Machinery's Handbook, 31st Edition
1302 GRINDING WHEELS producing fine finishes. Such variations, however, must always stay within the limits set by the grain size of the wheel. Thus, the advance rate of the truing diamond per wheel revolution should not exceed the diameter of a grain or be less than half of that rate. Consequently, the diamond crossfeed must be slower for a large wheel than for a smaller wheel having the same grain size number.Typical crossfeed values for frequently used grain sizes are given in Table 2.
10 – 15
C L
10 – 15
" – "
1 8 1 4
(3.175–6.35 mm)
CROSSFEED
Table 2. Typical Diamond Truing and Crossfeeds
Crossfeed per Wheel Rev.
Crossfeed per Wheel Rev.
Grain Size
inch
mm
Grain Size
inch
mm
30 36 46
0.014–0.024 0.35–0.61 0.012–0.019 0.30–0.48 0.008–0.014 0.20–0.35 0.007–0.012 0.18–0.30
60 80
0.006–0.010 0.15–0.25 0.004–0.007 0.10–0.18
120 0.0025–0.004 0.06–0.10
50 … These values can be easily converted into the more conveniently used inch-per-minute units, simply by multiplying the crossfeed rate in inches by the rpm of the grinding wheel. Example: For a 20-inch diameter wheel, Grain No. 46, running at 1200 rpm: Crossfeed rate for roughing-cut truing, approximately 17 ipm; for finishing-cut truing, approxi mately 10 ipm. Coolant should be applied before the diamond comes into contact with the wheel and must be continued in generous supply while truing. … … The speed of the grinding wheel should be at the regular grinding rate, or not much lower. For that reason, the feed wheels of centerless grinding machines usually have an additional speed rate higher than functionally needed, that speed being provided for wheel truing only. The initial approach of the diamond to the wheel surface must be carried out carefully to prevent sudden contact with the diamond, resulting in penetration in excess of the selected depth of cut. It should be noted that the highest point of a worn wheel is often in its center portion and not at the edge from which the crossfeed of the diamond starts. The general conditions of the truing device are important for best truing results and for assuring extended diamond life. A rigid truing spindle, well-seated diamond nib, and firmly set diamond point are mandatory. Sensitive infeed and smooth traverse movement at uniform speed also must be maintained. Resetting of the diamond point. Never let the diamond point wear to a degree where the grinding wheel is in contact with the steel nib. Such contact can damage the setting of the diamond point and result in its loss. Expert resetting of a worn diamond can repeatedly add to its useful life, even when applied to lighter work because of reduced size.
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