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Torsion Box v Paulk

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Forum topic by FreeRangeWoodworker posted 09-26-2017 05:48 PM 610 views 0 times favorited 12 replies Add to Favorites Watch
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FreeRangeWoodworker

19 posts in 240 days


09-26-2017 05:48 PM

I am going to make an assembly table that needs to be dead flat. What are the pros and cons of making a torsion box vs a Paulk-style table?

-- Life is what you make of it.


12 replies so far

View Rick_M's profile

Rick_M

10275 posts in 2162 days


#1 posted 09-26-2017 06:35 PM

Does Paulk advertise his style as dead flat? He designs his stuff for contractor work and general woodworking. I would think that if “dead flat” made from wood is the requirement, your only real choice is an MDF torsion box.

-- http://thewoodknack.blogspot.com/

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clin

730 posts in 778 days


#2 posted 09-26-2017 08:58 PM

The Paulk workbench design is a torsion box. But, I don’t believe it is meant to be an unusually flat surface. Rather, a light weight, portable work surface.

A torsion box is essentially trying to approximate the rigidity of a solid slab of material, with less material. It does this by effectively removing the material that contributes the least to overall stiffness. The Paulk design just has internal webs father apart and with some material removed from the middle of the webs to lighten them, and provide some access.

So, it’s just a matter of degrees between a Paulk build and what I think you’ve likely seen presented as torsion boxes.

Light weight (relative to the alternatives that perform the same), rather than flatness, is the primary feature of a torsion box. But because of how it is built it will retain the shape as built. This the advantage for us. It provides a way to build a flat surface relatively easily.

A torsion box will only come out as flat as the surface you build it on. So to create a dead flat box, you need a dead flat work surface.

The Wood Whisperer has a pretty good method for making a flat building surface. You will actually spend more time making this reference surface than the box itself.

https://youtu.be/1-Hbsou6cWo

While I used his approach to the reference surface, I did not for the webs in the box. Here’s a link to my assembly table LJ project.

Click for details

The only glue I used on the web-to-web joints was some CA (super glue) here and there for the odd web that had some bow and needed help staying flat. I didn’t want to have to push the skin and webs down when tacking in place. Even MDF can have some internal stresses.

Like Rick said, MDF is a good surface to use because the sheets have very smooth surfaces, so are very flat in that sense. And for an assembly table, that won’t get the heavy use of a workbench (I.E. beat on with a hammer etc.), MDF is plenty strong. Throw a layer of hardboard on top of that to create a sacrificial work surface if you want. Though you will loose flatness as the hardboard may not lay all that flat under it’s own weight.

-- Clin

View ArtMann's profile

ArtMann

629 posts in 598 days


#3 posted 09-26-2017 09:12 PM

I would recommend the torsion box table but I will caution you that the flatness depends entirely on how you build it. You have to use a level and a precision straight edge to make sure the bottom surface is properly supported and dead level across the entire surface before gluing up. You also need to take care with the internal grid to make sure it is uniformly thick. Unlike certain box construction, a torsion box is not self squaring.

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Madmark2

351 posts in 370 days


#4 posted 09-26-2017 11:11 PM

Use your saw top. It’s the biggest, flattest, stiffest surface in the shop.

M

View rwe2156's profile

rwe2156

2662 posts in 1262 days


#5 posted 09-27-2017 12:32 PM

The problem with using TS is its too small and who wants glue all over their machinery?

Ultimately, I think a torsion box assembly table has to be fairly stout (translation: heavy). MDF (although I hate the stuff) is undoubtely the best material for this use.

Check out the torsion box video by Spagnolo at Woodwhisper.

Had to do over, I would suggest you use formica laminate on top.

And don’t get too anal about the flatness ;-)

-- Everything is a prototype thats why its one of a kind!!

View FreeRangeWoodworker's profile

FreeRangeWoodworker

19 posts in 240 days


#6 posted 09-27-2017 04:46 PM

Thanks to all.

-- Life is what you make of it.

View waho6o9's profile

waho6o9

7981 posts in 2359 days


#7 posted 09-27-2017 04:56 PM

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FreeRangeWoodworker

19 posts in 240 days


#8 posted 09-27-2017 05:17 PM

Follow up question: Could I lay the bench out on the floor of my garage, which is flat, but not level?

-- Life is what you make of it.

View Rick_M's profile

Rick_M

10275 posts in 2162 days


#9 posted 09-27-2017 07:00 PM

Does the floor meet your requirement of “dead flat?” If not, you risk building a table that is not flat enough.

-- http://thewoodknack.blogspot.com/

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ArtMann

629 posts in 598 days


#10 posted 09-28-2017 03:58 PM

I just want to say that I don’t think MDF is necessarily the best material for constructing torsion boxes. It is much heavier than 1/2” plywood and it isn’t as strong (not that strength matters much in this application). I use quality 1/2” pine plywood for the interior mesh and use Russian Birch for the outside skins due to the superior strength and consistency. Why defeat the purpose of building a light and strong assembly by filling it with just about the heaviest construction material you can buy?

View clin's profile

clin

730 posts in 778 days


#11 posted 09-28-2017 08:28 PM



Follow up question: Could I lay the bench out on the floor of my garage, which is flat, but not level?

- FreeRangeWoodworker

It is unlikely your garage floor is anywhere close to flat. Level doesn’t matter, but dips in the range of 1/4” are not uncommon in concrete slabs. Of course a thicker skin (like 1/2” or 3/4” MDF), isn’t going to follow ever little dip in the floor, but you would still end up building in some significant irregularities.

In my build, I think I was less than 5 mil (0.005”) when done. This was based on using feeler gauges and a 4’ reference bar.


I just want to say that I don t think MDF is necessarily the best material for constructing torsion boxes. It is much heavier than 1/2” plywood and it isn t as strong (not that strength matters much in this application). I use quality 1/2” pine plywood for the interior mesh and use Russian Birch for the outside skins due to the superior strength and consistency. Why defeat the purpose of building a light and strong assembly by filling it with just about the heaviest construction material you can buy?

- ArtMann

I completely agree that there are better materials than MDF if weight matters. But lightweight isn’t necessarily a goal for workbench tops. And in some cases, heavier is better so the table doesn’t move.

-- Clin

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ArtMann

629 posts in 598 days


#12 posted 09-29-2017 02:59 AM

For a workbench top, I would only use 1-3/4” or more solid hardwood like Maple. Nothing less would be stable enough for my purposes. The OP wants to build an assembly table, which is a little different, and I am assuming he is going to the extra trouble of building a torsion box so it will be light. Yes/no?

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