D1-4 Cam Stud Break

[Roger Taylor]

After cutting the cooling fins on my Crusader 60 cylinder, I used the same hand ground HSS bit for the part-off. About halfway through the hand feed operation, the bit caught ever so slightly, and the chuck studs sheared off dropping the chuck onto the bed as in the attached photo. eighty-five RPM, flood coolant, with the cut as close to the chuck as possible and the carriage locked, I've done this operation hundreds of times. The Harrison M300 13" lathe was Navy surplus and came with a 9" Buck 3-jaw. plus, a large 3-J Hardinge hand wheel collet setup. I have used that chuck for twenty-five years never suspecting that the oversize could put a destructive strain on those cam studs or maybe the heat tread was not correct. Fortunately, at low RPM the only damage was to the studs. Anyway, just a heads up for folks to check stud adjustment and possibly a die penetrant check if any issue is suspect. I have replaced the studs and also invested in a 6" 3-jaw for 80% of my work.

 

[Jeffro]

By the look of these photos, I suspect the poor contact of the taper area has transferred load to the hold studs.

 

[Roger Taylor]

By the look of these photos, I suspect the poor contact of the taper area has transferred load to the hold studs.

Thanks, i did do a thorough measurement of the matching tapers major, minor diameters and length. The .437" L taper fits up tight but that small taper length seems to be more for accurate registration than holding power. I was pleasantly pleased and surprised that the 6" Shars chuck mount snugged up to the lathe spindle with no discernable slop.

 

[rklopp]

Were the chuck and spindle flat faces mated tightly? They should have been, or else all the cyclic fatigue load was directed at the studs. The situation is a lot like auto wheel lugnuts. They need to be tight to minimize the cyclic loading component. Steady high stress is preferred. That said, the studs in your case look like they failed in brittle fashion. That may suggest hydrogen embrittlement or a bum heat-treatment.