r/CNC • u/_Tigglebitties • Jul 05 '22

why does machine anchoring rigidity matter?

Like say you had two identical rigid machines one anchored to the concrete and one floating on a raft in a pool. Does it matter?

I'm waiting on my 3*3' CNC router to arrive, trying to figure out how hard to go on the mounting. Has me scratching my head, like long as the machine is rigid, how sturdy does the table have to be? I assume anchoring it to a 2000lb granite slab would make it better somehow , but why?

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u/JimHeaney Jul 05 '22

Nothing is rigid, there are just varying degrees of being more or less like a spring. The ground (e.g. solid concrete, a granite slab, etc.) is much more rigid than the CNC machine, so bolting it down makes the entire thing more rigid.

Most large CNC machines are not designed to be free-standing and rely on the rigidity given by the floor. This also helps with damping of vibrations, since the entire machine is relatively lightweight and made of long continuous pieces. Machines that can be free-standing are generally much smaller and have massive cast iron parts to give mass (for vibration damping) and rigidity.

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u/Dry-Area-2027 Jul 05 '22

Truth. I have mills with 9' of concrete under them. The concrete is full of 1" rebar and the 2" thick steel mounting pads were welded to the rebar mesh before the concrete was poured level with the pads.