Drawer bottom thickness?

[MBG]

I'm building some drawers for an under the TS cabinet. In the past I have used 3/16" luan ply on many drawers. My shop cabinet will have four sort of large drawers (approx. 25-1/2"w x 24"d). The top two are small in height and will be lightly loaded but at least the bottom one will be storage space for my sanders. What is the rule of thumb on drawer bottom thickness?

(Also, how much clearance should I provide in the groove to slide the bottoms into?)

Thanks,

Mike

[Warren]

If you are speaking of the depth of the groove. I like to go about half the thickness of the drawer sides. I'm not one for measuring, I use set up bars and a usually critical eye.

Can't speak with a lot of authority regarding the thickness of the drawer bottom. Are you inserting the bottom into all four sides? Some omit the back. I would be satisfied with quarter inch to three eights for the shallow drawers. Maybe a little thicker for the big drawer depending on the size of your sanders (humungous belt sander?) and what else you are going to throw in there over the years. (Note: I would be satisfied until there was a failure and then I go to a thicker size.)

[LarryG]

For the two upper, shallow drawers, the usual 1/4" thick drawer bottom ought to be sufficient. Center desk drawers are often about that same size and do okay with 1/4" bottoms. But I agree with Warren that 3/8" wouldn't necessarily be overkill, since this is a shop cabinet.

For the deeper bottom drawer that will hold power tools, I'd use at least 1/2" and possibly even 3/4". The work will be the same the the difference in cost minimal.

Drawer bottom thickness is partly a function of how the drawer slides. The bottom acts as a diaphragm that keeps the four sides of the drawer body from racking. If you use good-quality, full-extension slides, the forces applied to the drawer as you open it will be pretty small since the drawer will glide open and closed fairly effortlessly, even when loaded. If the drawer just slides within the cabinet directly, or on wooden runners, opening and closing it will subject the body to higher forces because of the increased friction (which increase the more heavily the drawer is loaded), and as the body tries to rack the bottom will try to distort. A thicker bottom will resist the distorting forces better than a thinner one.

[JimD]

Another factor is how the bottom is attached to the sides. It sounds like you will locate the bottom in a dado at least a little way up the side. This is good, expecially when the bottom is thin enough it may flex a little. For a drawer with heavier contents, using the same thickness material but going a bit further up the side can help to keep sag in the bottom from becoming an issue. I have shop drawers with 1/2-3/8 thick bottoms but with the bottoms fastened directly to the bottom of the drawer. I have more sag issues with this arrangement than with other drawers with 1/4 luan in the normal dado 1/4 to 1/2 inch up the side. The other thing you can do is to use the thin bottom but add a center support (possibly after seeing if you really need it).

Jim