Smithy GN1300 - Manual (Page 110)

Materials other than Steel
As pointed out earlier,when grinding HSS cutters, we determine cutting angles primarily
by strength requirements, not keenness requirements. Angles and rakes for general
industrial shops use are established. In machining steel, the softer the steel, the keener
the angle of the cutting edge. For soft steels, angles as acute as 61° are possible (Figure
A.5).
The same general rule applies to cast iron. Chilled or very hard cast iron requires tools
with cutting-edge angles as great as 85°. For ordinary cast iron, you obtain greatest
efficiency with a more accurate cutting edge – approximately 71° (Figure A.6).
Figure A.3 Grinding sequence for an unground cutter bit
Figure A.4 When honing, draw the cutter away
from the cutting edge across the oilstone
Figure A.5 With soft steels, 61° angles are possible
Figure A.6 With cast iron, a 71° angle is most efficient
Granite 1300 Series Operator’s Manual
A-8 For Assistance: Call Toll Free 1-800-476-4849
Grinding Wheel
Cutter Bit
1. Left Side
Clearance
2. Rigt Side
Clearance
3. End
Clearance
4. Radius 5. Top Rake
Oilstone