Beta – TEA Academy is new. The content is for learning; it has been prepared with care but has not yet been technically approved. It does not replace design based on the manufacturer’s specifications. Found an error? Write to us.

← Back to Module Overview
MODULE 7 · UNIT 2 OF 5

Backlash-Free or With Backlash?

approx. 7 min · Learning goals, example, knowledge check

Learning goals — after this unit, you will be able to …

  • Define torsional backlash and convert it to a linear positioning error;
  • Assign components with and without backlash to typical applications;
  • determine when zero backlash is required and when some backlash is sufficient.

What is torsional backlash?

Torsional backlash (also known as reverse play) is the angular deviation between the drive shaft and the driven shaft when the direction of rotation changes—caused by tooth flank clearance, bearing play, elastic deformation, and manufacturing tolerances. It is measured in arcminutes (arcmin); 1° = 60 arcmin. Rough classification: < 0.5 arcmin high precision, < 1 arcmin backlash-free, 1–3 arcmin reduced backlash, 3–10 arcmin moderate, > 10 arcmin with backlash.

From torsional backlash to positioning error

Torsional backlash only becomes tangible when it is converted into a linear positioning error at the effective radius:

s ≈ R · φ (φ in radians)

s = positioning error · R = effective radius/lever arm · 1 arcmin = 2.909 · 10⁻⁴ rad

The larger the effective radius, the greater the impact that the same torsional backlash has on positioning accuracy—which is why the same arcminute specification may be harmless on a short lever but unacceptable on a long boom.

Backlash-free and backlash-prone components

Backlash-free to low-backlash: Precision planetary gearboxes (typically ≤ 1–3 arcmin, manufacturing quality per DIN 3961/3962; internationally ISO 1328-1, though the grades there are only approximately comparable), bellows couplings (< 1 arcmin), and preloaded bearings/guides—though these are 2 to 5 times more expensive than standard components.

Subject to backlash: Worm gearboxes (5–20 arcmin new, 20–50 arcmin after several years), jaw couplings with elastomer inserts (3–8 arcmin), and standard racks per DIN 8 (10–30 arcmin)—more than sufficient for material handling and force-controlled applications.

Mnemonic

Always convert the torsional backlash to the actual effective radius in millimeters before determining a backlash class—the same value in arcminutes is acceptable for a 50-mm lever but unacceptable for a 1-meter boom.

Worked example

Given

Effective radius R = 200 mm; torsional backlash φ = 5 arcmin.

Calculation

  • φ = 5 · 2.909 · 10⁻⁴ = 1.45 · 10⁻³ rad
  • s ≈ 200 mm · 1.45 · 10⁻³ ≈ 0.29 mm

A backlash-free axis (< 1 arcmin) reduces the same error to less than 0.06 mm.

Knowledge check

Answer all three questions, then click "Check". From 2 of 3 correct answers, the unit counts as completed. You can retry at any time.

This feature needs JavaScript. You can still read the learning content without JavaScript.

Question 1 of 3: According to the learning unit, at what torsional backlash does a component count as “backlash-free”?
Explanation

The guide sets the threshold for “backlash-free” at less than 1 arcminute (arcmin); values below 0.5 arcmin are already considered high precision.

Source: Zero Backlash vs. Backlash →
Question 2 of 3: A lever arm of R = 150 mm has a torsional backlash of φ = 8 arcmin. What is the linear positioning error s in mm (1 arcmin = 2.909 · 10⁻⁴ rad)?
mm
Explanation

s ≈ R · φ = 150 mm · 8 · 2.909 · 10⁻⁴ ≈ 0.35 mm.

Source: Zero Backlash vs. Backlash →
Question 3 of 3: According to the learning unit, which component typically has 5–20 arcmin of torsional backlash when new?
Explanation

Due to the sliding contact between the worm and the gear, worm gearboxes have 5–20 arcmin of torsional backlash when new, which can increase to 20–50 arcmin after several years of operation.

Source: Zero Backlash vs. Backlash →

Please answer all three questions to activate "Check".

Further reading (optional)

Guide: Zero Backlash vs. Backlash (opens in a new tab)

Learning purpose: calculation methods and figures are simplified teaching examples. For a real machine, the manufacturer’s specifications, the relevant standards and a check by a qualified person apply.

Curriculum v0.1 (Beta) · Status 17.09.2026 · content carefully prepared and reviewed – final sign-off to follow

+49 [40] 5388921-11 sales@tea-hamburg.de