Smithy Midas 1220 LTD - Manual (Page 36)

Chapter 8
Grinding Cutter Bits for Lathe Tools
High Speed Steel Cutters
The advantage of HSS cutter bits is you can shape them to exact specifications through
grinding. This lets you grind a stock shape into any form. Stock shapes come in an
assortment of types, including squares, flats, and bevels. Many shops buy their cutters as
ready-ground or ready-to-grind bits or blades.
Ready-to-grind bits and blades are of specially selected HSS, cut to length and properly
heat-treated. They are fine tools in the rough and generally superior to HSS shapes sold
by the pound.
In grinding HSS cutter bits, you have five major goals:
• A strong, keen cutting edge or point
• The proper cutting form (the correct or most convenient shape for a specific
operation)
• Front clearance away from the toolpoint
• Clearance away from the side of the tool (side rake)
• Free chip movement over the tool and away from the cutting edge.
Keenness angles can vary from 60° for mild softness to 90° for hard steels and castings
(Figure 8.1).
Figure 8.1 Keenness angles vary from 60 to 80 degrees.
Side Clearance
3-10o
Angle of
Keenness
Side
Rake
8-1
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