Shop door design questions

Hi all!
I'm about to build 2 swing out shop doors to replace a 10' wide roll up door. I'm going to build torsion box style doors to save on weight but still have the strength I want. a couple questions. Since the doors will be almost 5' wide, and about 88" tall, what is the best way to route the webbing? Just straight across, or do it on a diagonal for strength to help prevent sagging? Any one know where I can buy tamper proof hinges for this weight of doors? I have had some good ideas from another thread on the woodworking forum a few weeks ago, but if anyone has any other ideas I'd like to hear them. I plan on using 1/2" plywood for the webbing, 3/8" ply for the skin. What type of wood should I use for the edging, just standard 2X4..yellow pine or white wood? Anything else you can think of that I'll need? Thanks for your help and ideas! Jim.

A thought for you. I just picked up Scott Landis' book on workshops that had a very interesting door featured in it.

It was torsion box construction too. The feature was that it had another door in the big door for normal egress. The big door would open and close like you would expect it to do, and was very well insulated, using "cam locks" to make the weather strip seal correctly. The hinges were heavy duty strap hinges (no removable pin). The little door was hung the same as you would hang one in a wall.

Yes, I've even seen a normal egress door in a roll up door before. Of course the door has to be in the down position to work, but it did work. I'm not concerned about an egress door here. I'll enter and exit through the door to the back yard, and have these open when weather permits or I need to move large objects in and out. I'm not even going to put any windows in these doors. Thanks Hal. Jim.

From my knowledge of torsion boxes, the strength comes from the glue to skin bond. Having said that, I don't really know if the direction of the webbing will have as much to do with it as the glue area. A square grid will be a whole lot simpler to cut and fit than angled corners for the diagonal.

Jim --

Like Hal says, the direction of the spacer grid doesn't affect the stiffness of the torsion box. The spacer grid just holds the skins apart, and the strength comes from skins.

For really wide doors like you're planning, you might consider using door pivots instead of hinges. Hinges hang all the weight and leverage of the door off the jambs and wall framing. The door tries to rip out hinge screws, and bend the wall. Door pivots are most often seen on big doors in commercial environments, and carry the weight of the door directly to the floor. The big dog in pivots is Rixson. They have an informative web site at http://www.rixson.com/. There are also other suppliers; google with "door pivot".

Jamie, that is excellent information. THANKS!! That looks like the way to go! Jim.

John Lucas at workshopdemos built some for his new shop. He has a very detailed tutorial on his website.

Thanks Chris, I'll look at his site tonight when I get home. Jim.

[QUOTE=Jamie Buxton]Jim --

Like Hal says, the direction of the spacer grid doesn't affect the stiffness of the torsion box. The spacer grid just holds the skins apart, and the strength comes from skins.

Jim,


A torsion box works much like any sandwinch structure. It is a structure made up of two strong, thin facing outer layers and a core. Torsion boxes typically have thin wood grids as a core but I have also seen 2" foam cores used on larger shop/barn doors with great success. The doors success will greatly depend on the adhesive used to join the different materials together.


The purpose of this type of construction is to increase the rigidity of a panel by increasing its thickness with relatively little increase in weight. Sandwich panels function similar to an I-beam in that greater structural efficiency is achieved by placing the material further from the neutral axis.


The outer facings take up in-plane stresses while the core takes up shear forces and stabilizes the facings from buckling. A sandwich construction distributes stresses over a much greater area resulting in a structure of uniform strength with no stress concentrations. In general, a composite sandwich structure will be lighter and greater flexural rigidity.


For external hinges, the inner "core" could be altered slightly to accomodate solid blocking the help distribute the load.

Cheers,

KP