[Scrit]

Well I've now built a test piece of matrix bed. It comprises a 32mm (1-1/4in) thick harwdood plywood underside support for ridgidity with a 25mm (1in) high density polyethylene top screwed on. I surfaced everything both sides with a trepanning cutter before and after assembly then machined 6.35mm (1/4in) round-bottom grooves in a chequer-board pattern on the top surface some 7.2mm deep. The whole thing has a gutter round the outside and the islands are 28 x 42 mm (same size as the Biesse auxilliary pods off newer machines). These islands have a 0.5mm deep x 12mm groove milled across them from side to side. This is a small bed some 605 x 310mm in size (approx.) with a 6 x 17 island grid and has a ten vacuum draw holes of 4mm diameter drilled in the middle of selected islands and with the exhaust connections made by filing a notch in the thread of G1/4in threaded pneumatic hose connectors which are then screwed into the underside of the bed. From there hard polythene tubing connects everything back to a couple of brass manifolds 6-into-1) and thence to the vacuum pump. The vacuum draw holes are deactivated by screwing a self-tapping screw into them. The vacuum area is "defined" by inserting 8mm foam rubber cord into the grooves around the outside of the area to be put under vacuum. The bed certainmly seems to work well with timber and composite timber materials although a smaller matric, say 25 x 25mm, might be more effective.

Can anyone suggest a material to sit between the matrix table and the workpiece which will allow me to machine through but still retain vacuum or is it a case of machining tabs onto the workpiece and trimming off after removal from the machine? I'd particularly like to machine 2 to 3mm thick ABS for a product.

Regards

Scrit