Machinery's Handbook, 31st Edition
1338 HONING PROCESS fast because the dressing action on the grits will be severe; and 4) To improve the finish, use a finer abrasive grit, incorporate more multi-direction action, allow more “run-out” time after honing to size, or increase the speed of rotation. Possible Adjustments for Eliminating Undesirable Honing Conditions
Adjustment Required to Correct Condition a Abrasive b Other
Undesirable Condition
Abrasive Glazing Abrasive Loading
+ 0 0 − + 0
+ + + + +
0
− − − −
− − −
+ + +
0 0
− −
− −
− −
Too Rough Surface Finish Too Smooth Surface Finish Poor Stone Life Slow Stock Removal Taper — Large at Ends Taper — Small at Ends
0 + + + +
+ + + 0
− − − + + + − − − + + + + +
0
− − − −
− − −
+
+ +
+ 0 0
0 0
− −
− 0 0
− −
0 0
0 0
0 0
0 0
0 0
0
−
0 0 + a The + and + + symbols generally indicate that there should be an increase or addition while the − and − − symbols indicate that there should be a reduction or elimination. In each case, the double sym- bol indicates that the contemplated change would have the greatest effect. The 0 symbol means that a change would have no effect. b For the abrasive adjustments the + and + + symbols indicate a more friable grain, a finer grain, a harder grade or a more open structure and the − and − − symbols just the reverse. Compiled by Micromatic Hone Corp. Surface roughnesses ranging from less than 1 micro-inch rms (0.0254 μ m rms) to a relatively coarse roughness can be obtained by judicious choice of abrasive and honing time but the most common range is from 3 to 50 micro-inches rms (0.0762 − 1.27 μ m rms). Adjustments for Eliminating Undesirable Honing Conditions.— The accompanying table indicates adjustments that may be made to correct certain undesirable conditions encountered in honing. Only one change should be made at a time and its effect noted before making other adjustments. Tolerances.— For bore diameters above 4 inches (101.6 mm) the tolerance of honed surfaces with respect to roundness and straightness ranges from 0.0005 to 0.001 inch (0.0127 −0.0254 mm); for bore diameters from 1 to 4 inches (25.4 −101.6 mm), 0.0003 to 0.0005 inch (0.0076 −0.0127 mm); and for bore diameters below 1 inch (25.4 mm), 0.00005 to 0.0003 inch (0.0013 −0.0076 mm). Laps and Lapping Material for Laps.— Laps are usually made of soft cast iron, copper, brass or lead. In gen eral, the best material for laps to be used on very accurate work is soft, close-grained cast iron. If the grinding, prior to lapping, is of inferior quality, or an excessive allowance has been left for lapping, copper laps may be preferable. They can be charged more easily and cut more rapidly than cast iron, but do not produce as good a finish. Whatever material is used, the lap should be softer than the work, as, otherwise, the latter will become charged with the abrasive and cut the lap, the order of the operation being reversed. A common and inexpensive form of lap for holes is made of lead which is cast around a tapering steel arbor. The arbor usually has a groove or keyway extending lengthwise, into which the lead flows, thus forming a key that prevents the lap from turning. When the lap has worn slightly smaller than the hole and ceases to cut, the lead is expanded or stretched a little by the driving in of the arbor. When this expanding operation has been repeated two or three times, the lap usually must be trued or replaced with a new one, owing to distortion.
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