Ok.... I received my Aluminium for my new cnc via UPS. 470mm X 300mm X25mm

I clamped it down to the original bent Vacuum bed (which temporarily straightened it)... planned the new supported rail bearing block mounting holes in CamBam and successfully drilled and counter-bored the holes. First thing I have ever done with this machine since changing the Z axis plate and adding the 2.2kw Chinese spindle. What an improvement so far !
Still a way to go to make it more sturdy, but I am already planning the next improvements to come.

Now... in respect of holes for clamps on the cutting bed.....For now I am going to drill and tap some holes for clamps. (maybe cutting slots later if needed). What size metric holes should I use for the clamps ? M4/M6 ?? also I am I right in understanding I have to drill a M5 hole to use a M6 x 1mm tap ?