Cabinet Design Question

[jackellis]

Some time back Cabinetman wrote:

A question came up about using 1/2" ply for backs to carry weight. Plywood backs of any thickness should be set in a rabbet. For starters, the depth of the rabbet could amount to the thickness of the back. If a 1/4" plywood back is used, a minimum rabbet would be 1/4" x 1/4". The depth into the cabinet could be increased to allow for scribe, or uneven walls. Backs into a rabbet add rigidity to the carcass and can square the cabinet.

I understand why (and I'll remember to do it on the next project), but is there any reason a back fastened flush with either screws or nails wouldn't be suitable for a cabinet that's not hung? This is the same principle that's used when building wood frame homes to provide shear resistance (nail sheathing to the studs) and all I really want to do is stiffen the cabinet a little.

Of course if the answer is no, I could use my router to cut a silly little rabbet in the back I suppose.

[chopnhack]

I believe the reasoning is that you get way more integrity as the piece behaves as a whole with a rabbeted back. Just installing a piece flush will only yield the strength of the fasteners at each location. If you were to hang the piece from the back, the energy would be trasmitted through the nails to the frame whereas in the rabbeted method, the frame hangs from the back piece. Hope this makes sense.

[BobSch]

Take a look at Tom Clark's site for his take on cabinet backs.

http://www.tomclarkbooks.com/tomclar..._Cabinets.html

[cabinetman]

I believe the reasoning is that you get way more integrity as the piece behaves as a whole with a rabbeted back. Just installing a piece flush will only yield the strength of the fasteners at each location. If you were to hang the piece from the back, the energy would be trasmitted through the nails to the frame whereas in the rabbeted method, the frame hangs from the back piece. Hope this makes sense.

This is part of the reason. A rabbeted back is a captive back. It's not only held in with fasteners, but the shoulder of the rabbet provides a guideline for the back. When the back is cut to fit the rabbet, it will square the cabinet. Surface mounted backs attached with just fasteners become subject to torsional forces and the fasteners can bend, pull out, or tear through one of the surfaces of the cabinet. For shop or utility cabinets the exposed edge of the surface mounted back can be bumped or caught and pulled loose.

Another good reason for a rabbeted back is that the edges of the back aren't exposed. If it's a finished cabinet, it wouldn't be a finished look. The depth of the rabbet for the carcass parts for the back would match the depth of any rabbets or dadoes for the cabinet parts, i.e., tops, bottoms, shelves.

For example: For a base cabinet, machining a dado for the floor to fit into the sides, the floor would be the same width as a back that fits into the rabbet of the same depth. With glue and clamps/fasteners, more strength is achieved than butt joints, and flush mounted backs.
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[jackellis]

Clark doesn't say much about rabbeting the frame for the backs, butafter looking at his web site again, I'm thinking his book would be pretty handy about now.

Thanks for all of the advice and explanations. Dadoes or rabbets it will be in the next set.

[BobSch]

Clark doesn't say much about rabbeting the frame for the backs, butafter looking at his web site again, I'm thinking his book would be pretty handy about now.

Thanks for all of the advice and explanations. Dadoes or rabbets it will be in the next set.

Tom's book is handy if you're looking for cabinet ideas. The best 10 bucks I've spent in a long time.

[jhart]

I would guess that it would somewhat depend on if you are making them for shop cabinets or kitchen cabinets, as to Tom Clark's way of doing it. Tom's would be fine for shop cabinets. If I remember right, he used a roundover bit on the back and says that they are barely noticeable. Tom's way is a method of building good cabinets quickly and still strong and look good for their intended purpose.

[Gator95]

It only takes a minute to rabbet out the back, can't think of a good reason not to do it.