Tunnel bores in gearbox housings

Machining large tunnel bores in gearbox housings with several diameters and close tolerances

Machining task

The tunnel bores are stepped and often have 6 to 8 different diameters in the range from 160 to 290 mm. The bores are required to have high concentricity in relation to each other with ø tolerances from IT7 to IT9 at the same time. Furthermore, this housing is to be machined on a standard machine.


Tools for machining these large diameters are very heavy, particularly if several steps are to be machined at once. As standard machines are mostly only able to change a tool weight of max. 20 kg, the machining is normally distributed over several tools. This situation signifies long machining times that comprise the individual productive times and the non-productive times, which depend on the number of tools. In addition, the usage of several tools makes compliance with the concentricity requirements extremely difficult.

Our solution

Using a specially designed lightweight tool it is possible to combine all the diameters to be machined on one tool and to keep within the total weight allowed for tool changes on standard machines. The individual sections are equipped with inserts and guide pads. The pads support the tool during the machining and contribute to the quiet running of the tool despite the long projection length.

MAPAL Effect

The result of this unique machining solution is a significant time saving with a simultaneous improvement in quality. Depending on the housing and the number of features to be machined, the machining time is reduced by up to 80 %. The increase in productivity and the related cost savings are correspondingly high. The requirements for the concentricities and surface finishes are significantly bettered. This aspect provides process reliability and part quality.

  • Reduction of the machining time by up to 80 %
  • Increase in productivity
  • Significant increase in the machining quality
  • High process reliability

Joachim Vaas

Phone: +49 7361 / 585 - 1216

E-Mail: joachim.vaas(at)de.mapal.com

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