Torsion box bottom for TS base cabinet

Just to say, you don’t NEED to torsion box, that is overkill for a sub 300 pound machine. Casters mounted to a 3/4” sheet will suffice. If you want it to be super heavyweight, add some 2byfer stringers, or cross bracing.

-- Think safe, be safe

Casters mounted to a 3/4” sheet will suffice.

Even if I’m talking a 6 foot long span from one end to the other? ;)

I’ve made quite a few saw bases with torsion box bases, constructed from 3/4” and 1/2” MDF. The one that I made for my miter saw, about 6’ long, I initially made with open pockets on the corners for casters. I would not do it again, not enough strength.

Not enough strength, how? Bolt/screw holes coming loose, or the corners/ears deflecting, or something else? Do you think it would have held up if you’d used plywood rather than MDF?

FWIW, This project is pretty similar to what I have in mind.

The point of a torsion box is for stiffness more than strength, but I think it’s appropriate to your task. I think embedding casters so they attach to the top skin needs to be done with care, as the usual attachment of the top skins would not be sufficient. For the inset casters I would add at least another layer plywood, attached not just to the top surface, but also to the ribs on all sides to transfer the force. Usually, the strength of the torsion box is due to the skins and their attachment to the spacing ribs that resist shear. For this purpose, continuous ribs the long way to carry the load would help.

I added such continuous rib reinforcement in an 8’ long torsion box that serves as the base for a lumber rack that can be moved, luckily rarely. It’s made with 2×4 ribs (long ones full length) and 3/4” plywood top and bottom skins and 5” casters. I not only didn’t inset the casters, but I reinforced their attachment points with another layer of plywood on the bottom. It’s not pretty, but in good shape after more than 20 years of carrying a lot of weight.

-- Alan in Wisconsin

Not enough strength, how? Bolt/screw holes coming loose, or the corners/ears deflecting, or something else? Do you think it would have held up if you d used plywood rather than MDF?

The corners bowed upward despite having a cabinet screwed above them. About 1/8-3/16”. 3/4” ply might’ve held up a little better.

I eventually relocated the casters inwards, directly under the boxing.

obviously, the corners here above were not part of the torsion box.

-- Sylvain, Brussels, Belgium, Europe - The more I learn, the more there is to learn (and that is nice)

obviously, the corners here above were not part of the torsion box.

- Sylvain

OP said he was considering this

...some people essentially make an open pocket at each corner for the casters, so they attach to the upper skin, rather than the lower and reduces the overall height of the base by several inches.

I find the idea kind of intriguing… but I wonder how much (if any) that compromises the strength of the torsion box itself?

And I’m advising against

You don’t need a torsion box base. If properly designed, the whole cabinet Is a torsion box.
If you put the casters under the bench, you will have issues accessing the lock levers. If you are going to use that type of roller, attach them to outriggers so you can reach the levers.

You don t need a torsion box base. If properly designed, the whole cabinet Is a torsion box.

For it to be ‘properly designed’ as a torsion box, the entire cabinet would have to be enclosed, with no doors or drawers. No thanks, pass.

If you put the casters under the bench, you will have issues accessing the lock levers. If you are going to use that type of roller, attach them to outriggers so you can reach the levers.

Yeah, that was/is a concern – I wouldn’t be able to reach all four casters, depending on which way they rotated as the cabinet was moved into place. Then again… with a couple hundred pounds of saw, and another hundred + (at least) of cabinet and ‘stuff’, having all four locked might not be entirely necessary. Probably a good idea, but not 100% required. IIRC, there are some funky specialty casters that also work as levelers that might mitigate that issue as well… but that’d involve getting down on hands and knees at each corner to snug them up, which is less than ideal.

The corners bowed upward despite having a cabinet screwed above them. About 1/8-3/16”. 3/4” ply might ve held up a little better.

Wow. That doesn’t look that heavy; I’m a little surprised it bowed that much. Thanks for the info!

You don t need a torsion box base. If properly designed, the whole cabinet Is a torsion box.

For it to be properly designed as a torsion box, the entire cabinet would have to be enclosed, with no doors or drawers. No thanks, pass.

- Monte Milanuk

Sorry. Trying to be brief, I assumed that everyone would understand and not take that literally. To be clear, I should have said that a well made cabinet with a plywood base and top and back, sides, and dividers creating compartments can be stiff enough to act as a torsion box. It will not twist or flex. A separate torsion box base is not necessary. Also, it does no harm if that is what you want to do. It just takes up space, uses more materials, adds complexity, and adds weight.