Sizing a vertical Z-axis lift

Z is the axis that gets sized wrong most often, because a vertical move fights gravity on the way up and must hold position when the power is off. Here is how the engine treats it, and where the catalog ends.

Why Z is a lead screw

A belt-driven axis back-drives under load the instant the motor releases. A lead screw with a fine lead (1–6.35 mm/rev) is self-locking enough to hold a modest payload without power and converts motor torque to thrust efficiently. That's why every XYZ system the engine builds puts an LSA lead-screw actuator on Z and belt SBA actuators on X and Y.

The gravity term

For a vertical axis the required torque is the sum of the acceleration torque and the gravity torque — the payload's weight reflected through the screw lead and efficiency — plus any thrust. The engine computes all three and prints them ("Accel | Gravity | Thrust") so you can see that a 3 kg payload at 100 mm/s on a 6.35 mm lead needs about 5.6 oz-in, and that an N17-1 stepper carries it with roughly 178% margin.

Lead selection: speed versus force

A 1 mm lead lifts the most but tops out around 20 mm/s; a 25.4 mm lead reaches 500 mm/s but only moves about 1 kg. The 6.35 mm lead is the usual compromise for lab and pick-and-place Z axes: 150 mm/s with most of the family's payload rating intact. The engine sweeps the motor family at your chosen lead and shows which lead would unlock more speed.

Above 15 kg

The catalog stops at the LSA60's 15 kg. A 25 kg Z — requested more than once through the chat — needs a larger frame (a NEMA 34 screw stage), a brake, or counterbalancing, and is quoted as an engineered axis. The engine will say so explicitly rather than quietly selecting an undersized actuator, and gives you a direct contact.