The Holroyd 4EX-R-BL can mill helical rotors of up to 450 mm in diameter and will rough mill blower blanks of around 320 mm in diameter and 900 mm body length. In the latter case it can produce straight-fluted rotors in 30 minutes floor-to-floor, ready for finish profile milling to size, representing a massive saving on the one-and-a-half to two hours typically required to cut individual Roots-type blower rotor flutes using traditional milling techniques.

Says Holroyd sales manager Mark Curran: “Until now, manufacturers producing rotors for Roots-type blowers have been forced to either rely on NC flat-bed milling machines or machining centres that have been retrofitted to absorb the considerable vibrations that occur during the flute milling process. Consider the fact that, when using either one of these methods, each flute has to be milled in a separate operation, and it’s not surprising that the machining process for Roots-type rotors has always been labour-intensive and costly.

“By contrast, the technology offered by the 4EX-R-BL moves the manufacture of Roots-type rotors away from traditional flat-bed milling, where the component would be manually turned after each flute was cut, to a fully automated, programmable process able to machine both two- and three-flute blowers in one sequence.”

Totally removing the need for manual intervention or indexing during the milling of each flute, the Holroyd 4EX-R-BL features a bespoke steadying system that has been designed to withstand the additional forces that are generated during the milling of straight flutes. Specially developed ‘finger clamps’ ensure the workpiece is held securely while a flute is being milled, then release to enable automatic rotation and positioning ready for milling of the next flute.

The Holroyd 4EX-R-BL, at-a-glance:


  • Maximum workpiece diameter:Rotor 450mm / Blower 320mm
  • Minimum workpiece diameter: Rotor 100mm / Blower 100mm
  • Maximum component weight: 900kg
  • Maximum (overall) component length (incl. chuck): 1,820mm
  • Maximum work traverse: 1,600mm
  • Cutter head

  • Equipped for cutting with Tungsten Carbide and HSS tooling systems
  • Maximum cutter width: Rotor 160 mm /Blower 320 mm
  • Cutter arbor interface: HSK160
  • Cutter speed (infinitely variable, unidirectional): 20 – 250 rpm
  • Maximum torque at cutter spindle @ 105 rpm: 600Nm
  • Maximum Head Angle: +90 /- 55°
  • CNC control

  • Fanuc 31i-series 4-axis CNC system with Macro ‘B’ programming