Designing Spindle Jacks Step by Step
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.
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 free-free 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 free-fixed mounting (one end free, one end clamped), the effective buckling length doubles, significantly reducing the critical buckling load. Always verify the actual mounting conditions in the application.
Step 4: Calculate Drive Torque
M = F × P / (2π × η) [Nm]
Where η = efficiency (trapezoidal screw: 0.3–0.5; ball screw: 0.85–0.95)
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 = 20 mm/rev
Calculation:
- Feff = 80 kN × 1.5 = 120 kN (with safety factor)
- n = 20 / 20 × 60 = 60 rpm required
- M = 80,000 × 0.020 / (2π × 0.40) = 637 Nm
- Motor power: P = M × n / 9,550 = 637 × 60 / 9,550 = 4.0 kW
Result: A spindle jack with 120 kN capacity, 5 kW motor, and trapezoidal screw P=20 mm is suitable.
Lubrication and Maintenance
Spindle jacks require regular lubrication depending on the spindle type:
- Trapezoidal screw jack: Relubricate every 50–100 operating hours with lithium-soap NLGI 2 grease
- Ball screw jack: Relubricate every 100–200 operating hours or every 1,000 km travel
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.
Request Spindle Jack ConsultationFrequently Asked Questions about Spindle Jack Design
In a fixed-spindle jack, the spindle does not rotate – the gear nut rotates instead and drives the non-rotating spindle up or down. This design has the advantage that the spindle can be fixed at the top (attached to load). In a rotating-spindle jack, the spindle rotates and the nut is fixed. The rotating spindle tends to buckle at long strokes and requires a protective tube.
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 0.3–0.6 for trapezoidal screw, 0.7–0.9 for ball screw). For vertical loads with self-locking screws, also account for starting torque, which can be 1.5–2× the running torque.
Spindle buckling (Euler buckling) occurs when a slender spindle under compression load bends laterally. The critical buckling load depends on the spindle diameter, unsupported length, and mounting conditions. As a rule of thumb: the unsupported length should not exceed 40× the spindle diameter for free-free mounting. For longer spindles, use intermediate supports or rotating-spindle design.
Yes, multi-unit synchronization is a common application. Multiple spindle jacks are coupled mechanically via a common drive shaft, ensuring they always travel the same distance. Alternatively, electronic synchronization via servo drives and encoders is possible but more complex. Mechanical synchronization is simpler, more reliable, and preferred for most industrial applications.
Über den Autor
Alexander Olenberger
Sales & Application Engineer · Technical Sales
Specializes in linear systems and spindle jack design for industrial automation and special machine building.