Originally Posted by
hanermo
A so-called double column mill, with moving table, is the most rigid solution.
Cannot be done for milling steel in 350 kg.
I built one.
And my table alone is 200 kg in mass, for 1600x600 mm in table size.
Total mass is 2000 kg, approx.
All in steel, all bolted, linear guides, ISO30 spindle, automatic toolchange via pnematic drawbar.
Y axis == 400 kg.
Columns 270 kg each, 250 x 400 x 1400 mm with 12 cm risers (35 kg each), x 2, 540 kg approx.
The vertical head is about 500 kg, and is supported by 2 gas springs, of 2500N or 250 kgf push force, each.
Rigidity about 0.03 mm deflection under 87 kgf load, so == 30 microns / 870 N, or == 29 N / um.
But I have 500 mm max vertical movement, travel, with 1000 mm tall linear rails, and 500 mm tall edge-edge contact surfaces on the rails.
Rails are 35 mm HIWIN, 6 of, on z, with 12 blocks.
Theoretical load 4000 kg per block, x 12, or about 48 metric tons rated load capacity on z.
You have to have that, to get the z axis deflection under control.
I tried 5 times, in 10 years, to get it right.
The rigidity improved from about 0.28 mm to 0.03, or about ten times, over 5 iterations.