How much movement to allow for

[Dan Forman]

I'm building a shop cabinet with cedar boards for shelves. They are about 10 1/2" deep, 5/8" thick, and 30" long. They are quite old, light in weight, and have been in my basement for several weeks. Humidity runs around 50% there, and I have a dehumidifier, so not likely to get much worse. How much allowance for movement should I make for them. The rest of the case is birch ply. They will be riding in 1/4" deep dados. I'm thinking of glue and pins in the front, then leave some room in the back of the groove for them to expand but don't know how much. Any other suggestions?

Dan

[Lee DeRaud]

I'm building a shop cabinet with cedar boards for shelves. They are about 10 1/2" deep, 5/8" thick, and 30" long. They are quite old, light in weight, and have been in my basement for several weeks. Humidity runs around 50% there, and I have a dehumidifier, so not likely to get much worse. How much allowance for movement should I make for them. The rest of the case is birch ply. They will be riding in 1/4" deep dados. I'm thinking of glue and pins in the front, then leave some room in the back of the groove for them to expand but don't know how much. Any other suggestions?

DanI think the expansion will be at most 1/8" so you have that issue covered, but 5/8" cedar sounds awfully flimsy for a 30" shelf. Any particular reason for choosing that material?

[Doug Shepard]

This might help
http://www.woodbin.com/calcs/shrinkulator.htm

[Dan Forman]

I think the expansion will be at most 1/8" so you have that issue covered, but 5/8" cedar sounds awfully flimsy for a 30" shelf. Any particular reason for choosing that material?

Lee---I guess the two main factors were that it cost nothing and was just sitting there waiting to be used. This being my first cabinet, it seemed like a good idea at the time. It started out thicker, but after lots of practice with my handplanes and a final trip through the electron recycler to even out the results of said practice, it shrank to current dimensions. I might add that still has a bit of curl in it's width that it wouldn't give up. The cabinet is to organize a bunch of light weight stuff that is currently spreading out, so strength shouldn't be a factor. If need be, I suppose a little oak here and there would shore things up.

Doug---If I operated and interpreted the calculator correctly, movement shoud be minimal. Thanks for the link. Gotta get a moisture meter!

Dan

[Charles Stanford]

You will be most unhappy if you put anything at all heavy on those shelves unless you're going for the antique 'saggy' look.

The expansion across their width should be the least of your concerns.

[Steve Wargo]

Actually if you run them through the sagulator calculator they will delflect less than .04" with a load of 20 pounds distiduted evenly over the length of the shelf. With a load of 20 pounds in the center it will only deflect .06". The human eye will usually not recognize a deflection less than .09" over a 36" span. IMHO I think it's it too thin of stock for the job, but if its what you have it will work. http://www.woodbin.com/calcs/sagulator.htm

[Tim Sproul]

I'd do a stopped dado or stopped sliding dovetail...and fix the shelves to the back. That will make them quite stiff. Be sure to recess the front of the shelf so expansion won't prevent closing of door(s).

[Dan Forman]

Thanks all, the stopped dado in the back with relief in front sounds like the way to proceed.

Dan

[John Hart]

For what it's worth, I built a shelving unit years back with very thin mahogany for the shelves. I ran a thicker rabit piece in the front for support on each shelf and routed a decorative edge on the bottom of those support pieces. The tops of the support pieces were flush with the top surface of the shelves. It worked quite well, and I had some books on the shelves.