About thirty days ago I turned a natural edge bowl 7 1/4 X 4 1/2 X 1/4 from green Sycamore. I produced nice clean shavings both inside and outside. I let it dry in a paper bag for thirty days and now I'm trying to finish sand it. Now for my problem - There are tiny pits both inside and outside, these are worst where the end grain meets the side grain. They are imposible to sand out. No matter what grit paper I use it seems to continue tearing in these areas. There are lines perpendicular to the grain in this wood which appear to be natural. These lines are most predominant in the problem areas. What's wrong?
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Turning green Sycamore
- Thread starter jwavem
- Start date
sycamore
Posting a picture always helps in the diagnosis. If you can get a picture uploaded, the opinions offered will be more on target.
Posting a picture always helps in the diagnosis. If you can get a picture uploaded, the opinions offered will be more on target.
From what you describe, it sounds like you're getting tear out at the downhill transition from side grain to end grain. The lines you described may be spalt or figure, both of which would increase this problem.
Figure that wood is basically a bundle of hollow straws. When you cut across them, the compress and distort. Now picture cutting across them at an angle. If the angle presses the ends of the straws into the side of the next straw, you get a cleaner cut. This is cutting uphill. If your cut presses the straws into shorter straws and pulls them apart, this causes tearout, and is cutting downhill. (somebody correct me if I've got the terms backwards)
When cutting side grain, you want to cut from the large diameter to the small on the inside and small to large on the outside, thus supporting all cuts with intact grain. When cutting end grain, the exact opposite is true.
My guess is that, now that your wood is drier, the grain has opened up a bit and is no longer supporting the cuts as well, leading to bits of wood tearing out. If there's spalt (rot) or figure (kinks in the straws) this will exacerbate the problem.
Best solution I've found is reversing the lathe for part of the sanding and rubbing past wax into the areas that are tearing. The wax lubricates the fibers so that they either cut or slip, not grab and tear. Don't bother waiting for the wax to dry to sand, and gob it on thick.
Good luck,
Dietrich
Figure that wood is basically a bundle of hollow straws. When you cut across them, the compress and distort. Now picture cutting across them at an angle. If the angle presses the ends of the straws into the side of the next straw, you get a cleaner cut. This is cutting uphill. If your cut presses the straws into shorter straws and pulls them apart, this causes tearout, and is cutting downhill. (somebody correct me if I've got the terms backwards)
When cutting side grain, you want to cut from the large diameter to the small on the inside and small to large on the outside, thus supporting all cuts with intact grain. When cutting end grain, the exact opposite is true.
My guess is that, now that your wood is drier, the grain has opened up a bit and is no longer supporting the cuts as well, leading to bits of wood tearing out. If there's spalt (rot) or figure (kinks in the straws) this will exacerbate the problem.
Best solution I've found is reversing the lathe for part of the sanding and rubbing past wax into the areas that are tearing. The wax lubricates the fibers so that they either cut or slip, not grab and tear. Don't bother waiting for the wax to dry to sand, and gob it on thick.
Good luck,
Dietrich
Re green Sycamore
Can't get a picture that shows the problem. This wood is not spalted or punky. The perpendicular lines appear to be a natural characteristic. It does look like tearout all though it sure felt like it was cutting clean. If it is tearout why won't it sand out?
Can't get a picture that shows the problem. This wood is not spalted or punky. The perpendicular lines appear to be a natural characteristic. It does look like tearout all though it sure felt like it was cutting clean. If it is tearout why won't it sand out?
R
Ron Sardo
Guest
jwavem said:
With only a 1/4" left on your present bowl, you are not going to have much wood left to work on to fix the problem. On the next piece try going all the way! That is, rough turning, final turning, sanding and finishing all in one session.
In the last few months or so I have completed 10 natural edge pieces that range from 1/16" to 3/8" thick. Yes they warp a bit, but that is part of the beauty.
BTW none of them cracked. . . so far.
Steve Worcester
Admin Emeritus
You sand the wood as if it were dry. It may take longer in the lower grits as you start driving water out. The sand paper will also clog alot more, so you will need a crepe block handy, or a soft wire brush (I like the crepe block better).
As far as finishing, you can do it the same too. The difference may be that if you are using a solvent based finish, like a lacquer, it may blush because of the trapped moisture. Waxes won't have that problem.
As far as finishing, you can do it the same too. The difference may be that if you are using a solvent based finish, like a lacquer, it may blush because of the trapped moisture. Waxes won't have that problem.
R
Ron Sardo
Guest
Steve Worcester said:
I use an old mouse pad, but where can you get a crepe block?
Wet Sycamore
Steve
The end grain on a wet turned Sycamore bowl is much darker and duller than the the rest of the wood. Should this go away if the bowl is sealed with a finish? I'm not trying to give you a hard time. In the past when I finish turned a bowl from start to finish, I always let it dry before sanding and finishing.
Thanks.
jwavem
Steve
The end grain on a wet turned Sycamore bowl is much darker and duller than the the rest of the wood. Should this go away if the bowl is sealed with a finish? I'm not trying to give you a hard time. In the past when I finish turned a bowl from start to finish, I always let it dry before sanding and finishing.
Thanks.
jwavem
Rockler or any similar supply store sells them. They are like jigantic eraserrs.Ron Sardo said:
Good Luck
Elizabeth
- Joined
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jwavem said:
Disclaimer - I've never turned sycamore, either the American or the maple they call Sycamore over in GB.
It sounds to me as if you are describing the prominent ray figure in sycamore. That's what those lines perpendicular to the annual rings are. The rays run radially (doh!) from center and help transport water and nutrients across the tree. They are also a built-in cleavage plane waiting for an opportunity to split.
The heat produced by sanding will open up "pits" at these weak points. The good news is, if you dampen them or let them equalize, they'll probably close and none the wiser, because the ray figure is right there to mask it. The piece will be weaker, so hopefully it's a looker not a user, where it might not survive a drop.
Woods like beech, which is a beech to gain cooperation from, red oak, and others with prominent ray figure are more or less prone to this. I've done some textured pieces by letting the sanded piece dry, and simply scrubbing with a terrain-following plastic pad for slick. The piece is full of ripples, including the areas around the rays.
I suspect the reason the end grain is "darker" on your bowl is because it's filled with water. That's the way the tree is built - to send water along the grain. Spinning helps move it pretty well. Then there is the natural difference between reflection off an area with more spaces than places, where the light can get trapped in those pores. Standard woodworking trick is to sand end grain a grit or so higher, to burnish and close it a bit so it won't take up its larger proportion of finish, looking more the shade of the face grain.
NB- Crepe blocks are about useless for for cleaning 2-3" discs, so I'd recommend a brass-bristled brush sold over in the plumbing department as a "flux" brush for them. Used with just enough force to remove the crud, it's almost as easy on the grit itself as the crepe.
R
Ron Sardo
Guest
Elizabeth Woodturner said:
Sometimes I'm slow. I thought you where using crepe blocks as a sanding block.
I use a crepe block to clean sanding belts all the time.
Thanks!
The perpendicular lines in the wood are rays - just like you would find in Oak but smaller. Try wet sanding. I spray the wet turned bowl with a sprayer full of water and then sand. Wet the sand paper first (spray it). Put a towel on the lathe bed first as it gets real messy. Keep applying water and keep cleaning your sand paper. I do this and then when the bowl is dry I dry sand it with fine grit paper to finish it off. Saves on the dust problem a bunch. Be advised it is messy.
On the dry bowl put some Danish oil or beeswax/mineral oil or ? and then try to make a finishing cut. This helps in the tearout areas. (Ray Key trick).
Hugh
On the dry bowl put some Danish oil or beeswax/mineral oil or ? and then try to make a finishing cut. This helps in the tearout areas. (Ray Key trick).
Hugh