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tearout remedy

R

Russ Edwards

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Jan 4, 2009
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I'm turning a large piece of spalted maple. I am having trouble with obtaining a smooth cut without tearout on the portions consisting of end grain. Being spalted maple, the wood is a little pithy. I thought that if I could fill the end grain with something clear like polyurethane, it might support the fibers better. Someone else suggested CA glue. Have any of you have a good solution to the problem?
Thanks,
Russ
 
I agree with Charlie -

I also use a 1 pound cut of blonde shellac to stabilize the wood fibers. I also use shear scraping to try to leave as smooth a surface as possible before sanding. Sharpen your scrapers often....

Rob
 
Russ,

Welcome to the vast world of us bedeviled woodturners. There are as many ways to lessen and get rid of tearout as there are fish in the creek! Everything from super sharp tools, higher speeds, thinned lacquer, thinned white glue, probably thinned (.............) you fill in the blank! It's easier to sharpen your tools first. I'm going to presume that since you're new to turning, you have joined your local club so you can get some hands-on experience to shorten the learning curve. The reason I mention sharpening again and again is that other than the gouges sold by Thompson Lathe Tools (no affiliation, just a happy customer) none of the manufacturers sell you a gouge sharp enough to do a good job, especially with punky wood. So apply a coating of thinned whatever, even floor wax, let it dry, and then take some light cuts with a very sharp gouge, and keep turnin' and learnin'.:p
 
When I get tearout I first start with a sharp gouge. I cut from the rim to the center running the bevel. Then about halfway down I change to a gouge that is ground straight across and has about a 50 degree bevel. If I can't cut it clean still I use a little bit of oil(walnut, linseed, danish, etc.) that usually fixes most of it. Then sandpaper can have the rest.
Wyatt
 
I do one of two things most of the time. First off is to use a very sharp tool and preferably one with a sharper angle. The nose of my Thompson gouge is about 65 degrees but the side wings are sharper, maybe 40. I use a sort of Ellsworth finishing cut with the flute up and the bevel of the wing rubbing the bowl to avoid the catch.
I have an older Sorby bowl gouge that when ground with somewhat of an Ellsworth grind the wings are very sharp, maybe 25 or 30 degrees. This works really well for the above cut. Both of these cuts are somewhat limited(perhaps by my skill) so I can't always cut all portions of the bowl.
In these cases I use a bowl gouge ground in the Stewart BAtty 40 degree grind. In all of these cases it is extremely important not to force the cut. Increasing the speed of the bowl might help or simply reducing the force applied so the gouge travels slower, often work.
If all of that fails and the tearout is minimal I will coat it with Johnson's paste wax and try it again. This often works. If it's really punky wood I use thinned lacquer. It penetrates very deeply which can be really handy. I used to use thin CA and it does work but it's quite expensive.
 
Tool selection and presentation will do more than shellac, or any of the other remedies I've seen and tried. They're at counter-purposes, as you can see. One method - oil - softens the fibers, while the other - resin - stiffens them. If both work, it must be from some third cause.

I use forged pattern gouges for my final paring, using a long bevel by preference because it's easier to stabilize and make slow passage, allowing the wood time to meet and slide the edge, releasing cleanly. If you use a steeper sharpness angle you can still get a good cut, but it's much more difficult to keep it thin with you hand and eye only. If you start to dig, it's all the way. "Shear scraping" presents a steep sharpness angle.

A still of the tool and the presentation. http://i35.photobucket.com/albums/d160/GoodOnesGone/Forged-in-Use.jpg

A video on non-spalted. The centrifugal force is the "riding" force on the bevel. http://s108.photobucket.com/albums/n28/MichaelMouse/?action=view&current=CherryPeelIn.flv
 
I agree that a sharp tool is a MUST, as is the tool presentation.
If you have not seen Bill Grumbine's DVD, "Turned Bowls Made Easy" get it. He covers four different finishing cuts, that I have used to reduce tear-out on spalted Maple (I get lots of this up here in Washington) and not just on bowls. (Thanks Bill, your techniques have saved many a bowl, vase and box! :))
Using these cuts and a good soaking of 1lb cut shellac reduce the tear-out to a reasonable surface, ready for sanding.
Cheers,
 
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