Marking for drilling - or more sawing....

Well, I said I wanted to post about errors as well as successes, so here's the first. Having made my MDF base 24 " wide, I realise now that sitting the metalwork on the MDF won't give the x-stage stepper motor any room at all, so I am cutting 3.6 cm off down the left side of the MDF base when looking at its bottom face, which is where I am marking the drill-holes. I may need to move the whole assembly backwards, but time will tell, or I may need to use feet to lift it off the floor, but as I don't know what motors I'll be using yet....

Anyway, I have drawn diagrams of where to site the drill holes:



I shall use the countersink 5 mm screws I bought earlier today. I have measured the top of the screw at 9 mm, so I have also marked a 9 mm line across the marked positions on the MDF so that I can drill a countersinking hole to the right size - drilling from underneath. I shall also drill 3 mm pilot holes right through the MDF and 5.5 mm holes through the metalwork.