How do I prevent doors on a media cabinet from sagging?

Question

A friend and I have just built a floor to ceiling media shelf unit for DVDs. It has 9 shelves and is about 3' wide. The frame around it is made up of 2"x8" boards and the shelves (except for one in the middle) are all 1"x8" boards. At the bottom there's a 2"x12" that provides a lip and the front is cut on an angle going toward the floor at the very front.

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I didn't know if I'd have to add doors or not, but now it's clear I will. These doors would be from 6"-8" thick, with shelves in them, so they can hold more DVDs and blu-ray discs. Basically, I want doors like in the last picture below. It'd be two doors, each half the width of the shelves (so that'd be about 18"). Since this unit is about 8' high, I'm also splitting the doors vertically, to limit the total weight put on any door.

When doors are closed, they will rest on the lip. (That's the purpose of the 2x12 at the bottom - provide support for the doors full of DVDs when the door is closed, as they usually will be.)

But this is a fair amount of weight. I know I can use strong hinges and even extra hinges to keep the doors on, but my concern is about the doors sagging over time. I don't want to add a lot of weight. In my head, I'm picturing a sheet of plywood (1/8" thick) and 1x6 or 1x8 boards mounted on that, to make the frame and shelves for the door.

But I've never done a project quite like this and I want to make sure there is no sag from the side of the doors on the hinges on the edge, and the other side of the doors, in the middle.

Will plywood be enough to keep the frame from sagging or changing shape, or do I need to do more?

NOTES:

1. After a few comments, let me add that the door on the upper right will be shorter than the door on the upper left, due to the door arch, and we talked about adding another shelf running over the door to make up for the lost shelf space.
2. The shelf unit is attached to the studs in the wall with screws, so I'm not worried about the balance or tipping issue.

Answer 1

Plywood will not sag over time if you intend to use it for the door faces. I recommend birch plywood for not only its hardness but looks. However your hinges and what they are attached to are the big concern in this project. It looks like you've used a low grade pine to build the unit. This is a soft wood and a couple of cabinet hinges screwed into this are going to loosen quickly. Your best chance for longevity is to use a piano hinge so that you have a continuous hinge from top to bottom with 15 screws or more on each hinge. I highly recommend ordering a stainless steel or flat nickel piano hinge for this. What they have in stock at the box stores is of the "bright" variety and looks cheap to me.

I'd also recommend that you not attempt to build the door to be perfectly flush with the "lip" at the bottom. Leave yourself 1/4 of an inch gap. Units like these always sag at least to some degree and you wind up with the door scratching the "lip" and its going to look really bad with time.

Also take a look at ball catches to use either at the top or bottom of the doors to hold them in place once closed.

Answer 2

Pivot hinges would be an economical solution for good weight bearing. You have to provide a solid top pivot point.

This Stanley has 150 lbs capacity. There are many others of this type, ranging up to 1000 lbs.

Used by all secret bookcase doors.

Answer 3

Ply is good in shear, helping the door from racking.

I would use euro style hinges, meant for frameless cabinets. They will transfer the door weight better than simple butt hinges. They also have 3 way adjustments for compensating for sagging over time. Just be sure to start out with a good gap and room for the hinge to adjust up.

Answer 4

I think plywood would make a good backing for the doors. I would use something with better quality though and not 1/8 " thin junk or "masonite" type products. My take would be to use two layers of 1/4 inch material. One layer can be screwed through the face into the shelves to make a very sturdy structure. The other can then be glued to the first with the nice finish side facing out so as to get a nice look without any fasteners showing.

You will want to use very sturdy hinges. Stay away from cheap cabinet or gadget type hinges. Instead use some hinges designed to carry a big load similar to what you might find for full sized entry doors such as 4" size using longer than normal screws.

I do see a problem of how the door on the right side of your shelf would open.

A pictorial diagram looking down from the top of your unit with its door shelves attached should reveal the problem.

A final comment is to make sure to fasten the existing shelf unit into the wall to keep it from tipping forward when the heavy doors are open.

Answer 5

I'm curious to know how much a door full of DVDs would weight. I calculate about 60lbs for 9 shelves with 15" inches of DVDs per shelf, 2 DVDs per inch, and .21 lbs per DVD (3.2 oz). And then the weight of door+shelving itself.

There are no cabinet hinges of any design that I know of that will carry that weight. Even half that total weight, say 30lbs DVD plus 20lb door+shelving will be huge for hinges that are design to carry only a couple pounds. I've only ever seen kitchen cabinetry with pull out racks for canned goods. Anyway, I'm probably wrong on this. There probably are cabinet hinges made with a high load rating. As an alternative, premium quality heavy duty hinges on used commercial grade doors can be found at places like HH's Restore. I'd either just buy the door ($15, great work bench) or ask to buy just the hinges.

With well attached plywood back on the DVD case, even a 1/8" plywood back, or a masonite back, I do not think any problems at all will arise with the door sagging, per se. Instead, the weight of the loaded door will cause the door to twist. Locating the hinges so that the hinge pins are in the middle of the 2x8 edge of the door would reduce but not eliminate twisting due to the load. When open, the loaded doors will also cause the top corners of the fixed case (which looks awesome by the way!) to pull away from the wall, possibly tipping over ... if they are free standing.

To carry the weight, I'd think about using a spring-loaded wheel underneath (the existing 2x12 seems to leave room for the wheel to always be in contact with the floor). For the closed position, I'd think about a nylon glide to the bottom of the door and another to the top of existing 2x12.

Alternatively, I'd consider a semi-circular track mounted on the ceiling, possibly inlaid, or partially inlaid into the ceiling finish. The track would capture a wheel on a shaft, the shaft attached to the top of the door.

Alternatively, I'd consider building a single 36" wide door to slide to the left. When loaded with DVDs, it would weigh about 150 lbs. A left sliding door would also solve the issue of the doorway header on the right. An 8-shelf door would another work-around for the that issue.

I think the main issue in using kiln-dried two-by stock for the doors will be it developing a twist due not to the DVD load, but due to the two-by stock settling out it's tension. Sugar pine, is super stable and available in your required dimensions. Yikes on the price though. I've used it to build mortise and tenon 9-ft exterior doors with true divided lites, 42" wide, out of sugar pine that are still flat now going on 24 years.

Answer 6

I don't think splitting the doors vertically will make any difference: you'll be cutting the load in half, but also cutting in half the amount of support and the number of hinges. I wouldn't bother.

By the way, you should be careful about the balance of the shelf. If sounds like you're going to be filling the door shelves with DVDs just like the main shelves. That means they're going to have roughly the same amount of weight in them, and you'll be risking the shelf tipping when you open both doors at once.