Elastic shafts (TM625)

investigation of the natural modes of various shafts with continuous mass distribution and of a Laval rotor



  • The terms “critical speed” and “resonance” are often used when referring to rotating systems.
  • Resonance occurs when the natural frequency and the excitation frequency match.
  • The natural frequency of an oscillatory system is that frequency at which the system oscillates with the associated natural mode after a single excitation.
  • Operation at critical speed can damage the system because of the high vibration amplitudes.
  • In order to study the phenomenon of shaft vibration in more detail, there are two simplified calculation models.
  • In the first case, the mass of the elastic shaft is evenly distributed along its length.
  • In the second case, the shaft consists of massless, elastic shaft sections and the masses are combined into discrete mass disks.
  • The TM 625experimental unit can be used to study the natural modes of these different models.
  • Illustrative experiments are used to explain resonance and the supercritical or subcritical states of a vibrating system.
  • Six shafts of different lengths and diameters are available.
  • The shafts can be mounted on four self-aligning ball bearings and fitted with a mass disk to construct a Laval rotor.
  • The axial positions are read on a scale mounted parallel to the shaft.
  • A three-phase motor drives the shaft via a flexible coupling.
  • The electronically controlled speed can be selected via two potentiometers and is continuously variable.
  • It is displayed digitally.
  • A transparent protective cover and safety bearing ensure safe operation.
  • The measured values can be displayed and analysed on a PC using the optional TM 620.20unit for data acquisition.

Technical Details:


  • experimental unit for determining critical speeds and investigating the natural modes of a shaft
  • 6 high-tensile steel shafts
  • up to 4 self-aligning ball bearings, each moveable to any point as a shaft bearing
  • 1 mass for constructing a Laval rotor
  • 3 safety bearings and transparent protective cover for safe operation
  • three-phase motor: 2 pre-selectable speed ranges; speed electronically controlled and continuously adjustable
  • digital speed display
  • system TM 620.20 for data acquisition available as an option

Technical Data:

  • 6 shafts
    • Ø 3mm, 6mm, 7mm
    • L: 600mm, 900mm
    • high-tensile steel
  • Mass, disk-shaped
    • Ø 80mm
    • m: 965g
    • high-tensile steel
  • Motor
    • power: 0,25kW
    • speed: 6000min-1
    • speed electronically controlled
  • Shaft bearing
  • 4x self-aligning ball bearings
  • 3x safety bearings
  • Measuring ranges
  • speed: 0…6000min-1
  • scale for clearance measurement: 0…1000mm
  • 230V, 50Hz, 1 phase
  • 230V, 60Hz, 1 phase; 120V, 60Hz, 1 phase
  • UL/CSA optional

Dimensions & Weight:

  • L x W x H: 1550x380x450mm
  • Weight: approx. 65kg

Learning Objectives/Experiments:

  • investigation of a Laval rotor:
    • critical speed
    • self-alignment
  • natural modes on a shaft with continuous mass distribution with:
    • different bearing clearances
    • different shaft diameters
    • different shaft lengths

Scope of Delivery:

  • 1 experimental unit
  • 6 shafts
  • 1 set of tools
  • 1 set of instructional material


  • optimal visibility and simultaneous protection thanks to transparent protective cover


Due to the continuous development of our products, the goods supplied may vary in detail to that illustrated on this Website.