What is an hdo particle board?
My door was/is perfectly flat. I used a 6' level to check it. The Celotex has some minor dips in it, which is where the little bits of unevenness comes from. It hasn't worked into my building though. At least, not yet.
My workbench is 80" x 30". A 4' level would not even begin to make sure it is perfectly flat. I could not even imagine building on a workbench as small as 4'.
I do like the idea of the clamps.
I really wish I had a magnetic workbench.
ORIGINAL: jb86
i use a similar building board, but shim the working surface till it's a flat surface and not warped. don't expect the door under your building board to be perfectly flat. set your building board on it, set a 4' level across your board front edge and rear edge, then diagonal. use thin pcs of balsa to shim (1/32" & up) as necessary to make the board even w/ the 4' level. i build on hdo particle board, i have clamping pads of plywood i screw over the spars (into the particle board) to hold tight to the board, i never liked pinning because the spar can slide around. then i screw down a balsa building board for working on the tail section.
jon b