hold on

[snascar2424]

I'am having a problem getting inconel 718 to quite either slipping and pushing back. I have the hydraulic preasure maxed still will push back. I ran this job a month ago same material no problem. I just bought a 16c serrated collet helped a little but still pushes back. I was pushing 100 sfm @ .011 ipr no problem. I have dropped feed rate to .007 ipr I should be having no problem at this feed rate for sure. I have tried taking lighter cuts but this kills the cycle time. my turn to drive ratio is 2.33. any ideas?

[flick]

Insert grade/geometry?

Is the chuck greased regularly? Could it be exerting less radial force for the same hydraulic pressure due to lack of maintenance?

Are you running off the bar, or would it be possible to use stepped soft jaws?

EDIT: just saw the note about turn to drive ratio. use accurately bored stepped soft jaws and get a shoulder/face positively located.

EDIT2: but check to see that you're getting good grip first. This job shouldn't be slipping assuming a reasonable DOC. (0.1ish on a middle weight lathe - what kind of machine?)

[snascar2424]

the chuck is brand new less than one month's use. we are running from bar no slugs however we could slug these parts but its hard on band saw blades.

[g-codeguy]

I can't tell you why it ran fine last time, but pushes back this time. Like another poster, I will also ask "What machine?" I can tell you from personal experience that our Daewoo Lynxes using 16C collets versus the Hardinge lathes using the same collets, can't handle the same DOCs without pushing back. Can't answer why either unless it is because the Daewoos use an adapter to mount the collet while the Hardinges don't.

One thing I like to do with this type of material is to use ground inserts for roughing because they cut freer. Preferably a positive rake one like CNGP. Even better is to use positive rake tools such as a cpmt holder instead of a negative rake tool like the cnmg holder. A ground insert isn't normally a good choice for roughing and tool life will suffer, but sometimes compromises have to be made.

[snascar2424]

I talked with the machine dealer and the pump in set to max out hydraulic preasure at 4.5 mpa I can set this number high maybe 5-6 mpa which is still under 1000 psi. The guage on the machine is well in to the red zone but according to hardinge the collet will take approx 7000# worth of preasure. this machine is big enough you would think no big deal the only thing that worries me is sending the chuck preasure that far into the red zone on this machine . red zone starts at 3.5 mpa and goes to 7 mpa.

[Jawbreaker38]

Just a thought, what about trying an insert with sharper nose radius? If for example you're using a .031 radius insert try going to a .015 radius instead. Seems to me that this may reduce tool pressure. I don't have much experience turning, and I'm not sure if it would help or not.

[Delw]

sounds to me like you could have slipped off center. those feeds and speeds are pretty good a tad high but they will just junk inserts faster.
I have cut 718 in a omni turn with ccmt inserts and a 5c air collet and get no push pack or stalled axis usually about .025 per cut.


one other thing too look at is make sure your not close to the bototm of the stroke on you chuck movement, if you removed the collet to spindle nut for any reason make sure its put on all the way.

oh yeah check to see if the collet pin is rubbing or gouged that will keep the collect from moving freely and possible binding.