# Torsion box grid



## Kathy36 (Feb 13, 2010)

Hi all, I'm building a Torsion box grid top. I would like to know, What is the best spacing for the grids? 
Kathy


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## jlhaslip (Jan 16, 2010)

What sort of material are you using, what size of table surface, and how thick?


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## Tony B (Jul 30, 2008)

What size and what will you be using it for? 
I have made them 10 foot long X 18" wide and stood in the middle of the span and deflected less than 1/8 inch. Hollow core doors use 1/8" plywood over a cardboard of sorts grid and are very stiff. So size and usage does make a difference.


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## Kathy36 (Feb 13, 2010)

I will be using 3/4" birch plywood and the size is 42" x 7' with cabinets for the base. An old friend also recommended you tube. Thank you. Kathy


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## Tony B (Jul 30, 2008)

Please understand that this info is not from engineered and calculated designs. It is what I would do. 
First off I'm going to assume that it will ne some kind of counter top or desk with access from both sides. Then I will assume that the cabinets will be around 18" wide and 42" long and the top will span across the 2 cabinets. That will leave an actual span of approx 4 feet. If that be the case, I wouldnt bother with a bulky torsion box design unless of course it will be a workbench. If it is a workbench, I would use 1/2" ply on bottom and 3/4" ply on top. The 'grid' would be 1/2" thick MDF cut into 1 1/2" strips.


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## Kathy36 (Feb 13, 2010)

Thank you for your advice, It is going to be a work bench and I figured the grids at around 4" apart. Tony B and jlhaslip you have been very helpful. Thank you again. 
Kathy


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## woodnthings (Jan 24, 2009)

*Consider a solid core door?*



Kathy36 said:


> I will be using 3/4" birch plywood and the size is 42" x 7' with cabinets for the base. An old friend also recommended you tube. Thank you. Kathy


A standard solid core 36" x 80" door birch faced is about $90.00 and could have a 1/2 MDF top secured making the overall thickness 2 1/4", very stout. That's what I've used for all my benches. I place them on legal size file cabinets with heavy duty roller drawers for storage underneath. You can use up to 4 file cabinets under each door. 
Unless you have your heart set on making a torsion box this is a convenient alternative. The doors may also come in a 42" width, 3' 6", as a special order. :thumbsup: bill


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## Kathy36 (Feb 13, 2010)

Hi Bill, I like that idea! I already started my top but I'm going to take your advice on my next bench in a few weeks I hope. You're still that tiger right off the bat from my first post. Thank you so much. 
Kathy and Sandy


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## Spindrift (Aug 20, 2009)

I use the smallest spacing I can. I do a test on scrap. Whatever my nailer or stapler can manage on the diagonal is what I use.

Closer is better until the point where you can't get the nail or staple in to hold the parts until the glue dries.

I have not used doors for clamping surfaces after I crushed the first one. If you are using this thing for a table top, doors are great. As assembly surfaces they stink. Not only do they crush but they peal, blister and get wavy with both solvents and water.

Built your own for assembly use.


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## Kathy36 (Feb 13, 2010)

Thank you for your advice, I am going to use the next top for assembly and finishing. I better rethink this now. Thanks again Spindrift. 
Kathy


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## woodnthings (Jan 24, 2009)

*Solid core doors don't "crush"*

Quote:
I have not used doors for clamping surfaces after I crushed the first one. If you are using this thing for a table top, doors are great. As assembly surfaces they stink. *Not only do they crush* but they peal, blister and get wavy with both solvents and water.

If covered with MDF they won't be subject to glue or chemicals, which can be flipped over for a new fresh surface when one side deteriorates.
:thumbsup: bill


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## Spindrift (Aug 20, 2009)

[Using add-layers] ... and they will not be flat.

Guys - the entire purpose of a torsion box is to form a stable, permanent reference surface for assembly and glue-up. Add-layers, make-work recycled doors, egg carton material filled foam board, all this stuff has been tried for decades in pro shops around the world. They work fine for table tops. They fail utterly for reference surfaes.

Use a traditional built-up core with patina rolled MDF. If you have not seen or heard of patina rolled MDF, call your local sheet goods supplier. Don't bother with Home Depot or the rest of those sorts of places. Go to a professional supply house. The core can be anything with the exact "coeficient" (spelling?) of expansion as the surface. I can't figure that bit out so I use the same product for core and surface.

If you want to use "torsion boxes" for table tops that is great. Don't confuse the two uses. Assembly and glue-up reference tables are not the same as the places you stack your stuff.


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## Kathy36 (Feb 13, 2010)

Hi Bill and Spindrift, Thank you both so very much for explaining both ways of accomplishing my task at hand. Bill, Its always a pleasure for your input. Spindrift, You just needed one more f (coefficient) "who cares, I don't" I appreciate your help. 
Kathy


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## Russ (Feb 19, 2010)

Hi Kathy, How's your top? I just had a thought, if you are going to have the two. Why not make them the same size, this way you can put them together for one big one if you need it. Russ and Jill


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## woodnthings (Jan 24, 2009)

*Flat is relative*

There is "flat", "pretty flat", "dead flat", "absolute flat" and "flat enough"
If you build a torsion box as explained in the video above you are counting on a series of leveling processes and sighting across winding sticks to get a level and flat surface to build it on. This will be "flat enough" but not "dead flat". A friend uses a cast iron dual shaper table as a glue up assembly table 4' x 8' sort of like a surface plate, but much cheaper. If you can build a table that is flat to within a few thousands on an inch, that should be "flat enough" for woodworking. But you will need sophisticated measuring tools to determine that. If you want to build a torsion box, then build one, and it should be a great project. 
As I said aways back, a solid core door covered with MDF will work for all but the most exacting woodworking projects as it can be leveled and shimmed to a "flat enought". If you want to just buy something at a reasonable cost that will give you a "pretty flat" working surface that's what I recommend. 
I also have a hard maple laminate of 1 1/2" x 3" stock 36" x 80".
Epoxy glue used and assembled on the cast iron table mention above, then run through a wide belt sander for final surfacing. 
Very nice, very flat, very heavy, very stable, and very pretty. I don't use it that much though.....:blink: bill


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## Kathy36 (Feb 13, 2010)

Hi Russ and beautiful Jill, I love how you made my top feel and look after you were finished yesterday. I think your idea is excellent! Let me know when you have time to do it again. Same conditions will apply. 
Thank you and everyone else that has helped me with my first project. May all of you great woodworkers out there have your dreams fulfilled throughout your life! I'm so excited "I love woodworking talk. com"
Kathy


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## garryswf (Aug 17, 2009)

We would like to see some pictures of your first project, we like to have our members post pictures of their projects! especially beginners.


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## Kathy36 (Feb 13, 2010)

Hi Garryswf, Would you like to see pictures as I'm progressing along or wait until I'm finished? This really makes me feel welcomed here. 
Thank You! 
Kathy


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## woodnthings (Jan 24, 2009)

*Yes, Pictues by all means, step by step!*

Here's an explanation of why a torsion box works so well from Fine Wood Working. I was going to post my explanation, but this does it much better. Basically the strength comes from separating two planes, top and bottom, with a much lighter, thinner grid. Its like a bunch of "I" beams, where a load on top puts the top web in compression and the bottom web in tension. The vertical member is much thinner than the top or bottom. Here's the link: http://www.finewoodworking.com/Community/QADetail.aspx?id=26506
Racking or twisting of the structure is also prevented by the grid depth.
The glue or adhesive must not fail on the grid to surfaces or the entire structure will fail. :thumbdown: bill


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## Kathy36 (Feb 13, 2010)

Hi Bill, Thank you for all your help and time! I haven't had time to put the hardwood band around my top yet but at least you will be able to see the grid work and the ply's. Sandy and I will be gone for a few days (business, what a drag) and I don't want anyone to think were ignoring them by not posting back.
We will be flying high in the sky and waving hi, to all you wonderful woodworkers out there. I will be sending more pictures as I progress. (until you tell me to stop) Thank you again and I hope you enjoy the other pictures too.
Kathy and Sandy


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## woodnthings (Jan 24, 2009)

*Looks Great*

You're welcome!
Nice job on the torsion box. How did you secure the small lengths to the longer ones? I see glue or adhesive on the tops of all, which indicates you about to put the top piece on. How did you press it down? 
The other shots are cool. Are you in the waterfall one on a photo shoot, the tall one or the shorter one? Is the other photo your house? Where are the palm trees? :laughing: bill


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## SeeDBee (Oct 27, 2008)

Very impressive.


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## Kathy36 (Feb 13, 2010)

Hi Bill and all, I'll be happy to explain my whole procedure step by step. I may not use the same wording as you would but I'll do my best. I'll try not to be too boring! ( ha ha that will be the day) I had some help from another member (Russ) and of course a lot of help from this forum but for the most part I did the work myself. 1) Leveled the saw horses per video. 2) Cut and assembled the frame 84" x 42". 3) Attached the frame to top ply with glue and finish nails. (paslode finish gun) 4) Cut 17 long grid pieces and 136 short grid pieces. 5) I started at one end by installing short and long pieces with glue and finish nails.( I put some nails in at an angle) This was a lot of work but it was Fun! 6) With Russ's help we marked the location of the grids on the bottom ply, applied glue and laid it on the grids and nailed it down with finish nails. 7) Russ laid sheets of plywood on the top for weight while the glue dried. 8) We trimmed the plywood with a router and a flush trimming bit. Among other tools, this was the first time I used a router! All I can say is thank you again to this forum and if I can make this project anyone can! Thank you for your comment Seedbee. Bill, As far as the other pictures. The waterfall was taken a while ago and the blonde could be me or could be Sandy. Who do you choose? The other picture is what I'm having copied for my home this spring. (can't wait!) 
Kathy


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## woodnthings (Jan 24, 2009)

*Kathy that is a "trick" question*

and I don't think I should choose...I'll probably be wrong! :laughing: Besides I'd need a closeup photo...how about it? :icon_smile: I can't be the only one here that would like to see that. :no: bill


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## Kathy36 (Feb 13, 2010)

Hi Bill, You make me laugh with all those little faces! I think I better stay a little bit mysterious for now. Maybe you should create a new post " Do you want to see what Kathy36 looks like? yes or no" Just kidding ha ha! Ok now down to business. Were my step by step instructions correct? Don't be afraid to tell me if I made a mistake. 
Kathy


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## Kathy36 (Feb 13, 2010)

Thank you all very much. This was the start of my first project and with your help I completed my torsion grid top. Now I will be moving on to the cabinets for the base and I hope can rely on your expertise again.
Kathy


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## jlhaslip (Jan 16, 2010)

nice joints, but I'll bet you've heard that before... :lol:


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## TorsionBoxDoorGuy (Dec 18, 2012)

You have different options based on the thickness of your skin. If you really want to keep the wieght low withough sacrificing strength then you should use a thin skin (1/8" ply) with 2"x2" or 3"x3" grids. This is almost impossible to do by hand for big doors. If you Google image search 'honey comb door' or 'honeycomb furniture' there are several patented methods for building this torsion box fast and affordable. If they can make furniture then you should be able to build whatever you need affordably.


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