French cleat question

[Ian Dodd]

Here's one for the structural engineers on the Wreck:

In the fall I'll be taking an intermediate/advanced woodworking class at the community college. I've been sketching ideas for a chest of drawers for our master bedroom. Actually, it's two mirror imaged, interlocking pieces (think of the Chinese yin-yang symbol), but for our purposes here think of a casework 84" long by 24" deep by 32" high.

I had been having trouble coming up with a base/foot/leg design that worked with the rest of the piece. Then it occurred to me: why not "float" it on the wall, hanging it off a pair of French cleats, leaving a comfortable 3-4" toekick space underneath?

Here's my structural question: How much does a 7 foot long chest made of hardwood and full of clothes weigh? And if I have a pair of 3/4" hardwood cleats screwed to the studs in the wall will that hold it? What size screws? How much stress is being put on the casework itself since it's not being supported from beneath? And, most importantly, what sort of design considerations do I need to take when I build it to withstand those stresses?

Any thoughts will be appreciated.

Ian

[Hoyt Weathers]

It could be done if you have a 6" thick steel-reinforced concrete wall to hang it on. I assume you do not have that. Therefore I would never attempt it with a normal tubba4 stud wall. Why don't you just go with feet hidden from the front and sides? Would that harelip the county?

Hoyt W.

[Fred]

Speaking strictly from ignorance... this sounds a lot like the standard structure of upper kitchen cabinets. Perhaps not the French cleat, but the loading would probably be lower for clothes than for china. A couple of 3in screws in each stud sounds OK to me. Fred

[charlie b]

Since you've probably got this thing drawn up to scale and have a parts list you can calculate the cubic inches of each part L(inches) x W (inches) x Thickness (inches) = Cu In /1728 = Cu Ft so 84" x 24" x 3/4" = 0.88 cubic feet x 2 pieces (top & bottom) ----- 1.76 Cubic Ft

34" x 24" x 3/4" = 0.33 cubit feet x 4 (left,right & two in betweens) ------ 1.32 Cubic Ft 84" x 32" x 3/4" = 1.17 cubic ft x 2 pieces (front & back) ----- 1.34 Cubic Ft

Total Cubic Ft = 5.42 call it 5 1/2 X 35-45 pounds/cu ft ------ 190-244 pounds Throw in another 20% or so for drawer sides, guides etc and you're looking at *** 230-290 pounds without clothes ****

If the wall studs are on 16 inch centers AND you hit them just right, the cleat on the wall will be in 5 studs, each carrying about 50-60 pounds.

On the case side more info is needed. This thing going to have a 3/4 ply back? If so, how's it going to be attached to the piece and accomodate wood movement? If this is a two parter that's 115 - 145 pounds per unit If each is hung on it's own cleat per your the Yin/Yan description neither will hit all 5 studs - and each may only hit 3 studs but there could be overlap so the weight could be over the equivalent of 6 studs, or 40-50 pounds per stud.

=================== what sort of design considerations do I need to take when I build it

Since people lift things by their top, and lean things back to get under them - most traditional joinery - dadoes, dovetails, finger joints, mortise & tenon, splines etc. handle that sort of abuse adequately. I'd skip rabbeting//rebating because of the open end thing.

Should be enough info to get you thinking through your problem and coming up with answers.

Good luck and have fun! charlie b

ps - if you dovetail the top and bottom to the sides PUT THE PINS ON THE TOP AND BOTTOM AND THE TAILS ON THE SIDES (or you could have things fall apart - DAMHIKT)

[Ian Dodd]

Wow, Charlie, thanks for all the help. I'm sorry I didn't respond earlier but I access the newsgroups through Google and they hadn't updated in several days. A few caustic e-mails and they seem to have fixed the problem. Anyway, your contribution was great.

As for joining the sides and top, I wasn't planning to go dovetails, but rather oversized box joints that are also pinned (think Green & Greene brothers for inspiration). When I looked up your final acronym I FOOMCROTFLMAO. But let me ask this, do you see a problem with my planned joints?

[philski]

Out West, (Idahoish) they don't call 'em French Cleats anymore... now they are called Freedom Cleats!

Philski