MAINTENANCE • MACHINE TOOL SPINDLES
The locknut is removed from the assembly and the line transferred to its front face. This procedure locates the area to be scraped or lapped.
Scraping may be done with a scraping tool on the high surface and approximately 90 on both sides. Care should be taken to scrape evenly and uniformly. The depth of scraping (which will always be slight) can be judged only by the amount of runout shown on the indicator dial.
When the estimated amount of metal has been removed by scraping, the locknut is washed and blown clean. It is then placed against the face of the front slinger and tightened. New readings are taken, and if the runout persists, the locknut is removed and scraped in the same manner. If scraping on the same surface area is necessary, it is obvious that not enough metal was removed the first time. If the high surface is diagonally opposite, too much metal was removed. Scraping is continued until the face shows a very close reading on the indicator. To determine and correct any inaccuracies that might exist at the drive-end of the spindle, indicator readings are taken at point Y, Figure 1. After locknut S is loosened clockwise and removed, the same basic procedures used for the wheel end of the spindle are followed. The wheelhead assembly is then ready for the run-in test and final inspection.
Checking Temperature, Vibration and Roughness
Before starting the test run for final inspection, the spindle is started and stopped a few times to make sure the wheelhead and testing equipment are in good working order. The spindle is then brought up to operational speed, which should not exceed the maximum speed indicated on the nameplate.
Temperature readings are taken as close to the bearings as possible, every five minutes at first, for each bearing on the housing. If the wheelhead heats up rapidly, it is stopped, allowed to cool to room temperature, and then re-started. Readings are then taken about every fifteen minutes until the temperature levels off, The wheelhead should not be permit- ted to run hotter than 50 above room temperature or to run so that the heat becomes unbearable to the touch. Generally, temperature readings of more than 120F are not encoun- tered. Three to four hours should be reasonable time for running-in the wheelhead and checking for temperatures, unusual sounds, vibration, and roughness. Following the successful completion of this test, the precision-built wheelhead is ready for use in the manufacturing area.
Elaborate precautions are taken to insure that superprecision ball bearings are dirt-free and thoroughly protected when packaged. Extreme care should be exercised to keep them clean and away from moisture and contamination from the time they are unpackaged until they are mounted in spindles and running.
In servicing machine tool spindles, cleanliness cannot be overemphasized. THe work area, bench and tools should be clean and well organized. Clean hands are necessary, too. Plenty of clean lint-free rags should be available to keep the hands free of moisture, grime and dust-gathering oil. The spindle parts should be washed thoroughly in cleaning solution and dried with a filtered air under pressure.In addition to the spindle parts, the inside of the housing and all oil holes and threads should be solvent cleaned and air dried. Any corrosion on the shaft should be carefully removed. This is done by stoning or with crocus cloth while rotating the shaft and must be done carefully to avoid polishing the shaft undersize. These operations are followed with solvent cleaning and air drying.
Varsol with a 10% oil mixture is a good grade of non- flammable cleaning solution and an excellent cleansing agent. Chlorinated solvents such as tetrachloride are definitely not recommended for this purpose.
Freshly unpackaged bearings that are to be in oil or oil mist lubricated in spindles need not be cleaned of their protective oil. Bearings that are grease packed at our factories should be used as received.
Often times, the user packs bearings with grease prior to mounting. In such cases, the original protective oil slush is removed from the bearings with Varsol, and the bearings are dried with air under pressure by holding the bearing firmly so that spinning is avoided. Clean grease of the correct type should be packed carefully into the bearings in recommended quantities.