New Heavy Duty Bowl Scraper issue with Osage Orange

[Tim Malyszko]

Yesterday, I purchased a new Sorby 1" Extra Heavy Duty Scraper (http://www.woodcraft.com/family.aspx?familyid=5160) and have been having a fit with it on Osage Orange. I used on way back when I took my first turning class and really like it and now that I'm doing more and more turnings, I needed something with a little more heaft than my dinky round nose scraper.

I sharpened it on my wolverine jig and burnished it using my Veritas Scraper Burnisher, just as I do with my other scraper. It's kind of hard for me to describe the issue but here it goes.

When I'm turning a very specific osage orange bowl, I keep running into an issue where the cut becomes too aggressive and it stalls out the motor of my little Jet 1014i or knocks the piece loose from the chuck. I then have to loosen the chuck jaws, re-seat the bowl and start again. Fortunately, it's never bad enough that it throws anything out of balance when I reseat it. I'm using an internal S-shaped tool rest, so I'm plenty close to the bowl walls and bottom. The cut itself looks clean, but it's a very aggressive cut. I've tried moving my tool rest to different heights and introduce the scraper to the wood at different angles and I get one of two results - sawdust or big, thick 1" to 1 1/2" curls. The big curls are what causes the motor to stall out. I've also tried dropping the lathe speed down to 500 RPM and get the same results, just not as often.

I've also tried the same cut on maple and there was absolutely no issue - clean, smooth cuts.

Does anyone have any suggestions on what I may be doing wrong. It's very frustrating because I really want to finish this piece. If I get a moment, I'll try and post pictures of the setup.

Thanks in advance.

[Bernie Weishapl]

Tim it may be the wood. I had the same issue with osage orange and black locust. Cherry, maple, elm, etc. no problem. I think it is the hard dense wood. I moved my rest back and up. Pointed the scraper at a downward angle just about center line. I then turned it to about 45 deg. In other words turned the scraper counter clockwise to 45 deg. That seemed to work the best for me. This has been pretty good for me.

[Paul Heely]

The problem could be that you are raising too much of a burr, especially if you are using a burnishing tool after grinding. After sharpening try removing some of the burr instead of raising it more. I use a diamond hone across the top of my scraper to do this.

[Rob Bourgeois]

Try a negative rake angle on the scraper. Its stops it from catching and is less aggressive while still maintaining a good cut.

Sharpen normally( maybe a bit more like 80degrees or 75 degrees) then grind away the top a wee bit ..say 5 degrees.

Explained here last "question"..
http://www.woodturningdesign.com/askdale/8/8.shtml

Also here last picture...
http://www.bigtreetools.com/articles/sharpening1.html

I learned this from here or some friends I forgot which.

[Christopher K. Hartley]

Tim, I believe Paul is on to something so don't loose sight of it. Since the scraper works OK on other woods and just the Osage Orange is the issue it could also be something I experienced on the same wood but with a different tool. I had a tendency to grip my tool too tight, thus, causing me to to cut too aggressively with the tool. I have been practicing loosening the white knuckle syndrome on all my tools and taking very light cuts (especially true with scrapers) and the problem was solved, at least for me. I also found my bigger scraper was more intolerant of the heavy handed approach than the smaller one. Hope this helps a little. Secondly, I find that my scraper cuts are not as good the lower the speed is. Maybe it's just me.

[Jim Becker]

Are you holding your scraper so that it's presenting with a shear angle or straight on...?? Flat on the tool rest is going to present too many opportunities for a "big bite".

[Curt Fuller]

There's just a lot of surface on a big scraper like that and as it reaches the part of the bowl where it starts to grab I would guess it's matching the curve of the bowl to where it just tries to cut too much wood at one time. Also, you're accustomed to the smaller scraper just bouncing back from the wood. That weight of that heavy scraper holds it's own and just keeps cutting until something has to give. With a small lathe like that you'll need to learn to take just a light shearing cut.

Oh, Osage Orange is about as hard a wood as there is also.

[Tim Malyszko]

Are you holding your scraper so that it's presenting with a shear angle or straight on...?? Flat on the tool rest is going to present too many opportunities for a "big bite".

Right away, I realized presenting it straight on removed too much material, so I rolled it just a bit so that its not sitting flat on the tool rest.

The problem could be that you are raising too much of a burr, especially if you are using a burnishing tool after grinding. After sharpening try removing some of the burr instead of raising it more. I use a diamond hone across the top of my scraper to do this.

I removed the burr and that helped a bit.

After reading some of the posts, I made another attempt and things went a little better until the chuck tenon cracked. Hopefully, I can find a way to salvage the bowl and finish it.

Thanks so much for the valuable information.

[Kevin McPeek]

I'd tend to go with Bob on this one and try a negative rake scraper. It will dull very quickly though. I have my cheapo HF tool that I made NR scraper and it works well when a normal scraper starts to self feed as the big ones tend to do on dense wood. The steel is less than ideal and when I am using it I leave the grinder running because it dulls so quickly.
Here is a pic of one http://www.turnwood.net/Photopost/sh....php/photo/855 I radius the tip on mine.
As a test you could raise a burr on one side of a radiused skew and give it a go. The angles are off and you won't want to overhang the tool rest much but being careful and only engaging a small part of the tool you should get an idea if it will work. I know it's not the best practice but it's just a test.

[Bill Hunt]

Hi folks, normally I do more lurking than talking but I'll just add that with a scraper you need to let the wood come to the scraper instead of the scraper coming to the wood. I also like to hone the back of my scrapers, it's not nearly as agressive but still gives an excellent cut/scrape?
Bill Hunt

[Jim Underwood]

Seems like there was an article on negative rake scrapers in one of the AAW journals in the last two years. The turner had trouble turning really thin and deep hollow forms in the harder Australian woods, and so tried the negative rake scraper which solved all his vibration and tearout problems.

[Allen Neighbors]

I don't raise a burr on my scrapers, other than what is left by the grinder.

Just posted this on another forum with some minor changes:
When I have my cutting edge too low, I get catches. Now lets all look at this problem from a different perspective. Think about this deal from the standpoint of the center of a bowl (but don't try to stand there), and as if the wood is going around in a circle (Well, it is!), and as if you are going to do all your work in the upper left quadrant... from 9 to 12 o'clock.
Now, draw an imaginary verticle line through the center of the bowl, top to bottom as you look at it from the tailstock end. As the wood circles over the top of the arc, it's moving away from the verticle position, and arcing downward. When it passes the 9'oclock position, it heads back toward the verticle position. Make sense?
If you will turn the flat on your scraper to a 45 degree angle... like this slant mark / with a little more lean to it, and take very light cuts using the lowest edge of the cutter (like cutting on the lower edge of a skew), cutting only in the upper left quadrant of the piece, the wood is moving away from the cutter, which will make the cutter "shave" the wood. I also use a speed as fast as I can safely get it... probably around 14-1600 rpm, and take light cuts with a relaxed grip.
If you have the cutter below center (anywhere between 6 and 9'oclock), the wood is moving toward the vertical position and the cutter, which will make the cutter dig into the wood (catch).
When you go "around the corner" (transition from bottom of bowl to side of bowl) you want to rotate the scraper just slightly back toward a horizontal position (slightly less than the 45 degree slant / ), and keep cutting on the lower edge of the slant as you move up toward the top of the bowl, but remove the scraper from the wood, before you get to the rim.
Now this all makes sense to me, cause I do it this way all the time. But, judging from my inability to explain the theory of relativity and nuclear fission, I'll bet it's confusing as heck to the rest of you. Right?
Well, anyhow, it works for me. Al