Zero Backlash vs. Backlash: What Does Your Application Need?

Zero backlash means drive components with no measurable reversal play — typically <1 arcmin. Backlash-affected systems have 5–50 arcmin of torsional play. This choice directly determines positioning accuracy, cost, and maintenance effort.

Zero-backlash components often cost 2–5 times as much as standard components. But for some applications this investment is indispensable; for others it is completely unnecessary. This guide shows when zero backlash is critical and when backlash is sufficient.

What Is Backlash?

Torsional backlash (also called reversal backlash or backlash) is the angular deviation between the drive axis and the output axis when the direction of rotation changes. It is measured by applying torque to the drive side and measuring the angle by which the output side shifts before it responds.

Measurement and units:

• Unit: arcminutes (arcmin) or degrees (°). 1° = 60 arcmin.
• Practical threshold values:
• <0.5 arcmin = High precision (robotics, medical technology)
• <1 arcmin = Zero backlash (positioning drives)
• 1–3 arcmin = Reduced backlash
• 3–10 arcmin = Moderate
• >10 arcmin = With backlash (conveyor technology)

Torsional backlash is caused by several factors: tooth flank clearance in gearboxes, bearing play, elastic deformations under load, manufacturing tolerances.

Zero-Backlash Components

Planetary Gearbox with Zero Backlash

High-quality planetary gearboxes can be designed with torsional backlash <0.5 arcmin. This is achieved through: (1) Increased manufacturing accuracy (quality grade 5–6 per DIN 3961–3967), (2) Preloaded bearing packs, (3) Elastic or spring-loaded planet carriers, (4) Profile correction to optimize tooth flank contacts. Such gearboxes are standard in robotics and medical technology. They cost approximately 3–4 times more than standard planetary gearboxes.

Bellows Coupling

Bellows couplings guarantee torsional backlash <1 arcmin and are the standard interface for zero-backlash positioning drives. The folded bellows (usually elastomer or metal) transmits torque without mechanical play. Bellows couplings cost 200–500 € for small sizes, but offer an extremely reliable zero-backlash connection.

Preloaded Guides and Bearings

Angular contact bearings or needle bearing packs can be mounted under preload to eliminate radial and axial play. This is often more economical than a new gearbox generation. Typically, two bearings with opposing contact angles are arranged and preloaded by locking nuts. This reduces bearing service life by approx. 20–30 %, but provides zero-backlash function. Zero-backlash roller guides such as TEA LinRol/LinTrek systems achieve <1 arcmin thanks to preloaded guide rails. The choice between a press fit (e.g., H7/p6 for permanent mounting) and a transition fit (e.g., H7/k6 for serviceable connections) is governed by ISO 286 — see our reference for ISO fits H7/H6 with µm-values for the most common shaft diameters.

Components with Backlash

Worm Gear

Worm gears have high susceptibility to wear and backlash development due to their design. Typical values: 5–20 arcmin when new, 20–50 arcmin after a few years of operation. This is due to the sliding contact type (worm on gear) and high friction. However, worm gears are very compact, enable high gear ratios, and are cost-effective. Not suitable for positioning drives, but acceptable for conveyor technology.

Jaw Coupling

Jaw couplings with elastomeric inserts have torsional backlash of typically 3–8 arcmin, depending on the elastomer material and wear. This is acceptable for general mechanical engineering drives but not for positioning. They are robust against contamination and shaft deflection.

Standard Rack and Pinion

Racks per DIN 8 with standard module have flank clearance of 1.0–2.0 mm (depending on module). This leads to torsional backlash of 10–30 arcmin for typical pinion sizes. They are cost-effective and ideal for conveyor technology, but unsuitable for precise positioning. Where reduced flank clearance is required, reduced-backlash racks made to drawing are the answer.

When Is Zero Backlash Critical?

1. Positioning Drives

Axes that must repeatedly travel to exact positions (machine tools, robots, handling systems) require zero backlash. Even a small backlash of 5 arcmin translates to a linear positioning error of approximately 1.45 mm at a 1-meter lever arm (tan(5/60°) × 1000 mm). In multi-axis systems, these errors compound. Typical requirement: <1 arcmin over the entire machine lifetime.

2. Highly Dynamic Applications with Rapid Direction Changes

Robot wrist axes that perform many motion reversals per second require zero backlash to minimize control deviations. Torsional backlash directly affects trajectory errors.

3. Reversal-Backlash-Sensitive Applications

Applications where torque frequently changes direction (e.g., oscillators, valve drives with rapid closing) are particularly sensitive to reversal backlash. Control becomes unstable when play is large. Requirement: <3 arcmin for stable control.

4. High-Precision Measurement Technology and Medical Applications

Surgical robots, precision measuring instruments, and laboratory automation require <0.5 arcmin, since errors here can endanger human lives. Here, zero backlash is not optional but a safety requirement.

When Is Backlash Acceptable?

1. Conveyor Technology and Drives without Positioning Requirements

Conveyor belts, elevators, pump drives – anything where only uniform speed and torque matter, not exact positions. Here jaw couplings or worm gears are perfectly adequate with 5–20 arcmin.

2. Force-Controlled Applications

Applications that maintain a constant torque (not an exact position) – e.g., presses, roller drives, torque limiters. The play is "taken up" by the force and plays no role. Requirement: <10 arcmin is perfectly sufficient.

3. Non-Critical Drives with Long Cycle Times

Drives that rarely start/stop or run continuously at speed – e.g., fans, compressors, standard electric motors. Play only matters at start-up. Requirement: <15 arcmin is sufficient.

Comparison Table: Backlash of Components