Designing Spindle Jacks Step by Step
Designing a spindle jack requires five input parameters: force [N], stroke [mm], travel speed [mm/s], duty cycle [%], and mounting orientation. From these, spindle type, spindle diameter, buckling check, and motor power follow directly.
Correct sizing is essential for reliability and service life. This guide walks you through all five critical design steps – with formulas, examples, and practical notes from TEA application engineers.
Spindle Jack Design Types
Spindle jacks (also called screw jacks or machine screw actuators) convert rotary motion into linear motion using a lead screw. They are available in two fundamental configurations:
Fixed Spindle (Translating Screw)
The spindle (screw) does not rotate – the gear nut rotates in the housing and drives the spindle axially. Advantages: the spindle can be attached to the load, anti-rotation is built in, compact installation length. Used for precise positioning with low to medium loads.
Rotating Spindle (Translating Nut)
The spindle rotates and the nut is fixed to the housing. The rotating spindle extends from the housing. Advantages: higher travel speeds possible, simpler coupling to motor. Disadvantages: spindle must be supported against buckling for long strokes, requires protective bellows.
Trapezoidal vs. Ball Screw
Trapezoidal screws are self-locking (pitch ≤ 4° lead angle), simple, and robust. Efficiency 25–50%. Ball screws have efficiency 85–95%, allow higher speeds and duty cycles, but are not self-locking (require brake) and more expensive.
| Feature | Trapezoidal screw (DIN 103) | Ball screw (DIN 69051) |
|---|---|---|
| Efficiency | 0.30–0.50 | 0.90–0.98 |
| Friction | sliding friction | rolling friction |
| Self-locking | yes (at small lead angle) | no — holding brake required |
| Backlash / accuracy | backlash, limited | preloadable, high precision |
| Wear / maintenance | higher | low, defined lubrication intervals |
| Speed | low to medium | high |
| Cost (relative) | € (low cost) | €€–€€€ (higher) |
5 Design Steps
Step 1: Determine Effective Force
The effective force Feff includes static load, dynamic forces (acceleration), and safety factor (typically S = 1.5–2.0):
Feff = (Fstatic + Fdynamic) × S
Step 2: Determine Required Speed
The required motor speed n results from the travel speed v [mm/s] and the spindle pitch P [mm/revolution]:
n = v / P × 60 [rpm]
Step 3: Check Spindle Diameter
The minimum spindle diameter results from buckling analysis (Euler). For pinned-pinned mounting (both ends pivoted):
dmin = (4 × Fkrit × L²) / (π³ × E) ^ 0.25
With L = unsupported length, E = Young's modulus (steel: 210,000 N/mm²), Fkrit ≥ SB × Feff (buckling safety SB ≥ 3.5)
Note on Euler end conditions:
The formula above assumes pinned-pinned (both ends pivoted) mounting. For fixed-free (cantilever) mounting, the effective buckling length doubles, significantly reducing the critical buckling load. Always verify the actual end conditions in the application.
For applications requiring high positioning accuracy and frequent load-direction reversals, the companion guide Ball Screw Selection covers preload, stiffness, and service life in detail.
Step 4: Calculate Drive Torque
M = F × P / (2π × η) [Nm]
Where η = efficiency (trapezoidal screw: 0.3–0.5; ball screw: 0.90–0.98)
Steps 1–4 can be performed directly in the Spindle Jack Sizing Calculator.
Step 5: Verify Self-Locking
A trapezoidal screw is self-locking when the lead angle φ ≤ friction angle ρ. With a friction coefficient of μ = 0.1, the friction angle ρ ≈ 5.7°. This corresponds to a maximum self-locking pitch of P ≈ π × d × tan(ρ). For ball screws, a brake is always required.
Worked Example: Press Drive
Application: Vertical press for forming operations
- Static pressing force: F = 80 kN
- Travel speed: v = 20 mm/s
- Stroke: h = 200 mm
- Design: Fixed spindle (non-rotating) with trapezoidal screw
- Pitch P = 5 mm/rev
Calculation:
- Feff = 80 kN × 1.5 = 120 kN (with safety factor)
- n = 20 / 5 × 60 = 240 rpm required
- M = 120,000 × 0.005 / (2π × 0.40) = 239 Nm (using Feff)
- Motor power: P = M × n / 9,550 = 239 × 240 / 9,550 = 6.0 kW
Result: A spindle jack with 120 kN capacity, 6 kW motor, and trapezoidal screw P=5 mm is suitable. The low trapezoidal-thread efficiency is what makes the screw self-locking; a ball screw would need about a third of the drive power but is not self-locking.
Lubrication and Maintenance
Spindle jacks require regular lubrication depending on the spindle type:
- Trapezoidal screw jack: Relubricate every 50–100 operating hours with lithium complex grease (DIN 51825 K2K-20)
- Ball screw jack: Relubricate every 100–200 operating hours with lithium or multi-purpose grease (DIN 51825 K3-30)
Practical Tip from TEA:
In our application support we see lubrication failures almost always where the spindle runs outdoors or in dusty environments – the DIN 51825 lithium grease then often lasts only a fraction of the catalogue interval (50–100 h for trapezoidal, 100–200 h for ball screws), because dirt acts as a grinding paste. For dusty or damp duty, state the environment and duty cycle (ED) in your enquiry right away, so we can plan for a protective bellows/wiper and a suitable K3 grease. And do not over-grease: on ball screws what counts is the thin lubricant film in the ball track, not the quantity – too much grease churns, raises the friction torque, and drives up temperature.
Use an online sizing calculator for precise spindle jack dimensioning:
Open Online Calculator →TEA Recommendation
TEA offers spindle jacks in various designs – from single-unit jacks through synchronized multi-unit systems. We also handle complete system design including motor, gearbox, coupling, and control. Standard spindle jacks in various lifting force classes are available in the TEA screw jacks range.
Request Spindle Jack ConsultationFrom design to enquiry: procurement notes
- Cost driver: Ball screws cost significantly more than trapezoidal screws. The price premium pays off at high duty cycles, tight positioning tolerances, or long strokes – for simple lifting tasks a trapezoidal version is usually sufficient.
- Standard vs. custom design: Standard spindle jacks are available for compressive forces up to approx. 100 kN in defined load classes. Custom variants (non-standard pitch, extended spindle, flange interface) become economical at medium quantities – for single units, check whether a standard size fits first.
- Inquiry specification: State lifting force [N], stroke [mm], travel speed [mm/s], duty cycle [%], mounting orientation (vertical/horizontal), and preferred spindle type. TEA can then propose a sizing directly.
- Total cost of ownership: Ball screws have longer relubrication intervals and lower energy consumption due to higher efficiency. At continuous operation or high switching frequency, the more expensive ball screw can be more economical in the long run.
- Further information: Inquiries and sizing consultations via our contact page.
Frequently Asked Questions about Spindle Jack Design
Use the Euler formula: F_crit = π²·E·I / L². For steel, E = 210,000 N/mm² and I = π·d⁴/64. The operating load must not exceed 40–50 % of F_crit. The applicable Euler case depends on the actual end conditions.
Standard trapezoidal screws (DIN 103) for spindle jacks come in pitches of 5, 10, 20, 25, and 50 mm. Fine pitches (5–10 mm) offer self-locking and are good for precise positioning but slower. Coarse pitches (20–50 mm) allow higher speeds but are not self-locking and require a brake or holding device.
P = F × v / (η × 60,000) [kW], where F = static load [N], v = travel speed [mm/min], η = total efficiency (typically 0.3–0.5 for trapezoidal screw, 0.90–0.98 for ball screw). For vertical loads with self-locking screws, also account for starting torque, which can be 1.5–2× the running torque.
Typical duty cycles are 25 %, 40 %, or 60 %. The value is defined by the motor design and heat dissipation. Sufficient rest periods between operating cycles are mandatory.
Use lithium or multi-purpose grease to DIN 51825 K3-30, with a relubrication interval of every 100–200 operating hours. Trapezoidal screws are lubricated with lithium complex grease DIN 51825 K2K-20 every 50–100 hours.
About the Author
Senior Sales & Application Engineer · Technical Sales
Specializes in linear systems and spindle jack design for industrial automation and special machine building.