wrote in message
oups.com...
I have a Delta 16" lathe that I thought had bad bearings or a spindle
that was bent because I get a lot of vibration especially on larger
bowls. Hats off to Delta, they sent me new bearings and a spindle for
free and a new belt (it was out of warrarty), but I'm still getting way
too much bounce when the bowl is turning. On a 12" bowl it's hard to
keep the tool edge on the wood! I have the supernova chuck and it
seems to hold the piece very well, but if something in the worm gear
was off would it cause the vibration? And if so how would I be able to
check it. I'm at the end of my rope in trying to figure this out. Oh,
and I have around 450lbs of sand on or in my lathe also. Any insight
from anyone would be a great help.


You've already checked for runout at the jaws? Easy enough to do by
clamping something to a toolrest and rotating by hand, checking for
consistent gap. Bjarte suggests extending the axis, which could introduce
more, even on a "known good" piece, but would also make any runout more
obvious. Crapshoot.

You're periodically snugging the jaws while making the turning? With the
smooth holds, where the force is spread over a broader area, it's not as
much of a problem as with the crush holds, where a misplaced tool can get
the whole out of whack with a catch and dig-in. Make sure you have a good
shoulder if gripping a tenon, and make sure you have full contact with it.
Make sure you have a flat bottom on your mortise if using an internal
dovetail, and make sure it's tight up against the nose of the jaws. If it
wobbles, snug, don't crank. Cranking can exacerbate your problem.

Use your tailstock until the last possible moment, when your bowl is at its
lightest and most round. Be sure to snug - not crank - your hold before you
release the tailstock, and as billh suggests, don't "ride" the bevel when
cutting. Pressing into the piece leads to following its irregularities.
Pressing into your unmoving toolrest and letting the wood cut itself against
your sharp tool leads to a round piece. Might as well compound the heresy
and say don't cut over about 600. With all kinds of kinetic energy
available, you can fool yourself into thinking your tool is sharp enough,
when in reality it's ripping the daylights out of things. When it rips, the
wood flexes and recoils.

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