A different Torsion box question....

[Mark Rios]

Actually a couple of them. I am starting to build one using the info from the David Marks episode that was linked in Craigs thread.


1) Would it be okay to cut a hand hold into the bottom side, center of the table/box? In the center of one of the hollow spaces?
I need to be able to store a tool this big standing on edge and would like to make it easier to move around.


2) Could someone explain "winding sticks", their use and purpose? Are they absolutely necessary?
If I understand correctly, one sights along one winding stick and looks across at the other. Is sighting another edge five feet away really as accurate as a dead-on level and double checked with a second dead-on level? I would figure it would be necessary to level not only in the length and width directions but also diagonally.


3) Why do they suggest 3/4" MDF for the frame? Why wouldn't 1/2" (like the rest of the structure) of 5/8" work?


4) Does the mahogany edgeing have anything to do with the strength or longevity of the box or is it only for aesthetics?

Thanks very, very much for any help!

[Jim Hinze]

1) Would it be okay to cut a hand hold into the bottom side, center of the table/box? In the center of one of the hollow spaces?
I need to be able to store a tool this big standing on edge and would like to make it easier to move around.

I'm not sure if the 1/2" skin would support the weight of the box for that purpose. I would recomend perhaps doing it toward the edge in a hollow so you could use 2 hands to lift up on the frame...

[/quote]
2) Could someone explain "winding sticks", there use and purpose? Are they absolutely necessary?
If I understand correctly, one sights along one winding stick and looks across at the other. Is sighting another edge five feet away really as accurate as a dead-on level and double checked with a second dead-on level? I would figure it would be necessary to level not only in the length and width directions but also diagonally.
[/quote]

It is my understanding that using winding sticks to compare across a distance is still more accurate. All you really need are 2 strait edges (e.g. 2 levels) to site down. Could also be 2 rulers, 2 pieces of MDF cut and painted different colors...

3) Why do they suggest 3/4" MDF for the frame? Why wouldn't 1/2" (like the rest of the structure) of 5/8" work?

My guess would be for weight, glue area, and stability. The general idea behind the torsion box is a solid, heavy core skinned by thinner material to keep the weight down. 3/4" internal with 1/2" skins fit that bill. You could also use 1/4" MDF for skins.

4) Does the mahogany edgeing have anything to do with the strength or longevity of the box or is it only for aesthetics?

Strictly for aesthetics. I edged mine with some more MDF... You could use virtually any hardwood, MDF or Plywood.

[Rick Lizek]

I first learned about the torsion box in an article by Ian Kirby in FWW many years ago. I find that as info get passed around it changes a bit each time. The key to a torsion boxes strength is the height of the frame pieces and the skin being glued to the frame. 3/4" pine with 1/8" luan skins yields a very strong light weight T-box. I've seen folks talking about using half lap joints to assemple the frame. Kirby just used staple to hold the frame together. The hardest part is finding a flat reference surface to glue up a torsion box. I've glanced at the Marks site on torsion boxes and it looks pretty detailed. I'd still recommend folks read Kirby's original article on the subject. MDF is more stable and there is no reason you couldn't use 1/2" or even ultralight MDF. I have some literature on an innovative bench Kirby made from a torsion box which doubled as a veneer press with curved cauls made from MDF.

I had a torsion box about 3" thick with 1/8" luan skins, 1/2" MDF core and laminate on both sides that was stored in an unheated damp garage for 5 years and it's as flat as the day I made it.

[Dave Richards]

"The hardest part is finding a flat reference surface to glue up a torsion box."

That would be my challenge. I don't have a flat surface on which to build one.

[Rick Lizek]

http://www.diynetwork.com/diy/ww_mat...278181,00.html
Not really that difficult.

[Mark Rios]

I first learned about the torsion box in an article by Ian Kirby in FWW many years ago. I find that as info get passed around it changes a bit each time. The key to a torsion boxes strength is the height of the frame pieces and the skin being glued to the frame. 3/4" pine with 1/8" luan skins yields a very strong light weight T-box. I've seen folks talking about using half lap joints to assemple the frame. Kirby just used staple to hold the frame together. The hardest part is finding a flat reference surface to glue up a torsion box. I've glanced at the Marks site on torsion boxes and it looks pretty detailed. I'd still recommend folks read Kirby's original article on the subject. MDF is more stable and there is no reason you couldn't use 1/2" or even ultralight MDF. I have some literature on an innovative bench Kirby made from a torsion box which doubled as a veneer press with curved cauls made from MDF.

I had a torsion box about 3" thick with 1/8" luan skins, 1/2" MDF core and laminate on both sides that was stored in an unheated damp garage for 5 years and it's as flat as the day I made it.

WELLLLLL...........where's the article? Is it available online or do I have to buy it?

DAVE: They go through the set-up process to establish the flat surface in the DIY article. Just patience and a little time.

I'm still a little fuzzy on the winding sticks though. But a very BIG thanks to Jim for the detailed reply. Very helpful. Thanks.

[Rick Lizek]

http://www.taunton.com/store/pages/fw_toc_032.asp
It might be available in the article compilation editions. Issue #32 JAN 1982.

[Dave Richards]

Mark, thanks.

Maybe this helps on the winding sticks? I just did it quickly.

Two boards with winding sticks on them.


Flat board looking from the end. Note winding sticks are parallel.


Warped board with sticks. I exagerated it so you could see it easily.

[Mark Rios]

Thanks very much Dave. That helps alot. Very kind of you.

[Tom Donalek]

Here's another nice illustration of the concept of winding sticks:

http://www.leevalley.com/wood/page.a...76&cat=1,41182

Also, in terms of using lighter weight materials for a torsion box, you can compensate by making it deeper (a.k.a. 'thicker') The strength and stiffness of the box increases as it gets deeper/thicker. If you want to use lighter/thinner materials for the box in order to be able to move it around, then you may want to make the whole thing an inch or two thicker to compensate. Then again, as long as you don't plan on doing things like standing on it, really leaning hard against it or assembling really heavy items on the box, this might be overkill.

[Mark Rios]

Here's another nice illustration of the concept of winding sticks:

http://www.leevalley.com/wood/page.a...76&cat=1,41182

Also, in terms of using lighter weight materials for a torsion box, you can compensate by making it deeper (a.k.a. 'thicker') The strength and stiffness of the box increases as it gets deeper/thicker. If you want to use lighter/thinner materials for the box in order to be able to move it around, then you may want to make the whole thing an inch or two thicker to compensate. Then again, as long as you don't plan on doing things like standing on it, really leaning hard against it or assembling really heavy items on the box, this might be overkill.

Well...yes... now that you mention it I would want it to support a couple of hundred pounds at least. So, instead of 3" inner pieces I'll go 4". I'm planning on making the box 42" x 66".

[Andy Henriksen]

Not that I've ever used winding sticks, but a good explanation of why they work is that they exagerate the twist in a board because they extend out beyond the width of the board. I would guess even on a wide application like this, though, the contrasting colors, and being up above the work piece would still make them beneficial.