A lift raises a 180 kg carriage with a 320 kg payload by 1 m, holds it at the top while it is unloaded and lowers the empty carriage. A motor at the bottom drives a Ø40 × 10 mm ball screw with a single nut and no preload. This tutorial rebuilds the Ball screw lift (single nut, no preload) example, reads its results and tries three changes.

The numbers are those of this version of Axomek. To compare: open the Ball screw lift example. It starts a new project from the example in place of yours, so save yours first (the app asks) and come back to it with Switch project (Ctrl+P).

Step 1: add the screw

Start a Blank project and open Ball screws in the navigation.
Choose + Ball screw. Screw BS1 appears.
Set Name to Lift screw and enter the values of the catalogue screw:

Group	Input	Value
Ball screw shaft and nut	Nominal diameter d₀, Root diameter d₂	40 mm, 34.1 mm
	Lead Pₕ	10 mm
	Dynamic rating Cₐ, Static rating C₀ₐ	38 000 N, 80 000 N
	Nut preload	0 N
	Friction μ	0.005
Mounting	Unsupported length	1100 mm
	End fixity	Fixed – supported
	Compresses the shaft	Positive forces
Balls (internal geometry)	Ball diameter Dw	6.35 mm
	Loaded turns per circuit, Circuits	2.5, 2
	Nut outer diameter	67 mm
Requirements	Min life, Min static safety	20 000 h, 2

A Nut preload of 0 is a single nut with backlash. The fixed bearing sits at the bottom next to the motor and the top end runs in a floating bearing, hence Fixed – supported.

Step 2: turn the masses into a load spectrum

The weight acts on the nut in every step, so every force is positive (down). Fill Axial force, speed and time share with three rows:

Step	Force	Speed	Share
Lifting: (180 + 320) kg × (9.81 + 0.5) m/s²	5155 N	900 rpm	25 %
Holding at the top: 500 kg × 9.81 m/s²	4905 N	0 rpm	60 %
Lowering empty: 180 kg × 9.81 m/s²	1766 N	1500 rpm	15 %

Lifting adds the 0.5 m/s² of the acceleration to gravity. 900 rpm × 10 mm is 9 m/min.
Lowering the empty carriage runs at 15 m/min, so it takes 15 % of the time where lifting the same metre took 25 %.
Holding counts with 0 rpm: it is part of the operating time but turns nothing. The life counts revolutions; the static safety takes the holding force too.

Because the weight always points down, the screw is compressed between the nut and the fixed bearing below it in every step. That is why Compresses the shaft is Positive forces.

Step 3: read the results

Result	Value
Equivalent loads 1 / 2	4146 N / 0 N
Equivalent speed	450 rpm
Rating life	28 524 h, 770.2 million revolutions, 7702 km travel
Static safety	15.52 at 5155 N
Critical speed, allowed 80 %	5314 rpm, 4251 rpm
Buckling load, allowed 50 %	228 150 N, 114 075 N
d·n	60 000
Efficiency, lead angle	0.9405, 4.55°
Drive torque at 5155 N	8.723 N·m
ISO 3408-5 ratings from the geometry	Ca 43 982 N, C₀a 117 031 N (19 balls a turn, 5 loaded turns)
Axial rigidity (ISO 3408-4)	135.9 N/µm
Largest ball load at 5155 N	80.9 N, 1.07 × the mean of 96 balls
Contact pressure, screw / nut	1494 MPa / 1356 MPa
Life from the balls (scaled to Ca)	26 558 h

Check	Value / limit
Life	28 524 h / 20 000 h
Static safety	15.52 / 2
Speed	1500 rpm / 4251 rpm
Compressive shaft force	5155 N / 114 075 N
d·n	60 000 / 70 000
Ball static safety	22.22 / 2
Contact ellipse margin to the groove edge	11.49° / 0°

How to read it:

Equivalent load 2 is 0: no step loads the other flank. Its life is infinite and the life of flank 1 is the screw's life. The backlash is never crossed.
The equivalent speed 450 rpm is 0.25 × 900 + 0.15 × 1500. The 60 % of holding lowers it, so the life in hours includes the time the lift stands still.
The life from the balls agrees with the ISO life within 7 %. Both rate the same single nut.
The motor needs 8.723 N·m while lifting, about 0.82 kW at 900 rpm, plus its own acceleration torque.

Step 4: add a preload

Set Nut preload to 2000 N (about 5 % of Cₐ). The nut is now rated as a double nut, each half with one circuit:

Result	No preload	Preload 2000 N
Equivalent loads 1 / 2	4146 N / 0 N	4202 N / 384 N (nuts)
Rating life	28 524 h	27 386 h
Nut halves at 5155 N	one nut	5233 N / 78 N
Largest ball load	80.9 N	156.1 N
Ball static safety	22.22	11.53
Life from the balls	26 558 h	22 031 h
Nut stiffness at 5155 N	1058 N/µm	829 N/µm
Preload torque	0 N·m	0.56 N·m

All checks still pass, but the lift gains nothing: the lifting force nearly lifts one half off, so 48 balls carry what 96 carried before, and the nut is less stiff at the working load. The preload only takes up play the weight already takes up. Set Nut preload back to 0.

Step 5: hang the screw from the top

Move the motor and the fixed bearing to the top: the weight now pulls the screw between the nut and the bearing. Set Compresses the shaft to Negative forces.

The largest compressive force becomes 0 N and the buckling check passes at 0 %. A hanging screw cannot buckle under its load. The critical speed does not change, because it depends on the length and the end fixity, not on the load.

Set Compresses the shaft back to Positive forces.

Step 6: drop the top bearing

Set End fixity to Fixed – free, as if the screw stood on its motor without a top bearing.

Result	Fixed – supported	Fixed – free
Critical speed, allowed	5314 rpm, 4251 rpm	1212 rpm, 969.4 rpm
Buckling load, allowed	228 150 N, 114 075 N	27 881 N, 13 941 N

Speed fails: lowering at 1500 rpm is 155 % of the allowed 969.4 rpm. The free end lowers the critical speed by more than four times. A free end only suits short screws or low speeds. Set End fixity back to Fixed – supported.

What you learned

On a vertical axis the weight loads one flank in every step. A single nut without preload carries it on all its balls, and its backlash never shows.
A standstill step counts in time but not in revolutions.
A preload helps where the force changes direction. Under a one-sided load it halves the balls that carry, adds friction torque and can lower the stiffness at the working load.
Put the fixed bearing where the load pulls the screw if you can. A free end costs most of the critical speed.
A ball screw is not self-locking: a vertical axis needs a brake.