ABRASIVE CUTTING Probable Causes of Cutting-Off Difficulties Machinery's Handbook, 31st Edition
1336
Difficulty
Probable Cause
(1) Inadequate clamping which allows movement of work while the wheel is in the cut. The work should be clamped on both sides of the cut. (2) Work vise higher on one side than the other causing wheel to be pinched. (3) Wheel vibration resulting from worn spindle bearings. (4) Too fast feeding into the cut when cutting wet. (1) Insufficient power or drive allowing wheel to stall. (2) Cuts too heavy for grade of wheel being used. (3) Wheel fed through the work too slowly. This causes a heating up of the material being cut. This difficulty encountered chiefly in dry cutting. (1) Too rapid cutting when cutting wet. (2) Grade of wheel too hard for work, resulting in excessive heating and burning out of bond. (3) Inadequate coolant supply in wet cutting. (4) Grade of wheel too soft for work. (5) Worn spindle bearings allowing wheel vibration. (1) Feeding too slowly when cutting dry. (2) Grit size in wheel too coarse. (3) Grade of wheel too hard. (4) Wheel too thick for job.
Angular Cuts and Wheel Breakage
Burning of Stock
Excessive Wheel Wear
Excessive Burring
Honing Process The hone-abrading process for obtaining cylindrical forms with precise dimensions and surfaces can be applied to internal cylindrical surfaces with a wide range of diameters such as engine cylinders, bearing bores, pin holes, etc. and also to some external cylindrical surfaces. The process is used to: 1) eliminate inaccuracies resulting from previous op- erations by generating a true cylindrical form with respect to roundness and straightness within minimum dimensional limits; 2) generate final dimensional size accuracy within low tolerances, as may be required for interchangeability of parts; 3) provide rapid and economical stock removal consistent with accomplishment of the other results; and 4) gen- erate surface finishes of a specified degree of surface smoothness with high surface quality. Amount and Rate of Stock Removal.— Honing may be employed to increase bore diam eters by as much as 0.100 inch (2.5 mm) or as little as 0.001 inch (0.25 mm). The amount of stock removed by the honing process is entirely a question of processing economy. If other operations are performed before honing then the bulk of the stock should be taken off by the operation that can do it most economically. In large diameter bores that have been distorted in heat treating, it may be necessary to remove as much as 0.030 to 0.040 inch (0.76–1.02 mm) from the diameter to make the bore round and straight. For out-of-round or tapered bores, a good “rule of thumb” is to leave twice as much stock (on the diameter) for honing as there is error in the bore. Another general rule is: For bores over 1 inch (25.4 mm) in diameter, leave 0.001 to 0.0015 inch stock per inch of diameter (0.025–0.038 mm stock/mm). For example, 0.002 to 0.003 inch (0.05–0.08 mm) of stock is left in 2-inch bores (50.8 mm) and 0.010 to 0.015 inch (0.25–0.38 mm) in 10-inch (254 mm) bores. Where parts are to be honed for finish only, the amount of metal to be left for removing tool marks may be as little as 0.0002 to 0.015 inch (0.005–0.38 mm) on the diameter. In general, the honing process can remove stock from bore diameters at the rate of 0.009 to 0.012 inch per minute (0.23–0.30 mm/min) on cast-iron parts and from 0.005 to 0.008 inch per minute (0.13–0.20 mm/min) on steel parts having a hardness of 60 to 65 RC (Rockwell C scale). These rates are based on parts having a length equal to three or four times the diameter. Stock has been removed from long parts such as gun barrels, at the rate of 65 cubic inches per hour (17.75 cc/s). Recommended honing speeds for cast iron range from 110 to 200 surface feet per minute (34–61 m/min) of rotation and from 50 to 110 lineal feet per minute (15–34 m/min) of reciprocation. For steel, rotating surface speeds range from 50 to 110 feet per minute (15–34 m/min) and reciprocation speeds from 20 to 90 lineal feet per minute (6–27 m/min) . The rotation and reciprocation speeds to be used depend on the size of the work, the amount and characteristics of the material to be removed, and the
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online