I am building a cabinet that will house a slide-out AV rack and a mini-fridge. The outter dimensions are set in stone and to make sure I have enough room inside it I need to keep the inside as wide as possible.

I did this model in SketchUp, I was hoping someone could comment on the cabinet and if it would be strong enough considering there are no bracing along the front or across the sides to save space. The framing is 2x4 and the cladding is 1/2" MDF.
http://xraycat.homeserver.com/photos/cabinet1.jpg

This is with the AV rack and fridge:
http://xraycat.homeserver.com/photos/cabinet2.jpg

Looks like you have about a 19 1/2" span for the shelves in your AV rack. I think your biggest concern is going to be shelf weight limits, and adequately supporting your equipment.

MDF is notoriously poor at supporting weight and can sag visibly. Based on a 24" span and 11" depth, 3/4" MDF can support 9 pounds per foot. So your receiver is likely going to put quite a strain on an MDF shelf.

That being said, it looks like you have some decent reinforcement planned there with the triangular braces (are you using metal braces?), and the weight of the receiver is often at the edges of the shelf, as opposed to a collection of books that would put more stress on the middle of the shelf.

I'd make sure to use some sturdy bracing for the shelves, not just 1/2" MDF facing. And don't skimp on shelf supports. You may want to consider plywood for your shelves, and even adding some hardwood (e.g. 1" banding) to strengthen them. I'd also add another 2x4 piece in the middle bottom to support the weight of the fridge.

Hope that helps.

Awesome comments. I will definitely make the shelves out of plywood then - should I use 1/2" or 3/4" plywood?

I was going to be framing the AV rack with 1x2 lumber and 1/2" MDF for the top and bottom, I guess I forgot to indicate that on the drawing. I have been considering metal but I think I may stick with wood for the whole thing, although metal for the angle braces is probably a good idea.

What about the cabinet, does it seem to be fine? I will also add another 2x4 to span the middle of the bottom, that makes a lot of sense.

I have indicated what materials I'd be using by textures. The stuff that looks like OSB will actually be MDF or particleboard. The shelf brackets and diagonal braces are metal. The 2x4 and 1x2 are lumber.
http://xraycat.homeserver.com/photos/cabinet3.jpghttp://xraycat.homeserver.com/photos/cabinet4.jpg

You'll probably get some value from reading this thread:

http://www.digitalhome.ca/forum/showthread.php?t=101172

ya i've read that thread a few times, i'm more or less basing my shelves off of what he did. I may even take the final step and see if I can make the faceplates for my equipment too.

The biggest difference is that my rack will slide in and out because I won't have access to the rear of the equipment with it being in the cabinet. I will just need to find the same kind of shelf rails and brackets so that they are strong enough to hold the equipment on 3/4" plywood. I'm not as concerned about using moulding either though but I may do it once everything is built.

WRT preventing any chance of the MDF sagging:

I used 3/4" MDF extensively in a library I built about 5 years ago. To ensure that the weight of books didn't cause the shelves to sag I used 1/2" right-angle aluminum glued along the front edge - it tidies up the MDF edging nicely, it holds paint very well, it protects the edge of the somewhat vulnerable MDF, it doesn't get dinged....and it doesn't sag!

I've also successfully used 1" birch for MDF shelf facing/banding (also for supporting books) - just make sure that the facing is well glued and nailed so that it becomes a properly integrated part of the shelf (not just a tacked on cosmetic add-on). One benefit of the aluminum is that it doesn't really add anything to the depth of the actual shelf - I couldn't tell if this is a major consideration for you.

As previously mentioned - all of your weight will be along the sides of your MDF shelves, so I don't actually think that sagging will be a major problem for you anyway.

I've also successfully used 1" birch for MDF shelf facing/banding (also for supporting books) - just make sure that the facing is well glued and nailed so that it becomes a properly integrated part of the shelf

My old AV rack did it that way -- MDF shelves with pieces of (I think) pine glued and doweled into the front and back edges. It spanned at last 20 inches and I don't recall it sagging at all. In the case of rygy's design the strip could be designed to fit between the rack rails and bring the face of the shelf flush with the face of the cabinet (which is also what mine did):

http://www.dododge.net/avsforum/shelf-face-edge.jpg