the lathe itself weighs 200lb and the bench im building weighs about
another 100lb. is that enough to make it not dance with me while
turning big off center/not balanced pieces? or should i fill the two
pockets i made with sand to add another 50lb total?

Man, that's not enough to turn 5" weed pots. I have experimented
extensively with the weight issue, having owned several lathes and having
built several benches. Yeah, you can get by with 300 pounds, total, but
it is very, very far from ideal. If you build a big, sturdy bench with a
large (full length, full width) boxed-in container for sand, and then
start pouring in sand and using the lathe after each sandbag is added, you
will quickly realize that more weight is better, and better, and better.

A lathe really smoothes out and settles down for small pieces (5" - 6"
tall, 9" bowls) at around 700 pounds. For medium size pieces (up to 10"
hollow forms, 12" - 13" bowls) 1000 pounds seems adequate. Right now I
wouldn't own a lathe/bench combo that doesn't weigh at least 1000 pounds,
except for my mini-lathe, of course. It was a real eye-opener when I
first began experimenting with this, you've got to experience the results
to believe it, but it really makes a difference.

I remember when my Powermatic 3520 was delivered, I began using it as it
was, weighing 700 pounds out of the box. But then I put in a 16" wide
shelf, added another 350 pounds of sand, and the results were very much
more to my liking.

And I'm not talking about roughing large, out-of-balance blanks. I don't
do large work, and I do a pretty good job of rough truing before the blank
is ever mounted on the lathe. Even for general turning after the piece is
roughed and balanced, a heavy lathe is a joy to use. It really smoothes
out and makes all the turning steps more pleasurable. Massive weight is
the key to making your lathe perform the way it was meant to. Once you
try it, you won't ever want to go back to a lighter lathe.

-mike paulson, fort collins, co