Chip thickness is one of the more important factors affecting tool life in peripheral milling operations. Very thin, or feather-edge chips dull cutting edges more rapidly than thick ones. Chip thickness is governed by the size and relative location of cutter and work piece. It is also affected by the feed per tooth.

GENERAL RECOMMENDATION AND CORRECTIVE MEASURES

Following are some of the more common situations encountered and corrective measures involving variation in speeds and feeds which may be taken to offset them.

Chipping of the cutting edge -

Reduce feed per tooth

Burning of the cutting edge -

Reduce speed

Chatter -

Vary speed and feeds

 

SHARPEN AT PREDETERMINED WEAR LAND

Cutters should be sharpened as soon as the wear land reaches a predetermined width. This width should permit sharpening without excessive loss of tool life. It may vary from a few thousands to 1/16", depending in the type of cutter and the finish required on the product.

SHARPEN AFTER PREDETERMINED PERIOD OF USE

A "time period" to determine when to sharpen a cutter is often used or product runs where all conditions are repetitively uniform. The time period is the length of time it takes a sharp cutter to develop a width wear land indicating that it should be sharpened.

A sharpening program based on a period of use generally requires good uniform machine and product conditions.

SHARPEN WHEN PRODUCT QUALITY INDICATES

Sharpen cutters when product finish is unsatisfactory, or when product size is not within dimensional tolerances. As a cuter dulls in use, it cuts less freely than when sharp and has a tendency to produce rough finish and size.

End mills are usually reconditioned by sharpening the relief and clearance surfaces of the peripheral teeth. Occasionally, however, there is a requirement of minimum diameter loss and it then may become economical to resharpen end mills by grinding the flute face and fillet to remove the wear land and restore the original flute shape. Re-cutting or "gumming out" of flutes can generate a great deal of heat and may damage the tool material.

When usage demonstrates that a cutter works well on a particular application, it should be resharpened with the same relief angles.