What size clamping holes ?

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 ?

I wouldn't use anything less than M6, but you don't want them to be too big as the fasteners and clamps may get in the way, so either M6 or M8. You are correct in saying to tap M6 you need to drill a 5mm hole.

Great thanks Jonathon.

I have drilled the holes 10mm deep. hope this is enough.

I know when I used to build motorcycles 20 years ago, it was unadvisable to put stainless bolts into Alu unless you coated the threads in copperslip first, as over time the stainless would weld itself to the Alu. So I guess you all use mild steel bolts to mount the rail bearings to the table ?

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Originally Posted by dudz

Great thanks Jonathon.

I have drilled the holes 10mm deep. hope this is enough.

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You'd be better drilling the thru holes then they don't fill with swarf or chips. If you can't do that then think about removable plugs or set screws.

good point jazz Thx. I might use set screws

Attachment 7795Here is the finished Cutting bed. My first job on this machine. When i mount the new rails, I will skim the surface of this bed for trueness.

I still need to work on my drilling methods. When I used the counterbore endmills it seemed to cut with ease. When I drilled the holes with 5mm and 6mm HSS bits, it screamed like a "B$*ch" . Im not sure if I had the feedrates etc correct. Sounded like the Bits were blunt to me. / plunge rate 0 / Cutfeedrate 800 / Peck 2mm / spindle speed (I tried 8000 - 15000 ) / Target depth -11mm / tool dia 4mm and 6mm / used cutting fluid and air.
Where do I put the input "400mm/min" for spiral down ?? can't find this in cambam for drilling (only for pockets and profiles), only cut feedrate in drilling .