Negative Rake Scraper

[Greg Ketell]

I was asked to post pictures of the scraper I used in making my manzanita bowl.

So here it is. It is just a large bowl scraper from WoodRiver. But I ground a small "negative rake" on the top edge. It is supposed to be roughly 10-15 degrees. This allows the top/cutting edge to be down-sloped like it is supposed to be without having to tilt the whole tool, which is hard inside a bowl. It also lets you "ride the bevel" and still have the cutting edge in a trailing position.

http://sawmillcreek.org/attachment.php?attachmentid=162643&stc=1&d=1285540945

http://sawmillcreek.org/attachment.php?attachmentid=162644&stc=1&d=1285540945

http://sawmillcreek.org/attachment.php?attachmentid=162642&stc=1&d=1285540945

I tried to measure the angle of mine but no joy. Looking at the pictures it seems that my angle is too shallow. But it worked great on my bowl.

http://sawmillcreek.org/showpost.php?p=1521894&postcount=3

I hope this helps someone.

[Marc Himes]

Thanks for the pictures, Greg. I have trouble using a large scraper on my bowls and usually use one 1" or smaller. Having the negative rake grind may be helpful.
Thanks again.

Marc Himes

[Thomas Bennett]

Thanks Greg, that is a nice series of photos. I saved them for the future. I'm looking forward to experimenting with the negative rake.

[David Campbell]

I was asked to post pictures of the scraper I used in making my manzanita bowl.

So here it is. It is just a large bowl scraper from WoodRiver. But I ground a small "negative rake" on the top edge. It is supposed to be roughly 10-15 degrees. This allows the top/cutting edge to be down-sloped like it is supposed to be without having to tilt the whole tool, which is hard inside a bowl. It also lets you "ride the bevel" and still have the cutting edge in a trailing position.

http://sawmillcreek.org/attachment.php?attachmentid=162643&stc=1&d=1285540945

http://sawmillcreek.org/attachment.php?attachmentid=162644&stc=1&d=1285540945

http://sawmillcreek.org/attachment.php?attachmentid=162642&stc=1&d=1285540945

I tried to measure the angle of mine but no joy. Looking at the pictures it seems that my angle is too shallow. But it worked great on my bowl.

http://sawmillcreek.org/showpost.php?p=1521894&postcount=3

I hope this helps someone.

Concerning the scrapers, do you turn the scraper upside down to achieve this negative rake?

[Reed Gray]

Greg,

I don't think you ride or rub the bevel with this tool. If you are doing a scraping cut, then the tool is flat on the tool rest, and the blade is angled down, and handle is high, there is no way the bevel can rub. The negative rake does make a very fine burr which is excellent for very light finish cuts, but not good for roughing cuts, as the burr disappears very fast. I believe that the negative rake makes it very difficult for the tool to catch because of the negative angle.

You could actually rub the bevel if you have the scraper on its edge, at a 45 degree angle, which is used for a finish cut, but as far as I know, I am the only one who uses this cut. I have a specialized tool for this which is swept back like yours, but comes to a point so it more resembles half of a swept back bowl gouge. I don't think this is the cut you are talking about.

I do use 1 3/8 inch scrapers on bowls as a standard roughing tool. It is important to keep the tool rest close to the work as that is a lot of steel to put on the wood at one time, and if you are not ready for it (long strong handle, and tool rest close), or don't have the horse power, it won't work too well. A smaller scraper can be much less 'work' for the turner and lathe.

robo hippy

[Greg Ketell]

Greg,

I don't think you ride or rub the bevel with this tool. If you are doing a scraping cut, then the tool is flat on the tool rest, and the blade is angled down, and handle is high, there is no way the bevel can rub.


That is the point of the negative rake. You can have the tool horizontal and have the cutting edge going downhill rather than having the entire tool going down hill.



The negative rake does make a very fine burr which is excellent for very light finish cuts, but not good for roughing cuts, as the burr disappears very fast. I believe that the negative rake makes it very difficult for the tool to catch because of the negative angle.


If you hold the tool slightly downhill, then yes, the cuttings are very fine indeed. Hold the tool horizontal and it is a bit more aggressive, but you are right it won't be useful for roughing. But I didn't think that was the job of a scraper?



You could actually rub the bevel if you have the scraper on its edge, at a 45 degree angle, which is used for a finish cut, but as far as I know, I am the only one who uses this cut. I learned about that cut in some wood turning video. I've used it once with my small scraper but never with this big one. Too much rotating leverage. And you are right, it made a Wonderful finish.



I have a specialized tool for this which is swept back like yours, but comes to a point so it more resembles half of a swept back bowl gouge. I don't think this is the cut you are talking about. Nope.




I do use 1 3/8 inch scrapers on bowls as a standard roughing tool. It is important to keep the tool rest close to the work as that is a lot of steel to put on the wood at one time, and if you are not ready for it (long strong handle, and tool rest close), or don't have the horse power, it won't work too well. A smaller scraper can be much less 'work' for the turner and lathe.

robo hippyInteresting. Why use a scraper for roughing? Why not a hollowing tool or a big bowl gouge?

[Wally Dickerman]

I got my first real advice on grinding and using a negative rake scraper at a demo by Stuart Batty and by talking to him later. Stuart later wrote an article on the use of the scraper for the AAW Journal.

For best results, the steel used in a neg rake should be harder than the regular M2 HSS, but M2 will work. After talking with Stuart, I ground my NR at about 30 deg. on both bevels. The harder the wood, the better the NR works. It should be used flat on the toolrest and the handle should be level. Only very light finishing cuts should be taken. It's not meant to remove wood, just to smooth it. It must have a good burr. Won't work without it. The burr might last for 15 seconds or so. Then it's back to the grinder. Actually a skew chisel laid flat works as a NR.

I first became convinced of it's value when I was turning a platter from very tight grained quilted maple. Because the grain changes direction constantly with quilt, it tends to chip out even when taking very carefull cuts with a gouge. Using my newly ground NR I carefully removed all of the tiny chip outs and the surface was so smooth that it required very little sanding.

Wally

[Reed Gray]

The shear/finish cuts with a scraper at 45 degrees can be done with the big scrapers, and I do use a round nose scraper. Like you said, with bigger scrapers, the rotational forces could cause problems as in slamming down. To prevent this, always work on the bottom part of the scraper edge, and never above the middle line of the tool. I guess this would translate to don't work with the nose of a round nose scraper, only on the swept back part closest to the tool rest. A burr from the grinder is good for as long as any gouge for roughing, and can give a good finish surface. A scraper with a burnished burr is also great, and gives a slightly finer cut.

As for scrapers being a roughing tool, what is the primary cut you use when you are roughing with a bowl gouge? You have the tool with the flutes on the side. You may have the handle level, or even dropped, but this is a scraping cut. What better tool for a scraping cut than a scraper. Hollowing tools are scrapers, the Oland (3/8 inch HSS bit in a bar, with a scraper bevel on it) tool is a scraper, the Easy Rougher, and other carbide tools with flat cutters (not the ones with the concave discs) are scrapers. I started playing with them some years ago out of curiosity. Scrapers used to be the go to tool for bowls before there were gouges, and I wanted to find out how they worked. They work amazingly well, and for me, they work more efficiently. One added benefit is that when roughing, they throw the shavings up over your hand, not across the top of it like a gouge will. Most people prefer the gouge, but I have had a number of people come up to me after a bowl turning demo and mention that they have to rethink what they know about scrapers.

robo hippy

[Greg Ketell]

The shear/finish cuts with a scraper at 45 degrees can be done with the big scrapers, and I do use a round nose scraper. Like you said, with bigger scrapers, the rotational forces could cause problems as in slamming down. To prevent this, always work on the bottom part of the scraper edge, and never above the middle line of the tool. I guess this would translate to don't work with the nose of a round nose scraper, only on the swept back part closest to the tool rest. A burr from the grinder is good for as long as any gouge for roughing, and can give a good finish surface. A scraper with a burnished burr is also great, and gives a slightly finer cut.


Agree with all the above. Although using the scraper to do the bottom of the bowl prevents using anything but the nose so ...



As for scrapers being a roughing tool, what is the primary cut you use when you are roughing with a bowl gouge? You have the tool with the flutes on the side. You may have the handle level, or even dropped, but this is a scraping cut.
Actually, I only use that cut for "finishing" cuts on the side or exterior. For roughing I use the 45/45/45 cut: tool handle down at 45 degrees, handle trailing the tip so the shaft makes 45 degrees to what you are cutting, flute rolled open 45 degrees. (tool rest adjusted so that in this position the cutting is happening right at center line). Great for hogging out lots of material and yet retains good control.



What better tool for a scraping cut than a scraper. Hollowing tools are scrapers, the Oland (3/8 inch HSS bit in a bar, with a scraper bevel on it) tool is a scraper, the Easy Rougher, and other carbide tools with flat cutters (not the ones with the concave discs) are scrapers. I started playing with them some years ago out of curiosity. Scrapers used to be the go to tool for bowls before there were gouges, and I wanted to find out how they worked. They work amazingly well, and for me, they work more efficiently. One added benefit is that when roughing, they throw the shavings up over your hand, not across the top of it like a gouge will. Most people prefer the gouge, but I have had a number of people come up to me after a bowl turning demo and mention that they have to rethink what they know about scrapers.

robo hippyYup, they definitely have their place. And can be used for lots of things. The bottom of deep bowls aren't one of them without a negative rake (for me).

[Al Wasser]

I'd second what Wally said, of course who can argue with the old wizard. I have seen skews used as an neg rake scraper and I have seen scrapers ground so that about 1/2 of the thickness is ground off on the top. Most things seem to say they work better on dense woods. I've ground a couple of scrapers but I'm still experimenting

[Reed Gray]

Wally, and or any one else, has any one ever experimented with a burnished burr on a negative rake scraper?

robo hippy

[Wally Dickerman]

Wally, and or any one else, has any one ever experimented with a burnished burr on a negative rake scraper?

robo hippy

If anyone is interested, Stuart Batty's article on Neg. rake is in the Spring 2006 issue of American Woodturner. Interesting reading.

Reed, I checked Stuart's article and he says that a ground burr should be used and not one raised by burnishing. He doesn't say why. He recommends harder than M2 steel because the burr will last longer. M4 or A11. The reason a fresh burr is needed is that when the burr is gone the turner needs to press a little harder and the tool will pull out small wood fibers. He grinds the tool at a steep angle. About 50 deg.

Wally

[Kyle Iwamoto]

I bought a burnisher, Kerry tools I believe, although I can't seem to find the page anymore. Works pretty good. Any rod burnisher would work......

[Aaron Wingert]

Negative rake scrapers are really handy for finishing cuts on acrylic as well. I frequently use them on my duck calls and on pens.

[Reed Gray]

I would guess that my curiosity about the burr on a negative rake scraper came from playing with a piece of Mountain Mahogany. I was turning a spindle, on a piece that was maybe 20 degrees off of being straight grain (as in it went side ways rather than straight. One side of the spindle cut clean, the other cut with some tear out. No matter what I did with a skew, or other tools, that was the result. I did try a shear cut with my scraper, and got a slightly smoother cut that way, and about the same cut with a negative rake scraper flat on the tool rest, and the best cut was with a negative rake scraper at a skewed angle. Hmmmmmmm........ may have to experiment some more.

robo hippy

[Leo Van Der Loo]

I used scrapers for many years, as the bowl gouge wasn't invented yet, having found that with a scraper it is hard to get a good surface on softer woods, the harder and denser the wood the easier it is to get an satisfactorily surface with a scraper.

When I got a hold of a bowl gouge I could all of a sudden make smooth cuts on softer wood, no need for expensive or rare tropical wood anymore.

A bowl gouge held in the proper way will cut the wood, not scrape, just like a skew will cut and a rouging spindle gouge will cut so can a bowl gouge cut, and yes you can hold any of those in such a way that they become scrapers, and yes there are conditions where a cutting tool can/will make tearout, just like a plane on flat wood, and the scraper is a way to get around that.

Using only hard dense and wet wood isn't exactly like turning Catalpa or Butternut, Willow or Elm, a good bowl gouge will cut these woods smooth, and a scraper will make a big mess out of it.

Scrapers do have their place, on a bowl bottom, there's no or very little end-grain and the scraper is often easier to use there than a gouge, and with careful use a scraper can take those tool-mark ridges off a bowls wall, but be careful or the surface will deteriorate with the use of a scraper.

Negative scraper works just the same as a tilted-up regular scraper, keeping the angles identical, the wood doesn't care where the rest of the steel goes, it is only the edge that contacts the wood, holding the scraper at an angle the edge will appear to the wood like a more acute edge and will work better.

Though I do agree that a negative scraper is easier to use inside a deeper bowl than trying to hold the regular scraper in a downward position, the scraping is no different than can be had with the same angled regular scraper held in a downward direction.

To clarify my point what changes between a scraper and a negative rake scraper, really, have a look and tell me if anything changes at the point where the tool cuts the wood here's a quick scribbled drawing.

162756

[Reed Gray]

Leo,

Looking at your pics, it took me a few moments to figure out what didn't look right. The standard scraper shown has the tool handle pointing down just slightly. This is normal. The negative rake scraper has the handle pointing up quite a bit. When used, the negative rake scraper is held level, or slightly down like a standard scraper.

I did send an e-mail to Stuart asking about the burnished burr on a negative rake scraper. The bigger the burr, the more it is going to 'pull' on the wood fibers. A burnished burr is a different type of burr than the grinder burr, and can be more aggressive, and does take more time to make. So, a grinder burr is very delicate/small, especially if you just kiss the surface and should 'pull' less. Looks like I have to experiment some more.

robo hippy

[Leo Van Der Loo]

Reed I don't think you get the point, never mind the way the tool happens to appear on this scribble, the important point is the point/ edge where it contacts the wood, the angle is exactly alike between these two tools and the wood, I think you can see that, and that's why I ask what's the difference, to the wood there is no difference, and so the cutting would be exactly the same.

[Reed Gray]

Leo,

I guess there is some thing I am not seeing/understanding here. I guess, to me, the angle the tool is presented to the wood is important, as it can change how the tool cuts. It wouldn't be as drastic as the difference between a shear cut and a scraping cut with a scraper.

Maybe it is the drawings. You have the bottom bevel the same on both scrapers. My bowl scrapers are about 75 or so degrees. My negative rake scraper is about 45 degrees, both top and bottom. It is very similar to a skew chisel here, and I do use a skew as a negative rake scraper for trimming the shoulders of my threaded boxes when I need to remove 1/64th of an inch or less.

Maybe it is the lower drawing of the negative rake scraper presented to the wood. If I tried to cut with a bowl scraper with the tool at that angle, it would almost certainly catch.

It is supposed to be almost impossible to get a negative rake scraper to catch. I figured that was because of the negative angle on top of the scraper has the cutting surface in such a down ward angle, that it will pull out before it catches. Maybe another part of it is because the burr on a negative rake scraper is so minute, that it can't get a big/aggressive enough bite in the wood to catch.

You can rough out with a standard bowl scraper. You can't rough with a negative rake scraper. I have honed the burr off a negative rake scraper, and it won't cut, while if I do that to a regular bowl scraper, it will cut. I am still seeing a difference of some sort here.

Yes, they both cut wood, they are similar tools, but to me, they cut differently.

robo hippy

[Greg Ketell]

Leo,

I guess there is some thing I am not seeing/understanding here. I guess, to me, the angle the tool is presented to the wood is important, as it can change how the tool cuts.

The angle of the "tool" aka the handle and attached tool-steel has ZERO affect on the wood. The only that matters is the angle of the cutting-edge. (If you don't believe this then get a good cut going with your scraper, memorize the angle of the tool-steel/handle, pull the blade out, turn it completely over and put it back in with the tool-steel and handle at the same angle. It won't cut because the cutting-edge is now GONE.) It just so happens that on a "standard" scraper the angle of the tool-steel is the angle of the cutting-edge. But on a negative-rake scraper the angle of the cutting-edge, while related to the tool-steel, is different than the tool-steel.

Think of it this way, if you have a 25-degree negative rake and you hold the tool steel FLAT then the cutting edge is at -25 degrees. If you hold the tool-steel UP at 25 degrees then the cutting edge is FLAT. On a "standard" scraper if you hold the tool-steel flat the cutting edge is flat and if you hold the tool-steel down at 25 degrees then the cutting edge is at -25 degrees.

What Leo's drawing attempts to show is that the top cutting edge of the two tools is the same while the handle position is different. That difference is the angle of the negative-rake.



It is supposed to be almost impossible to get a negative rake scraper to catch. I figured that was because of the negative angle on top of the scraper has the cutting surface in such a down ward angle, that it will pull out before it catches. Maybe another part of it is because the burr on a negative rake scraper is so minute, that it can't get a big/aggressive enough bite in the wood to catch.
The main thing, I think, is that to get a catch you have to have the cutting-edge pointed such that when it snags it gets pulled further into the wood. With a standard scraper this can happen anywhere from angled up, flat, or even just below flat (depending on the angle of the grind and the radius of the bowl). But with a negative rake scraper to get the cutting-edge at the same "snag inducing angle" you have to hold the tool steel pointed way up, which is very unnatural.


You can rough out with a standard bowl scraper. You can't rough with a negative rake scraper. You can, but it takes a long time.


I have honed the burr off a negative rake scraper, and it won't cut, while if I do that to a regular bowl scraper, it will cut. I am still seeing a difference of some sort here.
It's like having the "safety teeth" on your table saw: you can only push in so far before the bottom bevel pulls the cutting edge out. With a standard scraper there is no "safety device" so you can force it into the wood much more aggressively. While this works for some things and some folks, it is much easier to "hurt yourself" with it.

Yes, they both cut wood, they are similar tools, but to me, they cut differently. Very true.

[Reed Gray]

"Kind of like the Jitterbug, it plum evaded me."

robo hippy

[Mark Levitski]

Scrapers for roughing out: whatever removes what wood you don't want left in your piece with the most speed, efficiency, and comfort. I've used a coring system instead of a gouge for that sometimes. I use a big scraper flat on the toolrest too.

I've had my share of tear-out in some woods, and also with catches due to too much edge presented w/ a large scraper. Leo's right, a sharp gouge can be the go-to tool for avoiding some of that. Or, right, a smaller scraper. I get out a detail gouge sometimes to cut a problem area glass smooth. However, I now routinely use the big scraper on the bottoms (read pure "facegrain") of the interiors of my bowls. Zero tear-out, nice finish. The only other tool that works as well is a double-bevel non-fingernail bowl gouge that has an 80 degree bevel with a very short primary face. See Mahoney's signature tools in CSUSA catalog to get some samples of double-beveled gouges.

Anyway, good point about the negative rake to modify the handle position, making it possibly more comfortable and less prone to catching. This is just like the different bevel angles on a bowl gouge that makes it possible to modify the handle position over the lathe. Use a 65 degree to make a rim entry cut and the handle can be way over to the right hand side, requiring a totally different and possibly less comfortable position, especially if you can't slide your headstock. Use the 45 degree and it changes where you stand over your lathe.