Torsion box assembly table - UPDATED

[bobby g]

The assembly table in my shop is my favorite place to do just about anything but it has developed an annoying sag. After months of shimming temporary additional tops, I decided to stop and build a flat table top that will stay flat. I watched the David Marks program on the torsion box and set out on Friday to build one. The first step was to purchase the MDF that was needed. Due to having had bad luck with Chinese plywood and not being able to determine the origin of the big box MDF, I headed to The Hardwood Store in Gibsonville to purchase some good, made in the USA product. I found out that they too will do a few free cuts!

Yesterday, I spent the afternoon preparing a flat surface on which to build the flat surface. This consisted of milling 5 - 2X4's, placing them on top of the sagging table and shimming them untill the top edges were all in the same plane. Per David Marks' suggestion I layed 2 sheets of MDF on top of them.

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Next, after ripping a lot of MDF, it was time to start the assembly. Glue and brad nail, glue and brad nail, glue and brad nail, etc. (Bas would enjoy this project).

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and more

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and more

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and finally... :banana:

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This evening I layed a piece of 1/2" MDF on the grid and checked it out for flatness and it was pretty darn good. Quantitative data coming soon. I've got to hurry up and get it done in the morning because all of that weight is making my old top sag even more! :icon_scra

Thanks for looking.

bobby g


Added more photos today (08-18-2010) :icon_thum

 

[eyekode]

Re: Torsion box assembly table - WIP

Looks good Bobby! I bet it weigh's a ton. What is that 3 whole sheets of 1/2" MDF?

Also wondering how you fired your brads. Are these just toe nailed? 1/2" MDF usually does not take kindly to toe nailing .

 

[bobby g]

Re: Torsion box assembly table - WIP

Looks good Bobby! I bet it weigh's a ton. What is that 3 whole sheets of 1/2" MDF?

It will take about 3 whole sheets of 1/2" plus the outside band is 3/4". The final weight will be around 220#.

Also wondering how you fired your brads. Are these just toe nailed? 1/2" MDF usually does not take kindly to toe nailing .

From one side it's straight nailed and from the other it is toe-nailed. On toe-nailling, keeping the nail from popping out the side is somewhat of a trick but it really doesn't matter much after the glue has dried. On the straight nailing, the distance from the edge of what you are nailing into is important in addition to nail length.

regards,
bobby g

 

[Bas]

Re: Torsion box assembly table - WIP

Wow! A Texas-sized Belgian waffle maker!

Looks great Bobby, that is going to be a very stable assembly table when it's done. This is another one of those projects on my list, although I'll probably limit my table to 5x4. As for enjoying firing all those brads....yeah....fun.....

Did you joint the 2x4s, or only shim them?

 

[Bas]

Re: Torsion box assembly table - WIP

I'm wondering if it's feasible to build a table this way, but have the edge be 3/16" higher than the top sheet of MDF that covers the grid, and then pour an epoxy finish on top. Self-leveling AND protection layer in one step. Of course, your table has to be 99% flat to begin with.

 

[bobby g]

Re: Torsion box assembly table - WIP

Wow! A Texas-sized Belgian waffle maker!


Did you joint the 2x4s, or only shim them?

I jointed them and then planed the other edge parallel. It took a lot of time to get the shimming just right.. to avoid making a seemingly flat but somewhat twisted surface, for example. Learned lots of new trivia - Post-it notes are .004" thick, playing cards are .011", hotel key cards are .039". I ended up using winding sticks to check it for the final time.

bobby g

 

[Alan in Little Washington]

Re: Torsion box assembly table - WIP

I'm wondering if it's feasible to build a table this way, but have the edge be 3/16" higher than the top sheet of MDF that covers the grid, and then pour an epoxy finish on top. Self-leveling AND protection layer in one step. Of course, your table has to be 99% flat to begin with.

You could build it then add 1/2" hardwood sides that are 3/16 taller, but epoxy (or other self-leveling material like cement) would probably be too brittle and crack the first time you torqued a clamp on it. Flatness is only relative- you are doing woodworking not lapping the mirror for a space telescope. You are right- to make a flat table you need a flat construction platform. I found David Marks' method and using winding sticks quite acceptable.

FYI, the brads David Marks uses only hold the pieces together for assembly, they add almost no strength to the torsion box. I only used brads to attach he sides and the top. I found it much easier and quicker to assemble the grid by using a dado blade and simple a box joint like jig to cut halved joints in the full size grid pieces.

If you have the room in your shop, a good, flat assembly table is indispensable.

 

[bobby g]

Well, It's just about finished.

This photo shows a close up of one of the runners that I used to help get the MDF in position after the glue was applied. These hold the MDF 1/2" above the grid.

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Here is a full view of the setup.

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Here is the new top in place on the old table base.

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I'm going to add a sheet of 1/4" hardboard as the working surface, held in place with a few brads, that can be replaced if needed. Then, I'm going to band it with white oak that I harvested during the house and shop construction.

Seems to be flat enough for government work. It's generally within .010". I don't know the thickness tolerance of the MDF. Now that I have a flat surfce to reference from, the next one ought to be easier to build.

Thanks for looking,

bobby g

 

[Charlie]

Bobby, Very nice job. It is so much easier to build things straight/square when you have a flat surface to start from.

 

[Bas]

Now that I have a flat surfce to reference from, the next one ought to be easier to build.

You heard the man - torsion box assembly table group build in Bobby's shop this fall :gar-La; :gar-La; His shop is big definitely enough for 8-10 assembly tables.

Thanks for the detailed pictures.

 

[MarkE]

Excellent job. Thanks for all the pictures.