfectly smooth shape. I also took skill to not let it dip into those holes when turning past them. so what I ended up doing is cutting as much as I could with the Hunter and if I did it perfectly I left it because it didn't need sanding. If it had tool marks from less than perfect control I used the negative rake scraper to clean them up. It was really a good learning experience going back and forth between the 3 tools.
 
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