Depending on what is underneath your wood floor, you may be able to put in a pad or preformed pier pads, as close as you can, to be directly under the feet of your lathe, and add more vertical posts to the beams. Even 3 inch boards will flex under spinning loads. It may help, but for sure it wouldn't hurt. Some times pier pads, and the beams, and the posts will move a bit due to settling and seasonal movement, which is one reason why they use more engineered beams now.

robo hippy