Resharpening: Protecting Your Investment

Broach tools represent a significant capital investment, and proper resharpening is essential to getting the most out of that investment. Knowing when to resharpen—and doing it correctly—can mean the difference between consistent, high-quality parts and costly scrap.

Signs that resharpening is needed include a visible whitish wear land on the cutting edges, abnormal wear or chipping, chips packing into the gullets, undersized parts (the go-gauge no longer passes), degraded surface finish, excessive heat at the end of the stroke, or abnormally high cutting forces on the broaching machine.

Best practices for resharpening start with preparation. Remove any material adhered to the cutting faces, check and correct any warpage in the tool, and mount the broach securely in the sharpening machine. Use a sharp CBN grinding wheel—as large a diameter as practical—and dress it regularly. Grind the same amount from each tooth to uniformly remove the worn zone. For internal broaches, pay careful attention to the grinding wheel angle relative to the broach to avoid interference between the wheel and adjacent teeth. The correct wheel angle depends on the relationship between the broach diameter, the wheel diameter, and the cutting edge rake angle.

After resharpening, verify that all wear and chipping have been completely removed, that there are no grinding burns, that the resharpened surface finish is Ra 3.2 µm or better, that the tool has been degaussed, and that the gullet surfaces are smooth and free of irregularities that could impede chip flow.