You do not need a center "runner" for a Queen size bed, if you:
1. Tusk-tenon the center slat through the side rails,
2. Use ash or poplar slats,
3. Use spacers to keep the other slats from sliding around.
For an air mattress, 5 or 7 slats are enough. For a futon or foam pad,
7 is minimum, and it works better with a 1/4" plywood base over the
slats, to keep the slats from "telegraphing" through the pad.
One neat trick: Dovetail the ends of the slats, and cut spacer pieces
to go onto the support rails, with angles to match the dovetails. Glue
the spacers in place so the dovetails are a loose fit, so they don't get
locked in if it rains. This is easier than tusk-tenoning the center
slat, if you don't have a mortiser, and it makes a very rigid structure.
Trevor Payne wrote:
> While the runner is Ahistorical, I pretty much is required if one
> makes a slat bead that will accomidate a queen or king sized
> mattress. Without the middle runner the slats bow when you lay on the
> bed. They will soon "pop" off the inner rail and you will end up on
> the ground on your air mattress. :)
> So, either some kind of inner runner or "mid brace" is needed to keep
> the slats from bending and popping out of joint. Otherwise you have
> to beef up the slats so much that they become combersome and impractical.