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 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
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.
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!
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.
In article , email@example.com
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.