Why is a heavy iron base vital for a good machine?

[guido]

Cast iron in itself has better dampening properties then steel.
However in a machine construction the dampening properties of the connections between different parts/sections of the machine is much more relevant.

Steel has a higher E modules then cast iron wich means u can build a lighter machine with same stiffness.

Guido

[Mcgyver]

ooops replied to wrong post...

ci as I am able to look it up has twice the vibration dampening properties of steel.

[ImanCarrot]

Granite... mehe I got an MSG 325 Air Bearing Spindle machine that I turn optics with. It sits on a 5 tonne granite base on air pads, everything is vibration isolated and the spindle is temperature controlled by liquid cooling. It's positioned by laser interferometers and stuck in a temperature controlled lab.

I make optics down to sub micron tolerances on form (peak to valley)- you can't go much lower than this without hand lapping which I can do to 1/20th of a wavelength of light at 633nm wavelength after 1/20th of a wavelength you hit diffraction limitations (ie light starts diffracting).

I'm cutting small 17mm dia aspheric/ hybrid optics in plastic at the moment with a form error less than 1 micron p-v across the whole batch of 75

It can be done. You just need to control all environmental and vibration issues, your tools have to be precisely formed and you got to have lots of patience haha!

Oh, forgot to say, I use Single Point Diamond Tools, even slamming the lab door when it's machining will give a bad surface. Gotta love it!