So I was happily parting away with my 25mm MGEHR 2525-3 parting tool running 92rpm with 90mm stock(about 3.5in), using cross power feed at 1 thou per rev, squirting oil into the groove every few seconds. The whole piece is about an inch long. It's held in a 3 jaw chuck through very thin aluminium shims on 8mm (1/3 of an inch) of its length, then there is a 2mm wide, 3mm high shoulder to prevent the part migrating into the chuck on heavy drilling, about 15mm (0.6in) of slightly smaller diameter (86mm, or 3.4in)is sticking out in front of the shoulder. There is a 48mm (almost 2in) threaded hole through the piece. I'm cutting right in front f the shoulder so 2mm (80 thou) from the chuck.
When about 20mm (2/3rds of an inch) in BOOM and my work piece is jammed stopped, the spindle is stopped and the 3ph motor is buzzing loudly.
I hit the stop switch in under a second. Then I assess the damage. I see the part is kinked in the 3jaw. I loosen it. I move the carriage right with the part now permanently attached to the front of the tool and I rotate the spindle by hand, then repeat in gear... It feels fine... It was very lucky...
Then I try to start the motor and all I hear is a loud buzz, so I stop it straight away and I discover one of three phase fuses has blown. I replace it and the motor works fine. Great.
Then I look at my part. I move it back and forth by hand and eventually I manage to free it. But the bottom-front of the Mgehr2525 insert tool is gone :-(
Also the insert pieces are jammed in the groove in way I can't remove them. So there is no way I'm band sawing this.
Eventually I chucked the part and I faced off what was before the chuck side until I got to within 10 thou of the parting groove. Then I cut from the inside hole out and a 10 thou thick disk of material fell off. It seems I was within few mm of parting all the way when it happened.
Then I removed all the big chunks of the insert. I ground off any gouges that could have had insert pieces in and I faced the part. It was saved.
Now, I have a Mgehr tool with the front half of its bottom jaw missing :-( I can put an insert in, but last quarter of a inch (6mm) is unsupported. Clearly I can't use it like that. Option one is to buy a new tool (they're not that expensive) or try fixing it. I know which option I'll choose. I'll try to build that edge back up by tig welding and filing it to shape. The question now is what filler to use. Mild steel will surely not be strong enough. I'm leaning towards using stainless filler, but I worry it will increase a chance of the tool "grabbing" in future. What do you think?
As for lessons learned... I really have no idea. I've used this parting tool about 4 times before on similar diameter and same material with the same oil lubrication. Perhaps I was a second late in oiling? I didn't think that would matter. The tool was on center (checked with a height gauge) and parallel (set before the cut). The only thing I can think of is that the piece must have slipped in one of the Jaws, it kinked and a side grabbed, then it was a chain reaction.
The morale of the story is, don't part unless you're having full length of 3-jaw jaws holding the part. It doesn't matter how secure the part feels in the chuck.
When about 20mm (2/3rds of an inch) in BOOM and my work piece is jammed stopped, the spindle is stopped and the 3ph motor is buzzing loudly.
I hit the stop switch in under a second. Then I assess the damage. I see the part is kinked in the 3jaw. I loosen it. I move the carriage right with the part now permanently attached to the front of the tool and I rotate the spindle by hand, then repeat in gear... It feels fine... It was very lucky...
Then I try to start the motor and all I hear is a loud buzz, so I stop it straight away and I discover one of three phase fuses has blown. I replace it and the motor works fine. Great.
Then I look at my part. I move it back and forth by hand and eventually I manage to free it. But the bottom-front of the Mgehr2525 insert tool is gone :-(
Also the insert pieces are jammed in the groove in way I can't remove them. So there is no way I'm band sawing this.
Eventually I chucked the part and I faced off what was before the chuck side until I got to within 10 thou of the parting groove. Then I cut from the inside hole out and a 10 thou thick disk of material fell off. It seems I was within few mm of parting all the way when it happened.
Then I removed all the big chunks of the insert. I ground off any gouges that could have had insert pieces in and I faced the part. It was saved.
Now, I have a Mgehr tool with the front half of its bottom jaw missing :-( I can put an insert in, but last quarter of a inch (6mm) is unsupported. Clearly I can't use it like that. Option one is to buy a new tool (they're not that expensive) or try fixing it. I know which option I'll choose. I'll try to build that edge back up by tig welding and filing it to shape. The question now is what filler to use. Mild steel will surely not be strong enough. I'm leaning towards using stainless filler, but I worry it will increase a chance of the tool "grabbing" in future. What do you think?
As for lessons learned... I really have no idea. I've used this parting tool about 4 times before on similar diameter and same material with the same oil lubrication. Perhaps I was a second late in oiling? I didn't think that would matter. The tool was on center (checked with a height gauge) and parallel (set before the cut). The only thing I can think of is that the piece must have slipped in one of the Jaws, it kinked and a side grabbed, then it was a chain reaction.
The morale of the story is, don't part unless you're having full length of 3-jaw jaws holding the part. It doesn't matter how secure the part feels in the chuck.