Saturday, May 26, 2012

Regrind Endmills?

Should you regrind/resharpen your carbide endmills? Here's a section from the Dormer Regrinding Guide with our comments in red italics:


RESULTS OF REGRINDING

Reduction in Diameter 
A loss in diameter occurs when grinding the periphery of the primary land. This 
progressively impacts the end mill’s deflection capacity when under load. Compare 
Figs. 1 and 2.
The change in diameter changes the tool point frequency much like different diameter tubes of a wind chime produces different tones.

Reduction In Radial Rake Angle
An end mill must possess a rake angle that is suitable for the material being machined.
After each regrind there is not only a reduction in diameter, but also a subsequent
reduction in the radial rake angle. This, together with the corresponding, if slight change,
in helix angle significantly affects the efficiency of the end mill. Compare Figs. 1 and 2.
Face rake angles can be re-established by regrinding the flute face of the end mill.
Reducing the rake angle increases the cutting forces and the amplitude of the deflection of the tool point, changing its frequency.

Increase In Secondary Land Width
The secondary land width increases substantially as a result of regrinding, which in turn
increases regrinding time and cost. Compare Figs. 1 and 2.

Reduction In Flute Depth
As a consequence of reducing diameter, there is a corresponding reduction in the flute
depth. Because of the subsequent impact on chip evacuation capabilities it can force
the utilisation of feed rates that would be considered far less efficient. Compare Figs. 1
and 2.

Saturday, May 5, 2012

Cutting Tool Cost Comparison Utility

When the Boeing Research and Technology group of St. Louis works with Boeing suppliers to refine their machining processes, the researchers advise these shops to consider more than just the purchase price of the tool. A cheap tool can be expensive, if it limits the productivity of the machine...read more
For your convenience, you can download Boeing's Powerpoint slide and Excel file here.