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Chipping The cutting edge is broken off instead of being worn away. Caused by:
• Excessive feed rate
• Interrupted cut
• Insert geometry too weak
• Chatter
Cratering Characterized by a smooth depression on the face of the insert. Caused by:
• Excessive cutting speed
• Ineffective use of coolant
• Friction
• Normal wear
Oxidation
• Occurs during very high cutting temperatures
• Weakens tool tips
Chemical wear: Cutter/workpiece reaction begins to corrode insert (corrosion)
Coolant
There are a number of reasons why coolant is used in the machining process; it is used
to dissipate heat generated during machining, reduces cutter friction, and promotes chip
clearance. It also allows for high speed machining and increases tool life.
Coolant is not recommended when machining cast iron or steel, or when using carbide
cutters. Carbide cutters can withstand high temperatures but not thermal shock of coolant.
Cutting fl uids are best suited for soft materials such as aluminum alloys and brass.
A good fl ow of cutting fl uid should be directed to both sides of cutter whenever possible.
These are the most common types of cutting fl uids:
Emulsion (water combined with mineral oils and additives)
• Used for light to moderate machining
Cutting oils (grease or solid additives)
• Limited to slow speed and low feed conditions due to fl ammability
• Expensive to use
Chemical or semi-chemical fl uids (synthetic)
• Contain no petroleum oils
• Used for more diffi cult machining/grinding operations
Workpiece
The more you know about the workpiece, the better you can control the machining
process. As a general rule ask these questions:
• What is the type of metal (alloy or steel)
• Has the part undergone any special process, i.e. case hardening, treated with
additives or heat treated, etc.?
Feed Rate
Feed rate is determined by the required surface fi nish and cutting force. Expressed in:
• Inches or millimeters per minute
• Inches or millimeters per revolution
• Inches per tooth
Minimum chip thickness (chip load) is determined by the cutting force.
Maximum chip thickness (chip load) is determined by machine power and tool design.
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96-0041 Rev T
January 2009
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