Torsion box strength?

[Jay Yoder]

I have heard alot about torsion boxes and their inherent strength...so i am contemplating building a thin box to jockey my 48" tiller around. It weighs about 350# and is about 50" wide. I was thinking of using 3/4" bc ply for the skins and 1x2's or 2x2's for the frame. I am planning on spacing the frame members in 12" squares or maybe 16". Is this going to be adequate to support and move this around? i think it will be...any guidance would be greatly appreciated!!

[Greg Hines, MD]

I have heard alot about torsion boxes and their inherent strength...so i am contemplating building a thin box to jockey my 48" tiller around. It weighs about 350# and is about 50" wide. I was thinking of using 3/4" bc ply for the skins and 1x2's or 2x2's for the frame. I am planning on spacing the frame members in 12" squares or maybe 16". Is this going to be adequate to support and move this around? i think it will be...any guidance would be greatly appreciated!!



I guess I do not understand what you mean by "building a box to jockey a tiller around"? Do you mean that you are going to be putting it on wheels to move it around, or using it as a sled?

That said, the strength of a torsion box is the connection between the skins and the frame. Glue and nails will make it strong enough to hold a lot with skins made of 3/4" plywood, particularly with a smaller grid size.

Doc

[Jay Yoder]

i have a Steiner tractor with a tiller which mounts on the front. I am building an overgrown shelving unit for the attachments, and am putting them on wheels to slide in and out to be picked up by an overhead hoist and lowered to ground...

[Greg Hines, MD]

i have a Steiner tractor with a tiller which mounts on the front. I am building an overgrown shelving unit for the attachments, and am putting them on wheels to slide in and out to be picked up by an overhead hoist and lowered to ground...



It would probably be fine, but I would use smaller grids.

Doc

[Scott Vigder]

Use smaller grids, in the neighborhood of 7"-8".

[Jacob Reverb]

the strength of a torsion box is the connection between the skins and the frame. Glue and nails will make it strong enough to hold a lot with skins made of 3/4" plywood, particularly with a smaller grid size.

I'm with Doc here but would also add that the strength of a torsion box also depends on the distance between the skins...the "beam height" or "web length," so to speak. Think of an "I" beam; the taller it is (i.e., the longer the "web"), the stronger it will be. That said, for 350#, I think I would make the grid smaller (say 6" or 8") and make the web height at least 3" or 4". Good luck.

[Joe Jensen]

The 3/4" Ply won't add that much strength. Would a pallet work, or do you need something different for the loading system? If a pallet would work, why bother with a torsion box?

[Tom Veatch]

Unless you have some need for high torsional stiffness - which is the basis of the design of a torsion box and, incidentally, why it's called a "torsion" box - then I'm with Joe Jensen. A simple pallet is quite sufficient, and likely to be better suited for the application as I understand it.

[Jacob Reverb]

Come to think of it, Joe and Tom are probably right: If you're using a forklift to raise and lower the load (or if the span between supports is no more than the distance between the forks of a forklift) a pallet should work fine.

As Tom says, a torsion box is all about "stiff" more than "strong" per se. Can you tolerate a little bit of strain (bending) in your "shelf"?

[Rich Engelhardt]

Hello,
Harbor Freight has a movers dolly for ~ $15.00, rated for #1000.
Cost of 4 swivel castors alone is nearly that much.
It's ~ 30" X 18".

[Todd Bin]

There are lots of comments on Torsion Box. A torsion box is not as strong (in terms of total deflection) as a solid piece of wood of the same size But it is much lighter. For example, you would get twice the deflection but it would weight 1/4th as much. Torsion box is all about strength to weight ratio.

What makes the Torsion box dimensoinally stable is the fact that it is made from MDF

If you want more engineering knowledge about the torsion box then I highly recommned "More woodworker's Essential facts, formulas and short cuts." I have posted the Amazon link below. There is a whole chapter devoced to the Torsion box.

http://www.amazon.com/Woodworkers-Essential-Facts-Formulas-Short-Cuts/dp/1892836211/ref=sr_1_1?ie=UTF8&s=books&qid=1213279177&sr=8-1

[Jason Roehl]

A torsion box doesn't have to be made of MDF...the OP is talking of using 3/4" ply. In my thinking, 16" squares for the cross-members is plenty. When it's all said and done, 350# is not that much--especially, because that probably won't be a point load, but at least 3-4 contact areas, and probably towards the edges. Heck, two sheets of 3/4" ply glued together would hold that easy, though there would be some deflection. Glue it and screw it and be done with it. Don't over-think it, this ain't rocket science. I'd use 2x2s for the added glue surface, but I'd probably just rip some relatively clear 2x4s in half to make them.

[Tom Hargrove]

I have a client that distributes power equipment. They told me that tillers are shipped on pallets, so a pallet should work fine as a base.

They also suggested the metal crates or skids that rider mowers are shipped in. Some dealers may give you one, or sell it to you for scrap value. You can put casters on it and it should work fine.

[chris yount]

We recieve parts including 1/2 ton gear drives at work on pallets made of pressure treated lumber.The bottom runners are 4x4's or 4x6's the decking is 2x6's.These are pretty strong screwed together .If you were to dado the 2x6's then screw these down with some construction adhesive it would be an extremly stout and inexspensive solution to your problem.

[Jay Yoder]

pallets would work, although not sure how well. I am currently modeling it in 3d solid autocad. i will post shots of it when done...i have 4 different alttachments to fit in roughly 6'-0" wide x 50" deep x ~9'-0" high. I am in the process of adding on a 12'x20' garage and did not realize how much room the attachments and the tractor took. then i realized that if i could stack them vertically i have the room without taking up the whole space...what i am envisioning is a giant open shelf type unit in which the "platforms" can roll forward onto a "transfer platform" which in turn will be lowered to grade with a winch. The shelf would be easy other than the fact that they have to slide out to the point that they would clear the shelves below...I have to keep the shelves to a minimum thickness due to the stack up height of the attachments. I hope this made some sense...

[Peter Quinn]

One more vote for don't waste your time on a torsion box system to move implements. My Dad has numerous attachments for his john deere, he moves them around on pallets, some with casters attached, a few home made platforms. I'd be inclined to think more like a framer and less like an air craft engineer on this project; ie quick, strong and cheap.