MAINTENANCE • MACHINE TOOL SPINDLES
Enclosed Dust-Free Working Area
Machine tools must meet the ever-increasing demands of modern industry for faster speeds, greater accuracy, smoother finishes and higher production rates at minimum costs. Such considerations are primarily influenced by the machine tool spindle with its superprecision ball bearings; and the machine tool builder, the spindle maker, and the ball bearing manufacturer are all making great advances in the achievement of these goals.
The machine tool spindle is expertly designed. It is fabricated from the best materials with the utmost care. Quality and accuracy of machining and the rate of production depend greatly on the ball bearings that support the spindle. Spindle maintenance and servicing have become a matter of prime importance and be done only by expert assemblers in meticulously clean, well-lighted and constant temperature surroundings.
The desired results in the maintenance of machine tool spindles are achieved by an experienced mechanic working in a well organized, clean, and enclosed area set apart from the manufacturing processes or machines that propagate dust-laden air. His work bench and tools are clean and maintained in good working order. His surface plate is equipped with bench centers or parallel V-blocks and weighted end block, and test gage-blocks with 0.0001 inch dial indicators. He is equipped with outside and inside micrometers, a hole gage with 0.0001 inch indicator, a comparator gage with 0.0001 inch indicator and master discs and rings or precision blocks.
To insure dimensional accuracy and proper fitting of the spindle parts and ball bearings, all checking and assembly operations should be performed with gages, parts, and bearings that have attained a constant temperature. The equipment and all the parts to be assembled should be held in the working area long enough for them to assume thermal equilibrium before any measurements are taken.
In this section the basic principles involved in the proper maintenance of machine tool spindles are outlined. Although the servicing of a permanently grease-lubricated belt-driven internal grinding wheelhead, Figure 1, is described, the mounting techniques and installation procedures are typical for almost all types of ball bearing spindles.
Inspection of Parts before Assembly
The ideal shaft bearing seat is accurately and smoothly ground and absolutely free from burrs, tool marks and rust. An indicator gage that reads 0.0001 inch is used to check the bearing seat. This gage is set to the basic diameter with a master disc or with precision blocks. Deviations from the standard dimension are indicated by rolling the shaft back- ward and forward in several positions, and an axial movement of the bearing seat under the indicator gage registers any taper.
Figure 1 – Internal Grinding Wheelhead