. Canadian foundryman (1918). esswas 1650 pounds per square inch, thegrade K at 1750 pounds per square inch,and so on. Therefore, one might inferthat all grade J wheels would burstwhen this same stress was an Exact Value Now let us see what really hap-pens when several wheels of sup-posedly the same grade are find that those that have beendetermined to be of grade J hard-ness will burst at stresses ranging from1600 to 1700 pounds per square inch,grade M at from 1880 to 1790 pounds persquare inch and so on. In other words,a grade represents a range of values be-tween defin
. Canadian foundryman (1918). esswas 1650 pounds per square inch, thegrade K at 1750 pounds per square inch,and so on. Therefore, one might inferthat all grade J wheels would burstwhen this same stress was an Exact Value Now let us see what really hap-pens when several wheels of sup-posedly the same grade are find that those that have beendetermined to be of grade J hard-ness will burst at stresses ranging from1600 to 1700 pounds per square inch,grade M at from 1880 to 1790 pounds persquare inch and so on. In other words,a grade represents a range of values be-tween definite limits. An understandingof this point is most essential to theusers of grinding wheels and will explainmany seeming variations in grindingwheel action and life. Assume a certain snagging operationis being performed, whereby all the fac-tors combine to bring a pressure against have a longer life than one not so con-stituted. This last wheel will not bebonded strong enough to withstand thegrinding1 forces and will wear away. FIG. 1. CHIPS FROM WORK GROUND WITH AN UNSUITABLE WHEEL UNDER IMPROPER CONDITIONS. quite rapidly, in fact, much more rapidlythan the difference in strength or hard-ness would seem to warrant. This pointhas been developed in detail because anunderstanding of it will eliminate manyquestions arising between the wheelmanufacturer and the wheel is needless to say that there is aclose limit to the allowable variation andthe manufacturer who best keeps withinthese limits, deserves the greatest con-fidence of the consumer. The old idea of grinding considered itas a wearing down of the metal by rub-bing or friction. This is now our under-standing of the lapping process andmodern grinding has progressed far be-yond this point. However, if a wheelis bonded too hard for the work at hand, LEGEND -A *NOLOAD B*POW£RCONSUi1ED QyShaRP CuTTINGPOlNTSOFNEWLYDRESSEDWHEEL. C- Cutting Points Beginning to Dull. D-GlazeoCondition-Less3iT£ano Friction.^•Loading -In
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