I have now got hold of a piece of scrap 18mm block board, so here is the correct base board set up.
18mm thick board (MDF, block board, chip board etc) cut to the size you prefer.
25mm x 48mm batten (2" x 1")
2 counter sunk headed M6 bolts (or 1/4" for our colonial brethren)
2 M6 T nuts for wood, or 1/4 " to suit
Cut the base board the size you require, then cut the batten to the same length.
Drill the four pillar mounting holes as per the earlier Instructable on making a mount.
Here I have recessed the mounting holes with a hinge cutter (the ones for kitchen cupboard doors), the cutters are cheap and readily available. I used a 25mm (1 inch) cutter.
The hex bolts have penny washers on them to spread the load.
Mark the centreline and clamp the batten to the bottom. Drill and countersink 2, 6mm holes from the top of the board straight through both pieces of wood.
Keeping the clamps in place turn the boards over and drill a 7mm relief about 6mm deep for the captive T nuts.
Hammer the T nuts in.
Step 1: Fix the Batten
Turn the assembly over and push the two countersunk 6mm machine screws through both boards and screw them down into the captive T nuts.
Re-assemble the mount. Here I am using the flexible shaft drive of my El-Cheapo rotary tool. The spacers for this turned out to be standard washers.
Make sure that the countersunk screws are flush with the surface.
Step 2: Using the Tool
The batten can be unscrewed for portable use, or as here, clamped into a 'Workmate'
I have this set up as a simple drum sander, but you can add clamps and fences for other work.