Alongside the mounting of the feed spindle and the rotary table, as well as the guides on the work table, the mounting of the main spindle is one of the most important components in the machine tool and is responsible for accepting and transferring the forces.
The spindle mounting must fulfil the requirements for machine tools. These can be expressed as high working accuracy and high performance over an extended period of time, with low manufacturing and operating costs.
In order to fulfil these requirements, spindle mountings have the following features:
- Exact positioning with low feed forces through low friction and low stick-slip
- Compliance with the accuracy over an extended period of time through low wear and resistance to being abraded
- Low positional changes of the components being fed, due to a high degree of stiffness and lack of play
- Avoidance of the machine tool chattering through good damping in supporting and movement directions
Based on their physical principle or the type of lubrication, the build-up of the lubricating film or the build-up of force, spindle mountings are subdivided as follows:
- Roller bearing
Roller bearings represent the most commonly used bearing system for spindle mountings. The multitude of positive characteristics of the bearing, particularly the international standardisation, the relatively simple calculation and the simple selection by means of catalogues, are responsible for this development. Each type of mounting is primarily suitable only for one characteristic area of application. This is explained through the different fulfilment of the application requirements for strength, stiffness, axial angular adjustment, increased guidance accuracy and high rotational speeds. In general, roller bearings are able to bear greater loads than ball bearings of the same size. On the other hand, roller bearings are less able to deal with combined radial and axial loads and the speed limits than ball bearings. As a result, spindle bearings were developed specially for machine tool construction. These were able to meet the requirements profile for higher concentricity and stiffness as well as lower friction moments.
In combination with the spindle bearings, cylindrical roller bearings can be used as floating bearings, which avoids the requirement for an elaborate design of the floating bearing mounting point. Furthermore, cylindrical roller bearings also exhibit higher radial stiffness due to their larger contact surfaces, but are nonetheless restricted to a maximum rotational speed of approx. 1.0 x 106 mm/min. [WECK2]
The arrangement of the roller bearings can be subdivided into three basic arrangements:
- Fixed-floating arrangement
- Fixed-fixed arrangement
- Sprung arrangement