Negative rake scrapers

Re: Negative rake scrapers

Joe Herrmann

>I took a class with Stuart Batty this past summer and he introduced us to the negative rake scraping technique. I don't understand all the "why's" of why it does work, but it does. Stu is having Jerry Glaser make them for him from A-2 steel and is offering them for sale on a limited basis--as a matter of fact, I just bought one from him. Stuart sharpens the tool to a finished edge himself, however.

You could, however, modify one of the 1 1/2" wide scrapers to do the same thing at a fraction of the cost. You grind back the top edge of the scraper and then sharpen from the bottom edge to produce a burr. Just keep in mind that the burr will be gone in a SHORT period of time and it is NOT a tool to use for hogging out massive amounts of material. It is a finishing tool to use for removing tool marks, torn grain, etc.

While a standard scraper has a 7-1 ratio between blade overhang and handle length, these scrapers have a much smaller ratio. In fact, they are not as "catchy" as an ordinary scraper and you don't have to work with the handle elevated above the cutting edge as you do with regular scrapers. You can cut with the handle level.

Stuart is the one who introduced the concept to Cindy and David and it is a technique employed by the ivory turners from years past. It is a remarkable technique that allows Stuart to get his signature bowls so thin.

Re: Negative rake scrapers

Wally Dickerman at Green Valley, Az.

>The negative rake scraper works very well, much like shear scraping. It must have a burr to work, and the burr won't last very long. 15 or 20 seconds at best. You can create this on any scraper that's ground at about 30 degrees (60, depending on which way you measure). Just make a pass at an angle, on the grinder on the back of the scraper, then turn it over and creat a burr.

Wally

Re: Negative rake scrapers

Don Henthorn

>Guess I'm a little dense. No, scratch that; I am a little dense. I can't quite grasp what you are really describing. Can you expand on it in such a way that neophyte can get it?

Re: Negative rake scrapers

Andrew Hilton

>Yep. Beginning (and others too) woodturners have been doing this for a LONG time too. When you take that skew, parting tool or bedan and use it as a scraper, you're basically doing the same thing. Basically, I said.

The idea of "actual" negative rake scrapers is to ride the bevel just as in a gouge but the "flute" of these tools is extremely small.... the height of the burr you raise on the end. With a reduced "flute" size as compared to a gouge, you get only so much bite or cut into the wood at any one time thus reducing (not eliminating!) huge catches. Of course, you only get so much bite or cut into the wood and can't really hog out wood like you can on a gouge either.

So, you can adjust the flute size by simply raising and lowering the burr. Of course, the burr (your cutting edge and resulting flute) doesn't last long at all and has to be refreshed constantly.

So, why does this leave a good surface? I think that we all know that we can get an exceptional surface from a scraper as long as we can control it and have an even burr all around the edge. Well, unlike a regular scraper, you're suppose to be riding that bevel under the raised burr of these negative rake scrapers. This gives you control that you don't normally get with a normal scraper. It's more of a gouge in that regard. Less "catchy" when you have that support under you.

Another reason is the negative rake or the upper bevel on this tool. It allows you to position the cutting end of the tool level or even a little above the handle end while still getting a cutting action on that burr. You can't do that with a normal scraper unless you turn it over on it's side to get a "shear scrape". But then you run into problems of controling that angle and tool position.

Sorby makes negative rake scrapers, btw. Easy to make yourself though. A nice tool for final scraping sometimes but not a must-have in my mind.

Re: Negative rake scrapers

Wally Dickerman at Green Valley, Az.

>Don, You can use a regular skew chisel as a negative rake scraper if it has a burr. Works very well, with a very light touch. Again, the burr won't last long, and it won't work well without it. You can get the same thing with a skew shaped scraper or a round nose scraper, if, after you grind the scraper, you turn it over and grind a tiny bevel on the top, then turn it over again and grind a burr on it. It's used for very light final scraping, and it works. Try it.

Wally

Re: Negative rake scrapers

John Lucas

>Andrew

I think I've seen the Sorby negative angle scrapers and understand how you are saying they work. The Sorby looks like a scraper but has the top 1/3 ground down at about 45 degrees or so to give you the negative rake angle. Is that the tool your talking about.

I'm still confused about the scraper in Joe Herman's photo. It lookes like it has an extreme negative angle and no bevel at all under the cutting edge if I'm reading the photo correctly. That scraper would cut very much like a skew layed on it's side. This cuts wonderfully but dulls the hell out of the skew.

Re: Negative rake scrapers

Andrew Hilton

>Here's a picture of the Sorby negative rake scraper I was talking about. They, at least used to, call it a "Hardwood Scraper" too.

Yeah, I have no idea what Joe showed in his picture. I can't quite make it out.

I'm not crazy about doing that to my skews either. I do most everything with a skew but scraping with it isn't at the top of my list. As you say, dulls it quickly.

Re: Negative rake scrapers

Joe Herrmann

>I apologize for the POOR photo I posted and will try to put up a better one this evening when I get home. It was late and I was in a hurry--not a good combination!

The top of the scraper has been ground away to remove a lot of the metal on the top to produce the round nose shape in the front. There is a tiny bevel formed on the bottom edge that is just enough to raise the burr on the top side. The photo posted in the previous message shows the concept quite well.

Joe

Re: Negative rake scrapers

Mark Kauder, Phenix City, AL

>I too was at the TSS this weekend and saw and handled the scraper that David Nittmann was using. I have photos, but I am not sure they would help. Just imagine a very thick (3/8"-1/2") knife. Curved at the tip, sharpened on both sides, but one side 60 degrees and the other side 40 degrees.

Yes, even Nittmann says that this is only for finishing, must be held level on the rest, and is just like using a skew in the same manner.

Here is a photo of the top.

Mark

Re: Negative rake scrapers

Mark Kauder, Phenix City, AL

>Here is the bottom Photo.

Re: Negative rake scrapers

Mark Kauder, Phenix City, AL

>Side Photo

Re: Negative rake scrapers

Joe Herrmann

>Thanks, Mark. Much better photos than mine and you can see the profile and top view nicely.

Joe

Re: Negative rake scrapers

Don Henthorn

>Thanks Wally, Andy, Mark, et al., I finally got it. Will try that.