Lathe stability on shop floor

I’m in the process of moving my shop to a back room in my garage (thinking this will be easier to heat). The problem is, it’s a raised wooden floor (about 15” to 8” off the ground supported like a deck and the floor itself is plywood). I threw a couple 2x10s under my powermatic 3520 to distribute the weight) I’m still getting enough shake/vibration when running a dried roughed out bowl that Is going to bother me and make me feel like I may get motion sick from the shake.

Any suggestions on reinforcing, strengthening and strengthening the floor without breaking the bank?

Thanks in advance
(I may cross post this on the shop threads)

Are you able to remove the plywood under the lathe? If you can i would put blocks under the floor joists to add extra support under it then put the plywood back.

Yep, I can remove the plywood... I may have to start with that

I faced this in my barn where the floor was full 3x10 boards laid over joists that were 3x10, 12" OC-- a sturdy floor meant to support horses. It shook like crazy-- the whole barn vibrated when turning a big, out of balance log. I put building jacks under each of the joists closest to where the legs sat (4 total), and bolted the lathe down, it helped, but there was still a lot of vibration. Finally I rearranged the shop to move the lathe to the part of the barn that was slab on grade, positioned the lathe so that the legs were on top of the flat 2x4 sleepers under the plywood subfloor and hardwood flooring, then bolted the lathe down into the underlying concrete with continuous support. Problem solved, no vibration due to the lathe not sitting firmly.

If you can access the underside of your structure I'd suggest either pouring a concrete foundation (just a big block of concrete) or putting four 8-10" sonotube columns, one under each of the leg attachment points so that your lathe can sit on a solid concrete foundation. A lot of work, but I expect you'd be happy with the result.

My lathe sits on a plywood floor with a basement under it. It's also at probably the weakest part, at the end of a stairwell opening. I have a Grizzly G0766, which weighs about 580 lbs. I built a wooden box attached to the legs about 3" off the floor that holds 4 40-lb bags of sand. with the box and sand my machine weighs about 760 lbs. My lathe is not bolted to the floor. The sand made a huge difference. My lathe is very stable unless you have a big (~50+lbs) out of balance piece of wood on it. I did put a jack post under the outside corner of the stairwell opening to support the floor at that cantered corner.

In your case, depending on how the boards you put under the lather are installed, they may make matters worse because they may flex with the vibration if not perfectly flat to the floor in all areas. If you want to leave them, I suggest screwing them down to the floor every 6 inches or so in all directions to remove/pull out any unevenness. Concrete poured between the joists will also help, but may require doubling up your floor joists to support the weight. The goal is to dampen the vibration (by means of mass). Try adding sand down low first. You many find your floor is sufficient as is.

Do you think it's the plywood or the floor joists that's your problem? If the joists are strong then do you have any side to side range? If so you could try to move it so both legs are as close as they can be to the floor joists. Are you ok with making changes to the floor that will not be easy to undo? If so I would remove the 2x10s and get a sheet of 3/4" (or thicker) advantech flooring and some sub floor glue. Glue and screw it to the existing plywood. An alternate idea would be to use hardwood decking like Ipe. It's very dense and heavy. If you were to screw it on top of the plywood to the joists It'll most likely solve your problem.

If the joists are a problem then I think your lease complicated way to solve it would be to take a circular saw and cut the plywood out from under where the lathe would go. Then, like Chris said, put blocking under where the feet go all the way down to the cement.

You could also put pieces of 2x10's between the joists under the lathe spaced apart every 2 to 3 feet. That could help by tying all the joists together to cut down on side to side movement.

I took a brut force method.

Cut 12" dia holes in the floor, 2 at the headstock about 4 feet apart, 1 at the tailstock
I got through to the dirt under the shed. Then dug down a few feet with a post hole digger.
Sunk a sono tube into the dirt, up to the height I needed for the lathe
Then filled the sono tube full of concrete, sunk large threaded rod into the concrete
Mounted a square steel tube across the two posts at the headstock, then bolted the lathe's headstock to the steel cross tube.
Similarly for the tailstock end.

And.....there's zero vibration, even with huge pieces.

bolted the late to the

I like this idea!