Powermatic

I have had a Powermatic 4224 lathe for the last year and it has been an absolute pleasure to own. However, whenever I reach about 300 or 400 rpm when I am roughing out a decent sized bowl (14 inches) the lathe begins to vibrate and shake. It is always at about this speed regardless of the size of the piece. Once the piece is round, I can turn the speed up and it is fine.

What do you guys think it is? Are the pieces just out of round and too heavy for the lathe? Does it have to do anything with hitting the 'resonance frequency' of the steel in the lathe causing the excessive vibration? Any ideas how to solve this problem?

I also own a 4224---first thing check your bearings---do this with a mic whitout any thing mounted on the spindle----oh a question ---Which pulley are you running your drive belt---mine stays on the low rpm range.
Lets see what your answer is there are a few more things we can look at.

One of the leveling feet not sharing the weight of the lathe?

Is the lathe sitting on a solid slab of concrete?

Joe