Haas ST-55S

The Haas ST-55S is a big-bore two-axis lathe built around a 12.5 in (318 mm) spindle bore with an A1-20 nose at both the front and the rear. The spindle is rated 55 hp (41 kW) through a 2-speed gearbox, produces 4,250 ft-lbf (5,762 N·m) at 30 rpm and runs to 1,000 rpm. Z travel and maximum turning length are 44 in (1,118 mm).

Those spindle figures describe a machine for pipe, tube and large rings, not for bar. Peak torque arrives at 30 rpm, which suits heavy cuts and threading on big diameters, where surface speed is already high at low rpm. With a nose at the rear as well as the front, a second chuck can be mounted to hold the tail of a long tube that passes through the bore. The table gives no chuck size and no bar capacity for this model, so the workholding at each end is something to settle with Haas before ordering.

The working envelope is the one the ST-40 has: 35.5 in (902 mm) swing, 30 in (762 mm) maximum turning diameter, 20 in (508 mm) of X and 44 in of Z. The ST-40 spindle has an A2-8 nose, a 4.62 in (117.3 mm) bore, 40 hp (29.8 kW), 1,400 ft-lbf (1,898 N·m) at 150 rpm and 2,400 rpm. Against the ST-40, the ST-55S has roughly three times the torque and a bore about 2.7 times the diameter, at less than half the top speed.

Axis thrust is 5,500 lbf (24,465 N) on X and 9,000 lbf (40,034 N) on Z. The turret has 12 stations with BOT tooling and takes OD and ID tools in any combination; with a BMT75 turret the table gives a 27.5 in (699 mm) turning diameter. The tailstock has an MT6 taper, 42 in (1,067 mm) of travel and thrust from 200 lbf (890 N) to 3,000 lbf (13,345 N).

The 55 hp spindle sets the supply: 105 A at 220 VAC three-phase or 53 A at 440 VAC. Coolant capacity is 95 gal (360 L). Haas's starting price is US$330,995.