we've got plans to have a nice trundle bed in the corner of the guest room. The sketch-up (ketchup) drawing below shows the plywood components, excepting the one cross beam (more on that further down). These will then be clad in reclaimed redwood frame and panel facades.
For us, we wanted as low a profile as possible with the bed as it's going to mostly be used as a spot to lounge on and it's nice to be lower slung. But trundle beds tend to have a really tall profile due to the need for an extra tall span running along the opening for the lower mattress and all it's required debris. We're opting for futons with ~ 6" of loft. Casters are around 1,1/4" tall.
I talked to dad about it. he did a few quick sketches and sent them my way, recommending an aluminum I-Beam construction for the span. His calcs indicating that 2, 2" wide by 1/8" thick soft aluminum straps in a 4" I-beam should support 300 pounds of human pretty well along a 6' span. So it goes.
I concluded today with the beam, a lamination of doug fir that's 4,1/4"x2,1/2"x79,1/2" with the alu straps recessed into place. Epoxy and 2" flathead screws secure it to the wood. This ought to work, hopefully!
