cottonwood, grrrrrr

[Bob Strand]

Having fits with tear-out on cottonwood. Its dry, not big, 10" or so in diameter, and I can't seem to get a clean cut. Tools are sharp, trying not to use too much pressure but I'm always getting some degree of pitted tear-out on either side of my bowls. Any comments?

 

[hockenbery]

Having fits with tear-out on cottonwood. Its dry, not big, 10" or so in diameter, and I can't seem to get a clean cut. Tools are sharp, trying not to use too much pressure but I'm always getting some degree of pitted tear-out on either side of my bowls. Any comments?

Soft woods are a challenge and dry softwoods can be even more prone to tear out than wet softwoods.

I can't see what tool you are using or how it is presented. I can give a few general,suggestions

Cutting tools will out perform scrapers for clean cuts on soft woods ( on really dens woods scraper can out perform cutting tools)
Riding the bevel gives a cleaner cut.
Sharper tools give cleaner cuts.
Cutting down hill on the grain gives cleaner cuts because each fiber being cut has a longer one underneath supporting the cut.

When I work with punky wood it is prone to tear out because there is little or nothing holding the fibers to each other so all the fibers can bend and be pulled out.
Softer woods are much the same. The fiber want to pull instead of cut.

I go through a bag of trick to get a clean cut.
Try a pull cut with the Ellsworth grind instead of a push cut ( the wing is sharper than the nose has a bevel angle about 25 degrees)
Try a 1/4" going instead of a 1/2" gouge ( smaller tool get sharper)
If I can use it safely I may try a 3/8" spindle gouge ( spindle gouge with a 30 degree bevel

I wet the area with water. The fibers swell and stiffen.
I apply a 1 pound cut of shellac( twice the alcohol ) this fills the area between the fiber slightly making them stick together.

Sort of the bottom line is that any deficiency in techniques is magnified by softer woods.
Excellent technique may still have some tear out.

Al

 

[Dean Center]

Bob,
The answer is, it's cottonwood. Most of the turners in our Bozeman club won't turn it for exactly the reasons you note. Sometimes there is good figure at the base and it might be worth the effort, but not for the run of the mill cottonwood. On the other hand, we sometimes get nice poplar, and aspen is often very nice to turn, even though cottonwood and poplar and aspen are all part of the Populus genus.

Go wander around the older parts of the Fort and see if you can find some box elder or maybe some fruit wood to turn. There also may be some maple or ash or other hardwoods over in Glasgow that homeowners are going to cut down and would let you have. Any of those would be way more fun than cottonwood. If there's a tree service in NE MT, give them a call, they may be your new best friend.

BTW, I was up in Ft. Peck a couple months ago for some pretty good salmon fishing. Hope to get back up for walleye through the ice some time this winter.

 

[john lucas]

Around here Box Elder can be like that. It must vary with the trees location because I've turned some Box elder without a hint of trouble and other stuff fights me worse than almost an thing.
When turning a side grain bowl there are two areas 180 degrees from each other that almost always give more problems than the rest of the bowl. This is where the gouge is cutting uphill against the grain. Looking at the wood so the grain is horizontal this would roughly be the 10 oclock and 4 oclock areas. I have several techniques I try. First of course is to freshly sharpen the tool. This is one time when I will hone the gouge. If that doesn't work I reach for a tool that has a sharper cutting edge angle. I have bowl gouge with the stewart Batty grind that is 40 degrees. My normal bowl gouge is around 50 at the nose. If this doesn't work and the area in question can be reached while still rubbing the bevel I go to my spindle gouge which usually has around a 35 degree angle. If that doesn't work I try the Hunter Osprey or a Hunter #5 which have somewhere around 27 to 30 degree polished bevel.
Other solutions. The quickest is to simply spray water on it. Sometimes that acts as a lubricant and helps it cut clean. I often soak the area with 50/50 solution of lacquer and lacquer thinner. It takes a minute or so to try but will often stiffen up the fibers enough to cut cleanly. It bad cases I use thin CA. I try to stay away from that because it's nasty stuff and expensive but it does work.
Other solutions. Try turning in reverse and cut on the opposite side of the bowl. Usually this cleans up the bad area but introduces another bad areas. This is because you are still cutting against the grain on 2 areas but sometime it will produce less tearout or raised fibers than the original direction. Try shear scraping with a freshly sharpened round nose scraper held at a pretty steep angle. Usually takes quite a few passes with this tool and you may have to refresh the burr but it works.
Last but not least. turn off the lathe and use a round cabinet scraper by hand. This usually leaves a low depression and sandpaper will bounce over it when you get to the sanding stages. After I get rid of the tearout I feather the surrounding area with the cabinet scraper to lessen the shape of the depression. You may have to sand that area with the lathe off since the sandpaper will glide over it with the lathe on and not hit that spot.
Hope you have success. I've seen some awfully beautiful cottonwood pieces from other turners over the year.

 

[Odie]

Funny......I just roughed a 14% MC cottonwood burl bowl yesterday. As others have said, this wood is soft and hard to get a decent cut. In the photo, you can see some tearout in the interior, and I can see this one is going to be a challenge. You can generally get a cleaner cut with higher rpm's......provided the usual sharp tools and good presentation. Think of it this way......take a sharp knife and take a swipe at a piece of paper. The faster the blade passes through the paper, the cleaner the cut. The same principle applies to lathe tools on wood.

ko

 

[john lucas]

Odie I was talking to a Japanese paper cutting artist on how they use their knives. The trick to cutting through paper is (and this is not surprise once you think about it) cutting downhill with the grain. In other words what they do is tilt the knife so it's not cutting perpendicular to the paper. By tilting it at an angle it shears the fibers better, cuts easier and cleaner. DUH. Why didn't I think of that years ago. Relates to our woodturning very well however.
Al mentioned above that a 1/4" gouge gets sharper than a 3/8" gouge. Not sure he actually meant sharpen in terms of the actual edge sharpness but probably that a smaller radius will cut a little cleaner. At least that's my experience and I think Jimmy Clewes said the same thing when I was watching his long stem goblet demo. As much as I love the skew on rare occasions it would not cut squirly wood grain real clean but I could take my 1/4" spindle gouge and cut it as clean as can be. Both have about the same cutting angle and I sharpen to the same degree. So my conclusion is it has something to do with the small radius. Doesn't seem real logical since I'm taking roughly the same size bite out of the wood with either tool but I've tried it several times with the same results. Of course on bowl interiors tool chatter can become a problem when hanging a smaller tool over the tool rest.

 

[Odie]

Odie I was talking to a Japanese paper cutting artist on how they use their knives. The trick to cutting through paper is (and this is not surprise once you think about it) cutting downhill with the grain. In other words what they do is tilt the knife so it's not cutting perpendicular to the paper. By tilting it at an angle it shears the fibers better, cuts easier and cleaner. DUH. Why didn't I think of that years ago. Relates to our woodturning very well however.
Al mentioned above that a 1/4" gouge gets sharper than a 3/8" gouge. Not sure he actually meant sharpen in terms of the actual edge sharpness but probably that a smaller radius will cut a little cleaner. At least that's my experience and I think Jimmy Clewes said the same thing when I was watching his long stem goblet demo. As much as I love the skew on rare occasions it would not cut squirly wood grain real clean but I could take my 1/4" spindle gouge and cut it as clean as can be. Both have about the same cutting angle and I sharpen to the same degree. So my conclusion is it has something to do with the small radius. Doesn't seem real logical since I'm taking roughly the same size bite out of the wood with either tool but I've tried it several times with the same results. Of course on bowl interiors tool chatter can become a problem when hanging a smaller tool over the tool rest.

Hiya John.......

Yes, of course......as I said in my post above yours, sharpness and presentation has something to do with it, too 😀

The paper and knife example is a good one, as I've proven this to myself.....both with paper and knife, and on the lathe. Speed is something that is directly related to the cleanness of the cutting action on a lathe. I don't know if it would be a help for Bob's particular needs......too many other things could be involved in the equation to know that.

ko

 

[Odie]

You know.........I suppose I should mention that what I'm saying isn't the faster and faster the rpm is, the resulting cleanness of the cut will be better proportionally. There is a point where an increase of speed will have no effect on the effectiveness of the cut......but, too slow will definitely result in a lesser degree.

ko

 

[stu senator]

To cut a tomato you slice, not press harder.

This is similar to shearing to get a better cut in softer material.

Stu

 

[Odie]

To cut a tomato you slice, not press harder.

This is similar to shearing to get a better cut in softer material.

Stu

Yep, very true, Stu.......😀

To cut wood on the lathe you also slice, and is a product of presentation skill and sharpness. Since wood is much harder than a tomato, and different pieces of, and species of wood require different solutions, the speed at which you slice is a piece of the equation......provided sharpness and presentation are at the optimum, of course. In particular, when bowl turning, where end grain, long grain, and figured grain alternate, the speed of the cut will be subject to the skill and applied experience of the operator. There are no rules cast in stone, but speed is certainly an influential factor.

Since any particular speed may not be the most favorable, and the best speed will vary with the variables and conditions, it's up to the operator to use his experience to determine what the most favorable speed is.

ko

 

[Bob Strand]

Bob,
The answer is, it's cottonwood. Most of the turners in our Bozeman club won't turn it for exactly the reasons you note. Sometimes there is good figure at the base and it might be worth the effort, but not for the run of the mill cottonwood. On the other hand, we sometimes get nice poplar, and aspen is often very nice to turn, even though cottonwood and poplar and aspen are all part of the Populus genus.

Go wander around the older parts of the Fort and see if you can find some box elder or maybe some fruit wood to turn. There also may be some maple or ash or other hardwoods over in Glasgow that homeowners are going to cut down and would let you have. Any of those would be way more fun than cottonwood. If there's a tree service in NE MT, give them a call, they may be your new best friend.

BTW, I was up in Ft. Peck a couple months ago for some pretty good salmon fishing. Hope to get back up for walleye through the ice some time this winter.

Thanks for the info. And yes, cottonwood is cottonwood, it is what it is but it always tempts me with some nice translucense or grain. I may try the 50/50 lacquer trick that was mentioned below. I'm working on some Box Elder from up by Big Timber and have some aspen from the Crazies out of Wilsall but its really wet. Another discussion.

 

[Bob Strand]

Thanks for the replies on the cottonwood dilemma. I'll try to incorporate some of it. I'm new to the computer aspect of this forum but hopefully I'll get the hang of it. Again, thanks.

Bob