Twist Testing

STT Shaft Twist Tester

Twist Testing – Optical, Without Thread and Profilometer

The STT Shaft Twist Tester is a system designed for quickly testing of twist structures and/or twist-freed condition on shafts in seconds.

Product Description

The sealing function of a shaft seal is determined in essence by the twist of the shaft surface. Once twist is present, a critical micro-pumping effect begins as the shaft rotates, causing fluid leakage or component wear. The STT Shaft Twist Tester can be used to precisely visualize these twist structures. Optical filtering indicates the presence of twist on the surface of the sample and allows the twist parameters, twist depth, and period length to be estimated. The number of diffraction fringes shown here represents a measure of the twist depth, and their spacing a measure of the period length.

Optical diffraction can reveal twist structures with amplitudes well below the roughness amplitudes of the sealing surface. This allows quality control to be performed quickly and reliably in the immediate vicinity of the machining process, typically in twist-free grinding or turning processes.

Design & Function

With test times in the second range, the instruments can be used in a variety of ways, such as incoming inspection, process optimization of the manufacturing process, or complete (quality) control in series production.

In the past, the only way to image twist structures was to use sophisticated and costly tactile measurement technology. The long measurement time and restrictive measurement conditions meant it was impossible to carry out a near-production test. Alternatively, the thread method is used, but this depends on various constraints (e.g., thread material, thread thickness, attached weight, or lubricant viscosity). However, the main disadvantage of the thread method is that it has been shown to fail with very small or very large twist structures.

In the case of the STT, a test instrument has been developed that combines secure testing for absence of twist with a high level of user friendliness. The STT hand-held device is placed on the test sample. The operator can immediately detect the presence of twist structures on the surface of the manufactured part using a system of stripes in the field of view.

STT Shaft Twist Tester Variants

STT Shaft Twist Tester NO

Twist Test – Analogue and Fast

  • Production-related twist testing
  • Quickly operational
  • Built-in magnifying glass
  • Test result immediately visible
Product request

STT Shaft Twist Tester NK

Twist Testing With a Digital Camera

  • Adapted digital camera
  • Production-related twist testing
  • Evaluation and archiving software
  • Test result readable on camera display
Product request

STT Shaft Twist Tester NV

Twist Testing with a Video Camera

  • Production-related twist testing
  • Dynamic PC-based display
  • Adapted video camera
  • Ideal for 100% control
Product request

Product Highlights

  • Direct visualization of the twist structures
  • Robustness for direct use in production
  • Compact design


  • No additional test media required
  • Quick results
  • Easy to use

Technical Specifications

  • Measuring range: DP: 20 – 500 μm
  • Twist depth: Dt > 200 nm*
  • Axial support length: 15 mm
  • Shaft diameter: 5 – 300mm
  • Light source: Class 2 laser diode module
  • Power supply: 6 volt battery
  • Weight: approx. 600 g
  • Camera-aided documentation (optional)

* Depending on roughness and twist period, permissible roughness Ra = 0.1-0.5 µm

Application Areas

  • For twist-free grinding and precision turning processes
  • Quality control, quality assurance, and production optimization of shafts and cylindrical components in general
  • Quality control and assurance of shafts and cylindrical components, documentable for quality management systems (STT Shaft Twist Tester NK)
  • Quality control on the test stand for twist detection on shafts and other cylindrical components (STT Shaft Twist Tester NV)
  • Testing on, e.g.: crankshafts, transmission shafts, bearing sealing surfaces, etc.



STT Shaft Twist Tester

(6.8 MiB)