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Material Thickness for Pickup Bed Toolbox

I have a plywood box in the back of my pickup that holds long stuff (tripods, prism poles, digging bars, shovels, long stakes, etc.). It has stood up well to the loads I've placed on it, but after almost 15 years of exposure to the weather it's falling apart.

I'd like to replace it with an all-aluminum box for reasons of durability and appearance, and maybe even some weight savings. However, I don't know how thick an aluminum top I'll need to obtain the same kind of performance I've gotten with 1/2" plywood.

The current plywood top spans openings ranging from 10" to 18", and it hasn't balked at being jumped on or having sacks of concrete and sand stacked on it. I'll need the aluminum top to do the same thing. Since I'm interested in saving weight and cost, I'd like to find the sweet spot between weight/cost and a top that's too thin to bear the load.

Is there a formula that would allow me to size the aluminum top for this application, or is this a seat-of-the-pants/try-it-and-see/if-at-first-you-don't-succeed proposition?

TIA.

Reply to
Jim Frame
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On Thu, 11 Oct 2007 21:43:39 -0700, with neither quill nor qualm, Jim Frame quickly quoth:

Aluminum diamond plate comes in 0.125" thickness and is fairly common. Check the specs on 3003 and 6061 alloys, MSC's choices of diamond plate.

0.080" is also common, but how many bags of cement do you want on top and how sturdy is your frame? More fasteners (and/or a single sheet top) means more weight-carrying ability for thinner stock.

After looking at MSC's prices ($30 s/f), I'd look for a local scrap yard to source it if I were you. Ye gods! 4'x4'x0.125" is $168 at MetalsDepot.com, or 4'x4'x0.060" plain steel sheet is just $45 (or roughly $3 s/f., with $227 FedEx Freight shipping on top) Yeah, you'll just have to find it locally, won't you?

Vendor metalstogo on eBay is much cheaper for al di plate, though.

16 Ga. steel sheet is 2.5 lbs per s/f, 14 ga. is 3.12 lbs per s/f. 1/8" aluminum plate is less than half that weight with equivalent (SWAG) strength.
Reply to
Larry Jaques

I'm thinking about 1/8" smooth aluminum for the top (I have some equipment that I don't want to subject to bump-bump-bump as I slide it across the top during loading and unloading) and sides, with 0.10" AL for the interior dividers. However, in my current design I have an open span of about 24" x 24", supported on only 3 sides (i.e., one side is open to the tailgate). Any sense of whether this is too much? Would I be likely to bend the open side downward by stepping on it?

In formulating these questions I've come to the conclusion that I need to pick up a piece of 1/8" AL sheet and give it some real-world testing. Thanks for getting me moving in the right direction, and I welcome any further comments from anyone with pertinent insight.

Reply to
Jim Frame

On Fri, 12 Oct 2007 14:47:36 -0700, with neither quill nor qualm, Jim Frame quickly quoth:

Sliding sacks of concrete over diamond plate would open them, too. Smooth is good. Cheaper, too. Check Ebay for those definitely better prices on 2x4' AL.

Absolutely. No question. (Unless you weigh 35 pounds.) I'd at least run a 5/8" square steel tube across the top, under the AL. (No, I didn't do any calculations there, so it's a plain ol' WAG.)

Reply to
Larry Jaques

Jim, what you describe in your first paragraph reminds me of my 40+ years of land surveying.

Ivan Vegvary

Reply to
Ivan Vegvary

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