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I cut out the centre to allow it to fit around the cast steel table this will help in positioning it.
I drilled three 8mm holes 40mm from the edge and used epoxy to secure in 3 8mm coach bolts, with heads flush to the surface. I used a Forstner bit to create the hole for the head first then drilled the 8mm hole for the shaft of the bolt. The two pieces of Melamine were then glued together ( I used liquid nails for this), clamped for a few days to dry.
I had some 3mm x 25mm flat steel which I cut 3 x 75mm long, drilled a 10mm hole in each 13mm in from one end, then 15 mm in from the other end I rough bent to 90deg to form an L. These will be the holding clamps for the table top. So I don't ruin the centre when drilling through and so it can be used as a Bobbin Sander, I cut out a 100mm dia section using a hole saw. This is a sacrificial piece and I can make as many replacements as I need.
Fitted at last and it can now be used the knobs are from the hold down clamps I got from McJings (I have to go get three more to replace them) . The fence is made and only needs the the brackets fitted.