Large Cabinet ????'s

[Chris Lee]

I am in need of some design advice. While the design will be very simple I need to make sure it is sturdy. To stay in shape I take martial arts classes 4 times a week. My instructor just recently opened up a new place locally and he is in need of some cabinets to store weapons and such in to keep them away from the kids.

What he invisions is a 12ft wide x 7ft tall x 1ft deep! I told him we could probably do something 4ft wide and make 3 of them stacked next to each other. He is ok with that idea.

My question is will it be sound? I am thinking a typical box with the sides resting in a rabbit in the top and bottom, and the back sitting in a rabbit going all the way around. The doors will be a solid wood frame as he wants plexi in the doors so he can see everything. The body will be built out of some type of ply, I have not decided yet, something cheap and then all will probably be stained with a black wash or similar to still show the grain.

So does that sound like it will be strong enough, as there is no fixed shelf in the middle, just a big opening as some of the staffs etc. are 6 1/2 ft long.

Any advice you may have as far as fastening or other I would appreciate it.

Thanks,
Chris

[Tim Sproul]

Size the face frame appropriately. Attach the back with more than a few brads...glue a 1/2 inch plywood back on. Fix the cabinets to a subbase and attach to a wall if possible. I'd think about using 2x2 hardwood frames with thinner plywood panels rather than just plywood. The thicker hardwood will let you use longer tenons and that would help fight racking stresses. Corner blocks in discreet places might be called for if you stick with all plywood case.

[Dan Gill]

I first thought of this like it was three bookshelves. But the fixed shelves in a bookshelf give it a lot of resistance to racking, and you won't have that. Still, with a face frame and a 1/2 inch ply back, I think it would be quite sturdy. You might want to consider cleats on the inside, say 3/4 x 2, which are attached to the sides and to the back. That would add a lot of strength and would give you a way to attach hooks, pegs, whatever to help keep the interior organized.

Of course, attaching the whole thing to the wall will make it even more stable. With a 1/2 inch plywood back, you could screw it directly to studs and nothing would move it without moving the wall.

[Jim Becker]

I first thought of this like it was three bookshelves. But the fixed shelves in a bookshelf give it a lot of resistance to racking, and you won't have that.

Modularity combined with a single fixed shelf and a 1/2" back should make the project very stable...and movable. Alternatively, you could put two fixed shelves in; one near the top and one near the bottom, similar to the armoire that I recently built. This would add stiffness while providing organization for smaller items. In fact you could put drawers under the bottom shelf in that latter design, also similar to the armoire, for such storage. Either of these methods would work for both a face-frame design and a frame-less design and give you plenty of stiffness and resistance to racking.

BTW, when you install, absolutely be sure that the top of the cabinets are strapped to the wall to insure they can't be pulled over by people or unbalanced loads inside.

[Chris Lee]

Thanks for all the advice. Still not sure exactly how I will proceed, but I am pretty sure I will be attaching it to the wall.

Thanks,
Chris

[Dan Gill]

Modularity combined with a single fixed shelf and a 1/2" back should make the project very stable...and movable.

That was my first thought, Jim, but he said he had to put 6 1/2 ft. staffs in it. That kind of puts the kibosh on a fixed shelf, unless it's just 6 inches from the top. That's why I thought about cleats on the back as stiffeners. But your advice about attaching it to the wall to avoid tipping was something I missed. Especially in a martial arts studio, where there are bound to be kids just dying to climb, hang from, or swing from anything. It's a kid thing . . .

[Jim Becker]

The 1/2" back should help keep it stiff and if you use a face frame design, that will also contribute additional "stoutness" to the cabinetry. Further, once you lock them together...they ain't going anywhere...

[John Stevens]

If another 2"-3" depth is not a problem, consider torsion boxes for the backs instead of 1/2" ply. More work (perhaps), but it will give you a rock solid "base" from which you can "hang" the rest of the cabinet. Skins can be 1/4" ply with a nice face for the interior. I'd recommend ultralight MDF or ultralight ply for the ribs--stable, but more manageable weight than regular MDF or ply.

Two challenges with making torsion boxes this big are finding or making a flat surface to press/clamp the skins to the ribs, and getting adequate clamping pressure for glue-up.

I made a 4' x 8' torsion box a couple of months ago and spent a lot of time before glue-up making sure I had adequately supported the large areas that overhung the 23" x 78" workbench I was building it on. After you successfully glue on the second skin and the glue cures, you can use the first torsion box as a base for assembling and gluing the other two.

If you use epoxy then clamping pressure isn't a big deal. I used yellow glue because that's what I had on hand, and used ~ 400lb of free-weight plates centered over the ribs to press the parts, because I didn't have a vacuum bag and didn't feel like making clamping cauls for that size. A sheet of 18mm MDF temporarily placed between the top skin and the weights added another 100 lb and distributed the pressure of the wieght plates an extra 3/4 inch beyond their circumferences, which allowed me to space the plates ~ 1 1/2 inches apart. The pressure in terms of lb/sq. in. was not nearly what is recommended, but I haven't had a problem yet.

Gluing the first torsion box "one-skin-at-a-time" will keep things manageable. You may be able to press more than one skin (or one box) at once, although I haven't tried that yet except with smaller torsion boxes (~2'x2').

[jack duren]

Chris... this will be fastened to a way i expect, correct?....jack

[Chris Lee]

What's a way? They will be fastened to the wall. I hope that was what you meant to type or I have to brush up on the lingo!

Chris

[jack duren]

way ..

if they are fastened to the "wall/way" then 1/4 back should be fine. usally the only time a 1/2 or 3/4 back is required is when the unit is free standing or in need of additional shelf support in the middle......jack