a few things
- reverse the bowl against your chuck holding it in place with the
tailstock.

- True up the tenon or cut a new larger one. I bet you have enough wood
with the thickness but if all you have is the 50mm jaws on the super
nova you may not. With larger bowls I use the power grip jaws.

- While it is reversed also round of the outside of the bowl so when you
put the tenon back on the chuck it will be more balanced.

- Look for cracks. I find that little cracks in the wood can cause more
vibration resonance. You can almost tell that something is not right
when your bowl startes to sing. You can expect something to come flying off

- How fast are turning the bowl? Always start slow.

- Test your nova chuck by spinning it without anything mounted.

I've recently started putting my roughed turnings in a scale and putting
the information into excel so I can plot the drying rate and know when
it is dry.

Barry N. Turner wrote:
I put my roughed-out box elder bowl back on the lathe yesterday. Its about
10" in diameter by about 6" tall. It had dried some, so I had decided to
thin down the walls to hasten drying by taking a few hollowing cuts off the
inside of the bowl. Although the bowl walls are well over an inch thick (1
1/8"), I get a low frequency vibration when I start the cut near the rim of
the bowl. As I near the bottom, the vibration diminishes and goes away.

The bowl is mounted in my Super Nova chuck with a 2" stub tenon. The chuck
is tightly seated against the spindle....no plastic washer or anything. The
2" standard jaws are tight on the tenon. The tenon is intact....not cracked
or anything I am no longer using tailstock support as the bowl is now
hollowed. The Crown PM 5/8" Ellsworth grind gouge is freshly sharpened.
Still I get the vibration. Any ideas would be appreciated. Thanks.

Barry

PS Is it time for me to replace my Super Nova with a new Stronghold
chuck? Do I just need to put this blank on the rack, wait a few weeks and
let it finish drying before I come back to it?