Hidden Bookcase Door

[bobgaggle]

So this isn't really scenery, but my woodworker father in law is building a hidden door bookcase and is running into some trouble. I figured maybe some theater people would have a fresh perspective...

The case is 46"w x 81"h x 10"d. It hinges on Rixon pivot type hinges at the top and bottom, http://www.rixson.com/pivottypes/, and swings into the room (or i guess downstage if this was in a theater haha) The issue he's having is that the case (which is 3/4" ply construction with a 1/2" ply back) is warping under its own weight and isn't sitting flush with the wall when its closed. The top corner is leaning into the room while the bottom is flush with the wall. He was contemplating added a 3/4" ply sheet to the back to stiffen the whole thing, but I feel like he'd still have the same problem.

My solution is to weld up a 1x1 16ga. steel tube frame that will get screwed onto the back. I'm not an engineer but I feel like it'll be stiffer and weigh less than a 3/4" sheet. I figure standard steel flat construction with three toggles. I may be getting too clever for my own good, but my thought was that as I weld it flat on a table, I'll shim up one corner an inch or two and leave the rest on the same plane, building it intentionally warped in the opposite direction that the case is. When the frame gets screwed to the back of the case, it'll twist and provide some spring tension to pull that corner of the case back. Some moulding acts as a stop to keep the door from overswinging and to conceal the seam.

Any other ideas? He's already tried an aircraft cable and turn buckle across the back (like on a screen door) but it didn't help at all. Is another sheet of ply the way to go?

 

[manuallyfocused]

He could try a piece of plywood warped in the opposite direction, or the steel frame as you suggested (though if the weight is enough, over time either solution will likely still lean into the room). What about putting a fixed wheel or two under the edge of the bookcase that swings into the room? Of course this will depend on the floor material and would be a poor choice for carpet or other soft flooring, and may still dig a channel into the floor if there isn't a way to put some kind of metal track in for it to ride on.

Is the hidden door going into another room? What about a curved metal arm sticking out from the top of the unit with a decorative counterweight? Or a counterweight hidden in the wall and attached with a cable to the back of the protruding part? This would have the added bonus of making the bookcase self-closing.

 

[JChenault]

this is a really heavy door, but the direction of warp as you have described it does not make sense to me. IE as I am reading it, if you put a level in the hinge side of the bookcase, it would be vertical, but when you put a level on the opposite side it leans toward you.

I can understand a stress on the bookcase that would try to take it out of square, but you are implying it is square, but is warping forward at the top.

Are you sure that the frame is square?
Are you sure that the bookcase was not built inherently crooked? ( IE take it down, bought it on a flat surface. Does it sit absolutely flat? Stand it up with no hinges sitting on the door. Is it still flat?
Are you sure the hinges are placed absolutely correctly?


I would check these first.

 

[venuetech]

I would build the back like a torsion box

 

[bobgaggle]

this is a really heavy door, but the direction of warp as you have described it does not make sense to me. IE as I am reading it, if you put a level in the hinge side of the bookcase, it would be vertical, but when you put a level on the opposite side it leans toward you.

I can understand a stress on the bookcase that would try to take it out of square, but you are implying it is square, but is warping forward at the top.

Are you sure that the frame is square?
Are you sure that the bookcase was not built inherently crooked? ( IE take it down, bought it on a flat surface. Does it sit absolutely flat? Stand it up with no hinges sitting on the door. Is it still flat?
Are you sure the hinges are placed absolutely correctly?


I would check these first.

its square, the 1/2 ply is doing a good job keeping it from racking, i think the structure is just wobbly, meaning if I lay it flat as you described, I could lift up one corner about an inch while the rest stays on the floor. Its doesn't have much torsion strength.

 

[sk8rsdad]

Try putting a set of casters under the floating end to take the weight. At least a pair would be needed to deal with the depth.

 

[kicknargel]

If I'm understanding the geometry right ( a drawing would help), it seems the problem is not so much the stiffness of the back panel as the sides. You want to look at the plane that is parallel to the direction of the warp. Can you stiffen the outer perimeter (essentially the 10" deep perimeter frame)? Maybe even a 10" deep steel plate across the top of the bookcase would keep the top corner opposite the hinges from being able to bend forward.

 

[JChenault]

its square, the 1/2 ply is doing a good job keeping it from racking, i think the structure is just wobbly, meaning if I lay it flat as you described, I could lift up one corner about an inch while the rest stays on the floor. Its doesn't have much torsion strength.

Humm

So if you picked up the corner an inch. Where is it coming from?

Are the joints between the 3/4 frame not tight?
Is the 3/4 frame warping / twisting some how?

A thought just occured to me. Are there shelves in the book case and are they glued and fastened to the frame? If not I expect that this might stiffen the structure substantially.

 

[Christopher L Jahn]

...Any other ideas? He's already tried an aircraft cable and turn buckle across the back (like on a screen door) but it didn't help at all. Is another sheet of ply the way to go?

When I've built them, I've always had the end opposite of the hinges ride on wheels. If I use a center pivot, then both ends have casters to support the load.

 

[bobgaggle]

The shelves were adjustable, the first thing he did was glue them in...no luck. A wheel towards the front of the case might have worked, but the case floats about 3" above the floor when its open. (it swings over the permanent baseboard so you have to step up over the ''thresh hold")

 

[bobgaggle]

update: I made up a steel frame without the warp in it. It pulled the door back a little bit and helped with the racking. We ended up putting a shim of uhmw under the front end to force it up a little bit, closing the gap at the top. The added friction also helped keep it from slamming shut if you closed it too fast. I'll try to get a video linked, I'm pretty happy with how it turned out

 

[bobgaggle]

Heres a link

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