Machinery's Handbook, 31st Edition
GRINDING WHEELS 1303 Size Selection Guide for Single-Point Truing Diamonds.— There are no rigid rules for determining the proper size of the diamond for any particular truing application because of the very large number of factors affecting that choice. Several of these factors are re- lated to the condition, particularly the rigidity, of the grinding machine and truing device, as well as to such characteristics of the diamond itself as purity, crystalline structure, etc. Although these factors are difficult to evaluate in a generally applicable manner, the expected effects of several other conditions can be appraised and should be considered in the selection of the proper diamond size. The recommended sizes in Table 3 must be considered as informative only and as repre senting minimum values for generally favorable conditions. Factors calling for larger diamond sizes than listed are the following: Silicon carbide wheels (Table 3 refers to aluminum oxide wheels) Dry truing Grain sizes coarser than No. 46 Bonds harder than M Wheel speed substantially higher than 6500 sfm (1981 m/min). It is advisable to consider any single or pair of these factors as justifying the selection of one size larger diamond. As an example: for truing an SiC wheel, with grain size No. 36 and hardness P, select a diamond that is two sizes larger than that shown in Table 3 for the wheel size in use. Table 3. Recommended Minimum Sizes for Single-Point Truing Diamonds
Examples of Max. Grinding Wheel Dimensions (inches) Diameter Width
Diamond Size in Carats a
Index Number (Wheel Dia. 3 Width, Inches)
0.25 0.35 0.50 0.60 0.75 1.00 1.25 1.50 1.75 2.00 2.50 3.00 3.50 4.00
3 6
4 6 8
0.75
1
10 15 21 30 48 65 80
1.25 1.50 1.75 2.50 3.50 4.00 4.00 5.00 6.00 8.00 8.00
10 12 12 14 16 20 20 24 24 30 36
100 150 200 260 350
10.00
a One carat equals 0.2 gram. Single-point diamonds are available as loose stones, but are preferably procured from specialized manufacturers supplying the diamonds set into steel nibs. Expert setting, com prising both the optimum orientation of the stone and its firm retainment, is mandatory for assuring adequate diamond life and satisfactory truing. Because the holding devices for truing diamonds are not yet standardized, the required nib dimensions vary depending on the make and type of different grinding machines. Some nibs are made with angular heads, usually hexagonal, to permit occasional rotation of the nib either manually, with a wrench, or automatically.
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