MFT and torsion boxes

[JimTaylor]

I love it when “marketing” apply a name to a product. Makes it seem more valuable than calling it a worktop with bracing.

 

[Jacob]

If you have a large sheet opposite corners can droop, which would be a twist, or in torsion, so technically the box does provide some resistance to torsion as well as other bending forces.

But that applies to every structure involving sheets or boards. Every timber floor, every box ... and so on. Every workbench, every table....endless list. Every bread board.....
The term "torsion box" came about specifically in relation to hollow structures where torsion was the main issue; aircraft wings.

 

[Fergie 307]

Ì remember when the term "turbo" was the in thing. Suddenly everything had to be "turbo" to be trendy and cutting edge, even though in most cases it had b****r all to do with the product.

 

[Fergie 307]

But that applies to every structure involving sheets or boards. Every timber floor, every box ... and so on. Every workbench, every table....endless list. Every bread board.....
The term "torsion box" came about specifically in relation to hollow structures where torsion was the main issue; aircraft wings.

Ah the Fokker eindecker, lovely piece of design. And with an interruptor to allow that other great piece of engineering, the maxim gun, to fire through the propellor arc. Why are we always so ingenious when it comes to killing each other.

 

[paulrbarnard]

That sounds familiar!,....Which person does that describe & remind me of...?....Hmmm...!

I immediately thought a Dyson sphere would be needed rather than a torsion sphere for the volume of hot air available.

 

[Jacob]

Ì remember when the term "turbo" was the in thing. Suddenly everything had to be "turbo" to be trendy and cutting edge, even though in most cases it had b****r all to do with the product.

Does anybody put go-faster stripes on their turbo torsion boxes I wonder?
Every little helps.

 

[TheUnicorn]

I've been using a slab of 18mm hardwood plywood as a worktop with a friction fit down onto a pair sawhorses. There are a few 20mm holes for track saw use and when I clamp a piece down to it, I use F-clamps on the edge more often than not. But of course this single slab is no longer absolutley flat with a *very* slight camber to it (1mm or so) but still rather functional, so was thinking about torsion boxes to maintain the flatness.

The classic torsion box seemed to be made with several cross braces to make a number of "boxes", but an MFT makes use of lot's of 20mm holes for work handling and so those tend to be a single box the same dimensions as the top slab (no overhanging lip). What I'm wondering is why not do a box that is a bit smaller than the top slab and leave a lip for easy edge clamping? The ones I see require clamps at least 6" longer than otherwise.

I didn't post it in the other convo on torsion boxes as it's become mired in arguments mostly unrelated to my question.

this thread seems to have wandered away form your question, I was just wondering what direction you were leaning with your design now?

 

[JimTaylor]

If you use 4x2 to brace the worktop, you can put 20mm holes in the bracing around the edge and this would allow you to put your clamps through the bracing and clamp your work to the top. 18mm ply is not that strong and your clamps will probably damage the edge over time.

 

[brucew]

this thread seems to have wandered away form your question, I was just wondering what direction you were leaning with your design now?

I'm not in a hurry but am currently leaning toward an MR MDF sheet about 1400x750 so it will fit a workpiece as large as 1220x610mm with worktop to spare around all the edges.

Underneath would be a 12-18mm frame attached probably 100mm tall forming an open box (no bottom sheet). The frame would be inset perhaps 75mm from the edge all around and might put a cross brace corresponding to the centre of where the plunge saw guide rail would usually go.

On the front long edge I'd also put a 450mm long open box flush with the worktop edge and a t-track inset into the face in order to use ratcheting rail clamps to clamp a workpiece vertically (instead of a heavy moxon vice)

I'd use CNC Design's Pro Jig to set a minimal number of holes for workpiece/plungesaw referencing and some basic clamping, but haven't decided the starting set yet.

 

[Jacob]

I'm not in a hurry but am currently leaning toward an MR MDF sheet about 1400x750 so it will fit a workpiece as large as 1220x610mm with worktop to spare around all the edges.

Underneath would be a 12-18mm frame attached probably 100mm tall forming an open box (no bottom sheet). The frame would be inset perhaps 75mm from the edge all around and might put a cross brace corresponding to the centre of where the plunge saw guide rail would usually go.

On the front long edge I'd also put a 450mm long open box flush with the worktop edge and a t-track inset into the face in order to use ratcheting rail clamps to clamp a workpiece vertically (instead of a heavy moxon vice)

I'd use CNC Design's Pro Jig to set a minimal number of holes for workpiece/plungesaw referencing and some basic clamping, but haven't decided the starting set yet.

Sounds good!
Just add four legs and you have a very conventional table, but with a thin top. The legs are handy for joining the aprons and also keep the whole thing off the floor (obviously).
The Moxon vice and projecting lip problem is avoided with a conventional workbench by having an apron wider than your 100mm and flush with the top, no lip. Then a normal vice (flush to the apron) can hold pieces vertically, with added clamps or hold downs to the apron as necessary. The whole apron side of the bench then functions as the back jaw of the vice.

 

[brucew]

Sounds good!
Just add four legs and you have a very conventional table, but with a thin top. The legs are handy for joining the aprons and also keep the whole thing off the floor (obviously).
The Moxon vice and projecting lip problem is avoided with a conventional workbench by having an apron wider than your 100mm and flush with the top, no lip. Then a normal vice (flush to the apron) can hold pieces vertically, with added clamps or hold downs to the apron as necessary. The whole apron side of the bench then functions as the back jaw of the vice.

True, but I don't want nor have room for a heavy conventional workbench. I need one that I can lay flat against the garage wall when the space is needed, light enough to move for that purpose, yet sturdy enough for work. So my current 18mm top sits on sturdy wooden saw horses, held in place by four holes mashed down onto rubber bungs screwed to the top of the saw horses.

 

[Jacob]

True, but I don't want nor have room for a heavy conventional workbench. I need one that I can lay flat against the garage wall when the space is needed, light enough to move for that purpose, yet sturdy enough for work. So my current 18mm top sits on sturdy wooden saw horses, held in place by four holes mashed down onto rubber bungs screwed to the top of the saw horses.

OK understood.
I've done lots of work on saw horses alone, sometimes with a sturdy joist or similar clamped or nailed to the top.

 

[TheUnicorn]

my current 18mm top sits on sturdy wooden saw horses, held in place by four holes mashed down onto rubber bungs screwed to the top of the saw horses.

sounds like a nice quick way to mount the top, do the rubber bungs work to dampen vibration or was it just what was to hand?

 

[brucew]

sounds like a nice quick way to mount the top, do the rubber bungs work to dampen vibration or was it just what was to hand?

I just needed something that was dead quick and easy to easily disassemble but would keep the worktop stable whilst in place. It might minimally influence vibration, but I've not noticed. BTW: I've a steel washer on top of each bung to keep the screw secure without tearing at the bung. Had to cut the bungs shorter than stock so the worktop would be a few mil proud of them.

 

[brucew]

The Moxon vice and projecting lip problem is avoided with a conventional workbench by having an apron wider than your 100mm and flush with the top, no lip. Then a normal vice (flush to the apron) can hold pieces vertically, with added clamps or hold downs to the apron as necessary. The whole apron side of the bench then functions as the back jaw of the vice.

I've also thought to have the apron on the long sides be flush with the worktop but just stop 75-100mm short of the ends and then the end aprons completing the box be inset so my worktop clamping is primarily on the ends and my moxon alternative be mounted straight to the centre of one long apron instead of being an additional structure.

Too, I'd think that hardwood-throughout plywood would be stronger than MR MDF, especially if having a unsupported 75-100mm lip on the end for clamping. That's what I'm using presently for the single slab worktop.

 

[Fergie 307]

True, but I don't want nor have room for a heavy conventional workbench. I need one that I can lay flat against the garage wall when the space is needed, light enough to move for that purpose, yet sturdy enough for work. So my current 18mm top sits on sturdy wooden saw horses, held in place by four holes mashed down onto rubber bungs screwed to the top of the saw horses.

Depending on whether it would suit your needs, could you secure it to the wall with hinges, and have legs to fold out and support the outer edge when it's in use. You could have a suitable sized batten on the wall that it folds down onto, so the hinges aren't taking the weight.