Structural use of back of cabinet

[Jacob]

I don't think it is a simple observation. I've made lots of furniture out of both solid and manufactured boards. For the solid, I allowed for expansion/ contraction; the ply etc I didn't. I never had a problem with either, ecxept a couple of times when I ignored some basic rules like not sticking a long bit of end grain to a piece of long grain. I have had a look in Joyce. He says, "In all carcass work it should be remembered that while a well-fitted carcass back, grooved, screwed or glued in position will help to achieve overall stiffness and squareness, it will not automatically ensure such rigidity"

Yes I checked with Joyce. He presents every alternative! He says thin or loose backs are a feature of cheap furniture. Oh well, cheap furniture is all I know!
But think I could be right in certain circumstances.
I only thought about it at all because someone I know made an immaculate cupboard with sliding doors, which stuck. He said he thought the solid fixed back would have stabilised it, and it had, but at the back not the front.
I checked several other cupboards and they all had loose (ish) backs, both modern and traditional. Presumably cheap furniture!
Trad chests of drawers need structurally tight front, loose runners, and the back loose without being particularly structural

 

[Jar944]

We solidly attach cabinet backs over here. Typically glued and screwed or nailed into a rebate or groove.

 

[Terry - Somerset]

Just a non-professional perspective.

Without a fixed back, stability relies on the joints to sides, top, bottom. How do traditional joints (eg: M&T or dovetail) compare with those on a plywood carcase (glue, screw, batten?).

I can understand how a fixed back means that most deformation occurring will happen at the front. But with thick man made boards I would expect this to be limited.

Does traditional design contribute to structural integrity - eg: fixed shelves, cross bracing.

In conclusion is it a balance of risk - a loose back allowing transformation into a parallelogram, or distortion at the front causing drawers to stick. Or is it a fuss about nothing - my MDF or chipboard based kitchen cabinets after 14 years of use still haves running drawers and working doors.

 

[Jacob]

Just a non-professional perspective.

Without a fixed back, stability relies on the joints to sides, top, bottom. How do traditional joints (eg: M&T or dovetail) compare with those on a plywood carcase (glue, screw, batten?)
I can understand how a fixed back means that most deformation occurring will happen at the front. But with thick man made boards I would expect this to be limited.

Does traditional design contribute to structural integrity - eg: fixed shelves, cross bracing.

A chest like this would have 3/4 to 1" drawer rails 3 to 4" wide stub tenoned into the sides, and either rails or solid top/bottom dovetailed to solid sides. Bomb proof! Back panel just a detail.

In conclusion is it a balance of risk - a loose back allowing transformation into a parallelogram, or distortion at the front causing drawers to stick. Or is it a fuss about nothing - my MDF or chipboard based kitchen cabinets after 14 years of use still haves running drawers and working doors.

Your MDF cabinets would have planted-on doors or drawer fronts rather then set-in, so hiding any movement. Still need something to keep the thing square - so it'd be the back, or being built in.
PS I'd forgotten how extensive and detailed Joyce is - the book is an essential read!

 

[doctor Bob]

OK he might get away with it but it ...............................................

 

[Drifter2406]

Backs do help the structure especially on cheep furniture, if you have a square box with no back or bracing it will wobble around and the bigger the box the more the wobble. I worked in a fish tank industry before this job and with the amount of weight the cabinets were expected to take without a back they would have collapsed, no fixings other than a groove to sit in all the way round, I work in a kitchen industry now and we staple the backs in, tall units get a brace too.

 

[Fatherclive]

Will add "strength" yes, but to the back, and shifts any movement to the front. Wouldn't matter for open shelves but with doors or drawers could cause them to stick.
Imagine an open ended tea chest on its side - if you stood on top of it the open end (where doors or drawers might go) would bend and distort, the closed end would stay square.View attachment 148903

How did you get a picture of the tv stand I have just made??

 

[Agent_zed]

If it were me I wouldn't worry too much about expansion with plywood. If you are using draw runners you have a couple of mm play anyway. I'd do 18mm box and a much thinner back fixed in place, probably in a rebate to make it neat and strong.

What I haven't seen mentioned though is adding bars across at the front. A couple of horizontal 18mm x 50mm bars will prevent any bowing of the side panels if you put heavy things on top of the cab. If you put them flat so the 18mm is the vertical face then your draws can be made to hide it if you want.

I built a speaker cab out of 18mm ply with finger joints on the corners. Its an open back cab so only has 2 pieces (top and bottom) tight fittting and screwed in place, with about 2/3 of the back open. The front is a floating (couple of screws) baffle of 12mm ply holding the speaker. Its rock solid.