Uneven Rim on Bowl

When finishing a bowl, sometimes the side gets uneven. Do you think a bowl
rest would help? Your help would be appreciated.
Glenn Hodges
Nashville, Georgia
Reply to
Ghodges2
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I'm assuming you're talking about the effect of the nearly completed bowl moving out of a round shape (warping) as you're cutting/scraping. If your wall thickness is very thin and flexible then the bowl steady rest will help keep it in one place so your cutting/scraping goes cleanly. However, if it isn't very thin and flexible, then it won't help much. The problem could also be an in-adequate holding to the spindle (loose chuck for example) and you're getting some wobble. Make sure it stays put and the use of a bowl steady rest will *help* (but not cure) it from coming loose. You're better off to keep it from "moving" (going out of round shape) to begin with. You can do this by...
1) Completely drying the wood first before turning or, at least, rough turning and then completely drying before the final turning.
2) Keep the wood wet enough (stabilized) so the warping doesn't happen as you turn it to completion. This can be done by continually spraying it with water as you turn or using a stabilizer to various degrees of effectiveness.
3) Turn it to completion quickly (not RPMs) enough so that you don't give the wood enough time to dry unevenly and warp.
4) Using a more stable wood that doesn't warp easily.
No method is 100%. Just a few things to try.
- Andrew
Reply to
AHilton
Andrew pretty well covered it. One more thing to watch out for is to finish the bowl from the rim downward. Don't finish the part of the side closer to the bottom too thinly first because the part closer to the rim will have inadequate support and it will move under cutting pressures. A bowl steady would probably help but I have never tried it. The above was one of my all too common mistakes when I started bowl turning since I was concentrating on shaping without paying attention to the strength issue. Billh
Reply to
billh
You need to determine the nature of your problem first. If, indeed it is the standard narrowing across the grain on a face-turned piece, it will show two almost equal approaches on the end grain as you rotate it past the comparison point (tool rest), rather than a single, which would be the case if you had spindle or chucking problems.
If the piece is working against the chuck, you'll see that even the long grain can sometimes be the closest point. Here, this heretic would like to remind the spigot "torque" advocates of the crushability of wood fiber, and the propensity to split along annual rings to relieve compression stress. You can get a slight separation from a catch or a crush, and your piece can "flop" almost imperceptibly, or just rise slightly, producing a low spot. Prevention is in using no more force than is required to mate the surfaces, both face and interior, of the chuck to the piece. If you have a catch, regardless of what the piece looks like after, check for secure, especially for places where the piece seems to have climbed away from the mating surfaces you made. I like to use a dovetail recess versus a spigot, where a loosening can actually show as a close approach point which varies as the piece flops. Same prevention, same cure - don't try to bully the wood. I also find that on wet stuff, and woods prone to separation, a bit of CA allowed to penetrate into the spigot or under the dovetail can help. Of course, as I show on my page, I stay between centers until the last possible moment, so my problems will be less than those of a freely suspended piece.
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the spindle problem, you'll see a single close approach point on therim, but it will vary versus the TDC point on the headstock. Bearings andpreload most likely causes. Repair and run. I like the steady, because it can compensate for bearings - which should be quickly repaired in any case - and hold against squeeze or separation flop of the minor variety. I also like it for turning thin, but once again, I would like to express an heretical point of view and say that a fair curve is more easily achieved by continuous cuts from rim to base. I therefore keep walls pretty much the same after the initial hollow, so I can use my five-fingered calipers to check the fairness of the curve and the inside-outside match, if that's what I'm trying to achieve, or the rim to base increase if that's desired. I don't scrape for fair, I cut, and while any sanding is more than I'd like, I find I have less tearout, and no vibrational chatter if I use the steady and a cutting approach which does not push outward, but along the inside curve of the bowl. There will be some minor springback - ovalling - after dismounting, but nothing major, and the true bugaboo, thicker endgrain, is absolutely avoided.
One last observation. If you do get a steady, remember your sixth-grade earth science, and keep the wheels in contact perpendicular to the turning axis. Remember Coriolus!
Reply to
George
Do you mean while cutting with tools or while sanding ? If during sanding consider doing some hand sanding of the endgrain areas with the lathe stopped. The side grain sands a lot easier and faster than the end grain areas.
Scott Hogsten
In article , snipped-for-privacy@aol.com says...
Reply to
qedude
Use a sander which you can steady on the toolrest rather than the work itself. Bring the wood to the rotating paper, not the paper to the wood.
For me, a flex shaft powered by a 1/4 HP induction motor.
Reply to
George

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