strength and design question...

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I have a design mocked up, but i would like some commentary.1: what size of square tubing should i use? 2x2x3/16 : 3x3x1/4 ? it needs to be able to support 650lbs minimum, there have been days where i have passed out and fallen into bed, i'm no little tike either.2: should i put in an under frame (look at picture)? ;and where at? at the very base or beneath the drawers? 3: http://download.sears.com/docs/spin_prod_831375412.pdf : look at part #8, 11, 12 and 13: where do i get 9in drawers and the ball bearing slides? what parts do i need to mount those? i know amazon and other sites have them, but im having trouble locating the exact parts to fit the drawers. some additional notes: I will be using 2in x 2in x 1/8in angle iron to secure the mattress, and somewhere between 22-16 gauge sheet steel to put on top of the tubing, no drafts from underneath and closes the top off to the drawers to prying eyes and hands. the picture isn't pretty but it works... there will be square tubing in the middle, hence the reason why it looks like its been separated into 4 sections.Last edited by Hobby welder; 01-20-2014 at 02:29 PM.HW, 1965 lincoln idealarc 250 ac/dcEastwood mig135And a bunch of other random stuff.
Reply:2x2x3/16 is plenty, I have a queen size bed made of 2x1x1/8 tube, side rails are 3x1x1/8 tube and cross bars are 1x1x1/8 tube.  That cross in the middle of yours seems like overkill if it's welded in.
Reply:2 x 2 by 3/16 inch seems like a lot to me.   It does depend some on where it is supported.  If you can support it closer to the center vs. the two ends that would reduce the stress.The general formula for stress in a beam uniformly loaded and supported on each end is W x L / (8 x Z).  For 2 x 2 x 3/16 tube, z = 0.75 inches cubed.650 pounds x 75 inches / (8 x 0.75 in.cu. ) = 8125 pounds per square inch.   I usually design for 12,000 psi, which still has a good safety factor.  I would probably switch to 2 x 2 by 1/8 inch tubing, especially since I doubt that you and the mattress really weigh 650 pounds.  ;-)  I was originally thinking that you could go down to 1.5 by 1.5 tubing, but probably not.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Originally Posted by raferguson2 x 2 by 3/16 inch seems like a lot to me.   It does depend some on where it is supported.  If you can support it closer to the center vs. the two ends that would reduce the stress.The general formula for stress in a beam uniformly loaded and supported on each end is W x L / (8 x Z).  For 2 x 2 x 3/16 tube, z = 0.75 inches cubed.650 pounds x 75 inches / (8 x 0.75 in.cu. ) = 8125 pounds per square inch.   I usually design for 12,000 psi, which still has a good safety factor.  I would probably switch to 2 x 2 by 1/8 inch tubing, especially since I doubt that you and the mattress really weigh 650 pounds.  ;-)  I was originally thinking that you could go down to 1.5 by 1.5 tubing, but probably not.Richard
Reply:Drawerslides.com has a huge selection of slides.
Reply:.  I would probably switch to 2 x 2 by 1/8 inch tubing, especially since I doubt that you and the mattress really weigh 650 pounds.  ;-)  Richard[/QUOTE]i did some math and looked at it the other way..like the 650 pounds is just right if you figure 50 for the mattress and 600 for him and his frens...