lathe vibration

[jeff oldham]

i have a jet 1221 vs and i have been turning bowls and i havent notice it on other bowls but when i turn it up about 1800 rpm everything starts shakening really bad,,,vibration that is and i have it mounted to a cart i built on wheels,,,the bowl is completely true,,,i took the bowl off and just used the chuck and turned it up,,no vibration,,,i even put blocks under it to raise it off the wheels,,,still so much vibration,,i tried different chucks and no vibration when i turned it up,,,,i cant see any vibration in the spindle when i turn it up without the bowl on the lathe,, and like i said the bowl is true when i put it back on,,,but the vibration is there,,,can anyone please help me,,,and the lathe is bolted tight to the table,,,do i need a new lathe,,,help please

[Edward Weber]

Just because the bowl blank is true, it doesn't mean the weight/density in the blank is uniformly dispersed.
A perfectly round blank can be heavier on one side than the other.

[Bill Howatt]

What Edward said.

[Thomas Wilson80]

Agree with the above comments, plus 1800 is pretty fast for even a small bowl. I think Dale Nish came up with a formula of safe turning speeds - diameter x RPM should fall between 6000-9000 (at those levels, supposedly the blank will fall down and not projectile up). If you’re at 1800, your bowl should be 5” or less. The faster you turn, the more likely to have vibration.

tom

[Kevin Jenness]

If your lathe is shaking slow it down. How big is your bowl? If you do the arithmetic you will find that rpm x diameter = 9000 is the equivalent of about 27 mph rim speed. How fast do you want that chunk of wood to be going as it separates from the lathe and sails past your head?