Torsion Box: Am I doing it right? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 18 Old 07-29-2013, 12:39 AM Thread Starter
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Torsion Box: Am I doing it right?

I need to build a 9' x 3' table that can support a selves filled with gear and tools, as well as leave enough space underneath for a couch to slide under. I designed a torsion box that looks pretty good on paper, but now I'm starting to question the design and stability of the box. Could I get a second opinion and see if there's any major flaws?

The outer frame is built with 1x4 pine and the inner structure along with the skins are 1/2 MDF. I'm wondering if I can use 1/4 MDF for the top and bottom to lighten the weight of the table without compromising the strength.

Torsion Box: Am I doing it right?-cm-capture-8.jpg

Torsion Box: Am I doing it right?-cm-capture-7.jpg

Torsion Box: Am I doing it right?-cm-capture-5.jpg

Torsion Box: Am I doing it right?-cm-capture-2-22-47-33.jpg

Torsion Box: Am I doing it right?-cm-capture-9.jpg
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post #2 of 18 Old 07-29-2013, 08:49 AM
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The 1x4 pine won't support the weight for a table that long. It will need center legs or incorporate steel in the construction of the torsion box. You could make it out of steel and laminate wood over the steel for aesthetics.
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post #3 of 18 Old 07-29-2013, 09:54 PM
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More than just that, the connection of the legs is really weak You are asking those two small pins to carry all of the weight down thru the leg. Even if the pins were made out of steel, the load could possibly tear through the hole in the wood that they sit in. I advise that you rethink your method of leg attachment. I would suggest making either an L bracket out of plywood or a u channel that spans the entire length of the table an have the leg rest inside the channel or bracket. Cross brace the legs so that they don't rack as well.


Last edited by chopnhack; 07-29-2013 at 10:05 PM.
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post #4 of 18 Old 07-30-2013, 12:22 AM Thread Starter
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8 steel L Brackets seem like a pretty easy fix. I'm trying to keep the design as slim as possible. I'm wondering if there is a way to not show them.
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post #5 of 18 Old 07-30-2013, 09:46 AM
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you can't assemble this joint

it won't go together, unless the holes go all the way through and the pin or dowel is driven in from the outside.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 07-30-2013 at 10:04 AM.
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post #6 of 18 Old 07-30-2013, 10:02 AM
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there are different ways to brace the legs

here's some corner braces;
http://images.search.yahoo.com/searc...r+leg+brackets

Your issue is the that there is no or little access on the inside of the the structure to fasten the legs. Imagine a hollow corn door with legs "attached" at the 4 corners....not a very strong structure. The deeper your torsion box is the better the leg attachment will be, but your design call for a thin, light weight table, with the legs flush at the corners. It's a difficult challenge to meet all the criteria. At a minimum I would double all the internal pieces which meet at the corner. Then you can use lag bolts with counterbores to attach the legs... and glue and then plug the counterbore holes.


Your other issue is that this table is HUGE, 9 ft long. and you don't show any shelf details or locations .... "and space underneath for a couch to slide in"...?

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 07-30-2013 at 10:06 AM.
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post #7 of 18 Old 07-30-2013, 10:32 AM
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For that length, I would double up the rails like the sketch below. Doubled up rails like that along the center would carry more weight. I would use stock more substantial than Pine.
.
Torsion Box: Am I doing it right?-support-rail.jpg









.
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post #8 of 18 Old 07-30-2013, 12:51 PM
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Can someone tell me what a torsion box is/does?
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post #9 of 18 Old 07-30-2013, 01:05 PM
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Quote:
Originally Posted by Bastien View Post
Can someone tell me what a torsion box is/does?
The eggcrate design is supposed to make a stiff shelf, or top, that resists deflection.






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post #10 of 18 Old 07-30-2013, 01:13 PM
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Thanks
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post #11 of 18 Old 07-30-2013, 02:04 PM
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a torsion box build shown here

http://www.woodworkingtalk.com/f2/to...rniture-49361/

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #12 of 18 Old 07-30-2013, 06:50 PM Thread Starter
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Ok. Everyone is in agreement that pine is a terrible idea. I found a lumber yard that sells 4x10 sheets of 1/2 MDF so all the components will be made from the same sheet. I reinforced the legs from two sides with 1 1/2'' hardwood and drilled at 6'' bolt through both sides of the leg, plugging the hole with a 3/4 dowel. The Bolts can be accessed from below the table through a little 1'' opening in the underbelly. I also added support to the legs...... safer?
Torsion Box: Am I doing it right?-cm-capture-3.jpg

Torsion Box: Am I doing it right?-cm-capture-2.jpg

Torsion Box: Am I doing it right?-cm-capture-1.jpg

Torsion Box: Am I doing it right?-cm-capture-9.jpg

Torsion Box: Am I doing it right?-cm-capture-11.jpg

Last edited by Helloooo; 07-30-2013 at 07:03 PM.
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post #13 of 18 Old 07-30-2013, 06:57 PM Thread Starter
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the final design should look something like this. Torsion Box: Am I doing it right?-cm-capture-5.jpg
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post #14 of 18 Old 07-30-2013, 09:53 PM
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Much better! Now when you tire of assembling you can nap next to your work and watch the glue dry
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post #15 of 18 Old 07-30-2013, 10:51 PM
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the whole and the sum of it's parts

By combining the shelves and the table into one structure, less strength will be needed in the table IF you but a back in the shelfe unit and secure the 2 pieces together.

If the shelves are open then, this doesn't apply. Why? A sheet of plywood secured in the vertical position has incredible resistance to bending.The "egg crate" design of the shelves makes it rigid and when you tie it to the table top it becomes a stiffener for the top.

I don't understand the reason for "hiding" the couch, unless the room is 6 X 10 ft. and space is severely limited. If it were me and I wanted a bunk to sleep on and a storage above, I'd ditch the couch and make a platform bed with pull out drawers for storage underneath. OR I'd make the bed above the whole unit and use a ladder to climb up there. I had a bed like that in college with a small workshop below on 4 x 4 posts but we had 10 ft ceilings in an old house in Chicago.


The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #16 of 18 Old 07-30-2013, 11:17 PM Thread Starter
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Alright it's on!

The desk will be built behind a seamless backdrop in my studio/living room. All my photo equipment will be stashed behind the 9' backdrop along with the couch during a shoot. At night, I'll rearrange the furniture and have a normal living room setup again.

You have to get clever in NYC. Plus I don't have a car or workshop so everything has to be planned out perfectly before I can even buy wood, rent a car, chop the pieces, load the car, and walk up stairs
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post #17 of 18 Old 08-01-2013, 10:12 PM
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Quote:
Originally Posted by Helloooo View Post
Alright it's on!

The desk will be built behind a seamless backdrop in my studio/living room. All my photo equipment will be stashed behind the 9' backdrop along with the couch during a shoot. At night, I'll rearrange the furniture and have a normal living room setup again.

You have to get clever in NYC. Plus I don't have a car or workshop so everything has to be planned out perfectly before I can even buy wood, rent a car, chop the pieces, load the car, and walk up stairs
You have my sympathies. I used to live in one of the boroughs. Now, I only have to suffer the removal of the kids car seats from the minivan when I want to get some lumber or ply home.
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post #18 of 18 Old 08-01-2013, 11:12 PM
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I do love my Midwest. I feel for you big city guys...

The tools don't make the craftsman....
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