My spindle took a dive on a Friday afternoon job

Was about 3 hours into a 6061 aluminum run last Friday when the spindle just started making this awful grinding noise. Pulled the part quick and saw some weird scoring on the cutter shank. Turns out the drawbar tension was off by about 15% and the collet was spinning inside the holder. Had to shut down the whole machine for the weekend and call a service guy Monday morning. Anyone else had a drawbar issue creep up out of nowhere like that?

3 comments

3 Comments

pat_roberts552mo ago

Hate to pile on @stella_scott96, but she's half right. Drawbar tension doesn't just wander off on its own, but it's easy to miss during maintenance if you're rushing or the gauge is acting up. I had a machine two years ago where the Belleville washers started sagging from heat and actually dropped tension over a long run. It showed up as chatter first, then a slight burn on the shank like you described. Did the service guy find anything specific in the drawbar assembly or was it just a retorque?

corah752mo ago

Pat_roberts55 brings up a good point about Belleville washers. I recall reading a service bulletin from a major machine tool manufacturer that warned about exactly that problem with heat cycles causing the washers to lose their spring rate over time. It's not just a simple torque check, the whole assembly needs to be inspected for wear and flatness. Our shop had a similar issue where the chatter would come and go, and it turned out the drawbar retaining nut had actually backed off slightly from vibration. The service tech found it when they did a full drawbar pull test with a calibrated gauge, not just a quick re-torque. So it is possible for drawbar tension to change, but it usually points to a mechanical problem that needs more than just tightening.

stella_scott962mo ago

Creep up out of nowhere" isn't accurate. Drawbar tension doesn't change by itself. You missed checking it during maintenance.