Star Micronics ST-20

The Star Micronics ST-20 is a turret-type sliding headstock CNC automatic lathe that takes a fundamentally different approach to 20mm Swiss-type turning. Instead of the gang-type tool post used on Star's SB and SR series, the ST-20 features front and rear turrets with 8 stations each plus a back-working turret with 8 stations, providing massive tooling capacity for complex parts. The ST designation—simple turning—is somewhat misleading, as the machine's triple-turret architecture makes it one of the most versatile 20mm platforms in Star's lineup.

Both spindles run at 10,000 RPM with 3.7 kW continuous power (5.5 kW peak at 60% ED)—notably higher continuous power than the SR-20JII's 2.2 kW. The matched high-power spindle configuration means both front and back machining operations can run aggressively without power limitations. The headstock provides 350mm stroke in standard configuration (317mm with R.M.G.B.), significantly longer than the SR-20JII's 205mm stroke, making the ST-20 better suited for long shafts and extended-length components.

The turret architecture offers unique advantages. Each turret station can hold up to 3 turning tools, and the turret indexing allows rapid tool changes without the physical constraints of gang-type layouts. With front, rear, and back turrets all carrying 8 stations, the ST-20 can accommodate dozens of tools simultaneously—enough for multiple part families or extremely complex single parts. The 12mm and 16mm tool shanks provide flexibility for different cutting requirements.

Running on the FANUC 31i-B5 control with C-axis on both spindles, the ST-20 is a serious production machine. At 4,850 kg and a footprint of 2,988 x 1,720 mm, it is larger than the SR-20JII but delivers significantly more capability. The revolving guide bush unit is standard, with rotary magic guide bush available as an option. The 8.5 kVA power consumption is moderate for a machine of this capability, reflecting efficient servo and spindle drive design.