Help with dimensions

[Rick Dohm]

This is probably going to come out overly complicated, but I'm looking for some sort of formula to determine the proper board thickness for a project I'm developing. I will try to describe it since I'm not good enough with Sketchup to illustrate it.

I'm working on a contemporary sideboard type project. The sides will be 8" wide boards mortised into ~2"x2"x18" feet. Between the sides will be a 48"w x 14"h x 18"d cabinet at the top and an open shelf midway between the bottom of the cabinet and the floor. The cabinet will be a frameless carcass with two partitions and 3 doors. The top and bottom (or at least the bottom) of the cabinetwill have extensions to fit in a dado in each side to support it. My question is: how thick should the bottom be to support the weight of the cabinet and its contents without sagging? Contents of the cabinets could be anything from tableware to liquor bottles, so I'm trying to anticipate a fair amount of live loadin addition to the dead load.

All suggestions are appreciated.

Thanks,

Rick Dohm

[Joshua Layne]

The answer (as with most things) is: it depends.
I am not an expert in calculating loads and whether a shelf will bend, nor do you mention what wood you are using (it makes a difference) The sagulator should be able to help though, and will allow you to play with the parameters to see how they influence the outcome.

HTH,
Josh

[Rick Dohm]

Thanks, Joshua. That site helps a lot. I realized after I hit "submit" that I neglected to mention that I am using cherry and that, while a certain amount of "stoutness" will be required, I don't want it to look clunky.

Rick

[Ryan Sparreboom]

At only 18" wide, it doesn't have to be too thick if it's sitting in dados. I'd say 1/2" cherry would be fine, but you could go 5/8" too. If the bottom is also physically connected to the partitions, then you could easily get away with 1/4" or 3/8" thick bottom panel.

Ryan

PS. post some pics of this when your done, it sounds like a nice project!

[Joshua Layne]

After posting the site, I spent some time reading it and I can't say that my gut agrees with some of the information there, particularly the comment on how edging doesn't matter if it is in front of the board or below. Intuitively, I would think that (and this may be the devil hiding in the details) a dadoed and glued support running the length of the shelf (down the middle of the underside for example) would help significantly in stiffening the shelf (same basic principle as an I-beam, but only half... :P)

Why this is relevant to your project is that this type of support would not be visible from most angles, so it won't make the piece look chunky, but will significantly help with rigidity.

HTH,
Josh

[Rick Dohm]

I really don't want to use a support piece on this, but I was wondering if the partitions could be joined to the top and bottom pieces in such a way that it would prevent any sagging. Then maybe thinner stock could be used. Sliding dovetails come to mind, but I've never done one so I'm a little intimidated. Maybe a t-slot router bit? Open to ideas.

Rick