please, help me with general pinch turning questions

hello :)

let's suppose that 2 tools begin an od pinch turning at same x and :
... same z, thus the cutting edges are mirrored:
...... after final z is reached, should there be enough to dwell the spindle for half a revolution in order to achieve a clean face ?
...... did each tool removed the same quantity of chips ?
... different z, thus both cut the same diameter, but one is a bit behind on z; what is the maximum z difference allowed, after which pinch turning no longer occurs ( only leading tool will cut, while the following will cut air ) ? is it g95 feed / 2 ?

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what is the best approach for difference in relative position between each other tool, like one should be higher on x, and in front on z ? is there a recomandation to have the upper turret tool on higher x, or the lower turret tool on higher x, or it doesn't matter ? should the tools differ on both x&z, or only x, only z, or no difference ( like a mirror cut ) ?

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if a difference in x is used, then should it be like each tool to cut the same doc ? or is there a recomandation for 40-60% for some reason ?

if a difference in z is used, then what should it be, and why ? is it true that, if a z difference exists, then the end face won't look smooth, because each tool finished at different z values ? or, even if a z difference exists between tools, is possible to reach same z end for both tools ? or generic z difference is small, making the aspect of the end face to be accepted ?

please, are there some general guidelines ? like practical approaches, ideas based on which the code approach is built ( beside the need for syncronized labels between turrets ) / kindly :)

so many academic questions.
Upper turret should take most of the job, because the chips and heat are removed more efficient, than on the lower turret. I think, it is mentioned in the manual.
"half a revolution" doesn't make sense, unless the tools are active. Theoretically, yes - should be enough.

hy mr bunny :) i had some doubts, but after seing a few youtube videos, i got it fixed

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Upper turret should take most of the job, because the chips and heat are removed more efficient, than on the lower turret

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if both turrets are identical, is that because is considered that the upper tool has the insert face towards y-, or is there also something else to consider ?

i heared that on a multus with lower turret, one should definetly go harder with the turret, since the upper pivot turret is a bit fragile, or at least not as rigid as the lower turret when it comes to roughing / kindly :)

if both turrets identical, then yes - only heat removal is important. They never are identical. The upper is more rigid - traditionally, if no balance unit, the weight of the upper turret does the work also. The design of the lathe, turret arrangement allows the upper turret to be just bigger. Speaking about Multus and MacTurn - yes. The lower turret is the real turret. The upper is universal multi function "all-in-one" - means less rigid.

When synchronized the turrets will feed at EXACTLY the same Z position if started at the same Z so they are at a 1/2 rev difference when encountering a shoulder. That is what makes the balanced load possible. They can be used however you like. Balanced, different Z chasing , different X chasing - your choice - all is possible.

This is also why during a LAP cycle each block should have a P code in order to keep them in sync when pinch turning.

Heavy interrupted turning is generally avoided on the upper Multus multifunction turret since realignment if crashed is time consuming and the turret is more fragile like algirdas says.

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the upper is more rigid - traditionally, if no balance unit, the weight of the upper turret does the work also

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hy mr bunny :) yup, good point; it means that there is more turning capability for the upper turret, while the lower one will have to always compensate it's mass

please, what is a balance unit ? are there such okuma machines ? i guess that it's used for heavier turrets, etc, like an ascensor counterweight

lt twin star lathes have identical turrets

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Balanced, different Z chasing , different X chasing - your choice - all is possible

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hy mr wizard :) i recently saw a few examples of simultaneous machining, covering not only simetrical turning, but also milling and asimetrical toolpaths

i guess that balanced turning is best for machining without a tailstock, or at least alows machining a part with bigger L/D, that would be impossible to handle with a single turret

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This is also why during a LAP cycle each block should have a P code in order to keep them in sync when pinch turning

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yes, such syncronizing is needed, and especially the 1st pair is critical

considering that rapids are identical, i wonder if it would be possible to pinch turn only with a single pair of P codes ? considering the rigidity of the machine, i don't think that it will have such a big error at the end, in order to justify P codes for each block / kindly :)

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like an ascenstor counterweight

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exactly: there was just a weight balance installed on older lathes. Pneumatic compensation is a modern solution. It's for heavy upper turrets - big machines only.
Sure, Okuma is using that.

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Originally Posted by OkumaWiz

When synchronized the turrets will feed at EXACTLY the same Z position if started at the same Z so they are at a 1/2 rev difference when encountering a shoulder. That is what makes the balanced load possible. They can be used however you like. Balanced, different Z chasing , different X chasing - your choice - all is possible.

This is also why during a LAP cycle each block should have a P code in order to keep them in sync when pinch turning.

Heavy interrupted turning is generally avoided on the upper Multus multifunction turret since realignment if crashed is time consuming and the turret is more fragile like algirdas says.

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i sincerely apologize for bringging this thread back to life, but i suppose it proves i used the search function lol! Wiz, would it be possible for you to send me a program example of what you are talking about here? i would like to get into some pinch turning and it sounds like this method may help a lot to sort out some timing issues i am having. thanks!