Cylindrical and Internal Grinders Wheelheads Belt Drive High-Frequency motor Drive Workheads
17-50 8-50 Wide Range
Up to 100,000 10,000-150,000 Up to 5,000
Oil mist- grease-oil Oil mist- grease Grease
100-120 95-120 95-110
Surface Grinders Tool and Cutter Grinders Gear and Thread Grinders
Wide Range 20-35 60-80
1,800-6,000 5,000-10,000 3,000 - 5,000
Grease Grease Grease
110 100-115 100-115
Boring Heads Jig Bores Lathes
Wide Range 25-75 Wide Range
Up to 10,000 Up to 3,000 Up to 10,000
Oil mist-grease-oil Grease Oil-grease
105-120 85-100 100-120
Drilling Machines Milling Machines Routers
15-40 Wide Range 20-60
Up to 30,000 Up to 12,500 12,000-30,000
Oil-grease Oil mist-grease-oil Oil mist-grease
100-115 100-115 110-125
MAINTENANCE • MACHINE TOOL SPINDLES
In their efforts to attain even smoother and finer surface finishes, many users of high-speed wheelheads, especially of the belt driven type, operate their spindles at higher speeds than those for which they were designed. Spindle failure often occurs due to the rise in operating temperature caused by the breakdown of the lubricant, and because the original spring preload on the bearings was not reduced to correspond with that recommended for the increased speed. In such cases, the induced heat expands the internal parts of the spindle, thereby tightening the mounting fits and preventing the floating of spring loaded bearings from moving axially. Thus, additional heat is generated and failure results. Wheelhead users are cautioned to consult the original equipment manufacturer when increased speeds for their spindles are contemplated.
Many factors are involved in the design, fabrication and use of high speed spindles. Among them are the selection of the ball bearings, the amount of applied preloading, the mounting fits, the accuracy of the parts and the skill with which they are assembled, the operating temperature and speed involved, and lastly, the type of lubricant - grease, oil, or oil mist. Adequate lubrication, low operating temperatures, accurate and smooth operation, low friction, and a high degree of axial and radial rigidity are all extremely important qualities for successful machine tool spindle performance. The attainment of these qualities will continue to require the cooperation of the ball bearing manufacturer and the machine tool builder, as well as the machine tool user.
TYPICAL APPLICATIONS OF BALL BEARINGS TO MACHINE TOOL SPINDLES
Bearing Bore, mm
Speed Range, rpm
Approximate Operating Degrees F.
In taking corrective measures it is important to know the operating history of the spindle and to study a cross-sectional drawing of the mounting arrangement. This information should include the following:
Operational speed Operating temperature Type of lubrication Estimate of working loads Type of drive and horsepower Material processed Reason for spindle failure
Typical applications of precision ball bearings to machine tool spindles, showing bearing bore sizes, speed range, type of lubrication and approximate operating temperature, are tabulated at the bottom of this page.
In addition and before the spindle is disassembled, the runout of the spindle nose should be determined with a 0.0001 inch indicator and recorded. The bearings should be removed carefully, without further damage, and tagged 1, 2, 3, 4, etc. starting from the work-end of the spindle. Pairs of bearings should be marked DB, DF or DT to denote whether the bearings had been mounted back-to-back, face-to-face, or in tandem. The conditions of the bearings should be noted for the entry of foreign matter, lack of lubrication, excessive temperatures and the extent of damage.
Before bearing replacement is made, the spindle parts should be thoroughly cleaned with Varsol and measured carefully for wear in the housing bores and shaft seats. Housing and shaft shoulders should be checked for equal lengths and parallelism of faces. All mating parts should be free of nicks and burrs.