Breaking of hob when cutting high helix angle gears


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Posted by Russell on July 29, 2003 at 12:06:04:

There has been some serious hob breakage when hobbing the following gear: 14 teeth, 2 module, helix angle 53 degrees Left Hand, using the foll. hob: Single start, 2 module, Lead angle 2 degrees Left hand, semi-topping profile. The radial-axial along with conventional hobbing feed direction (top-to-bottom) was used. Hob speed 140 rpm, radial feed 0.25 mm/rev, axial feed 0.32 mm/rev have been used. Material used is EN8 (normalised), hardness is approx. 175 - 185 BHN.
After hobbing 20 pices successfully the hob broke while the radial feed was on (3.5 mm depth was cut). Is it possible that a momentary drop in the counter-balancing pressure of the hobhead could have resulted in failure.


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