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Thread: Ridgid tapping on Fanuc

  1. #25
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    Quote Originally Posted by deneyeone View Post
    Have you tried using G32?
    Ex:
    S100xM3
    GO X0 Z.25
    G32 Z-1.0 F(pitch of tap)
    M5
    Z.25M4
    I have always been able to rigid tap using this method on most lathes with Fanuc control.
    I can't imagine how this would work if the tap were held rigidly, rather than in a floating holder. The reason being is the inherent Thread Lead Error experienced due to Acceleration/Deceleration when the Z slide stops and starts at the Z end point of the thread.

    Using G32 in normal thread cutting there is an area at the start and finish of the thread where the Thread Lead will be incorrect due to Acceleration/Deceleration; there is even a description by Fanuc of a formula for calculating the length over which the error will occur at the start and end of the thread. In normal thread cutting with a single point tool, this Lead Error is confined to the start and finish area of the thread, but used in a tapping operation with a rigidly held tap, the the error, due both to the Deceleration and Acceleration at the bottom of the tapped hole, would occur over the full engagement length of the tap.

    You may get away with it using quite slow RPM, as the Lead Error is directly related to lead of the thread and the spindle RMP, but there would still be some error.

    Rigid tapping is an option that's available on the main spindle of a lathe and is not confined to live tooling only.

    With regards to the varying inertia that the system could have to deal with (varying mass of the work holding and work when the main spindle is involved) and varying spindle RPM that may be applied, I can't say how Fanuc deal with this. However, on systems where I've been involved with writing control software, and therefore been privy to the functions of the servo system, its clear that most have a function where the torque being experienced can be queried. That being the case, I can think of a few ways to deal with the varying inertia that may be encountered when rigid tapping with the main spindle. I'd be confident that Fanuc would not have overlooked this fairly obvious matter.

    Regards,

    Bill

    Last edited by angelw; 11-29-2011 at 03:21 AM.


  2. #26
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    "Rigid tapping is an option that's available on the main spindle of a lathe and is not confined to live tooling only."

    Can you please give more information.
    Which cycle to use?
    I was under the impression that even if rigid tapping option is available, G32 cannot rigid tap.



  3. #27
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    Quote Originally Posted by angelw View Post
    I can't imagine how this would work if the tap were held rigidly, rather than in a floating holder. The reason being is the inherent Thread Lead Error experienced due to Acceleration/Deceleration when the Z slide stops and starts at the Z end point of the thread.

    Using G32 in normal thread cutting there is an area at the start and finish of the thread where the Thread Lead will be incorrect due to Acceleration/Deceleration; there is even a description by Fanuc of a formula for calculating the length over which the error will occur at the start and end of the thread. In normal thread cutting with a single point tool, this Lead Error is confined to the start and finish area of the thread, but used in a tapping operation with a rigidly held tap, the the error, due both to the Deceleration and Acceleration at the bottom of the tapped hole, would occur over the full engagement length of the tap.

    You may get away with it using quite slow RPM, as the Lead Error is directly related to lead of the thread and the spindle RMP, but there would still be some error.

    Rigid tapping is an option that's available on the main spindle of a lathe and is not confined to live tooling only.

    With regards to the varying inertia that the system could have to deal with (varying mass of the work holding and work when the main spindle is involved) and varying spindle RPM that may be applied, I can't say how Fanuc deal with this. However, on systems where I've been involved with writing control software, and therefore been privy to the functions of the servo system, its clear that most have a function where the torque being experienced can be queried. That being the case, I can think of a few ways to deal with the varying inertia that may be encountered when rigid tapping with the main spindle. I'd be confident that Fanuc would not have overlooked this fairly obvious matter.

    Regards,

    Bill
    Because if a lathe doesn't have live tooling, there is generally no c axis control, so no reason to monitor accel
    and decel that close. it's not a fanuc issue, it's how and what the builder buys from fanuc and implements it. These are Commodity machines, and they need to keep the price down to be competitive.



  4. #28
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    Quote Originally Posted by underthetire View Post
    Because if a lathe doesn't have live tooling, there is generally no c axis control, so no reason to monitor accel
    and decel that close. it's not a fanuc issue, it's how and what the builder buys from fanuc and implements it. These are Commodity machines, and they need to keep the price down to be competitive.
    Acceleration/Deceleration occurs with everything that changes direction; that's basic physics. Some people have the idea that reciprocating pistons in an engine or pump never stop. But they come to a stone motherless stop twice per revolution of the crank shaft.

    In screw cutting, irrespective of the threading cycle or threading G code used to keep the slide in sync with the spindle, there is Acceleration when the tool start the threading pass, and Deceleration at the end of the thread, when the slide must come to a complete stop to be able to return in the opposite direction to the threading start position.

    Whatever way you want to argue this, Acceleration/Deceleration is chiseled in rock, and its the reason why, theoretically, rigid tapping won't occur correctly with G32. As stated in my last post, you may get away with it to some extent if the spindle speed was kept quite slow and the lead of the thread is relatively fine.

    Sinha:
    The company I provide machine commission services to has just delivered a Femco Lathe with Fanuc Oi Control. This is a new machine, with no "C" axis and no live tooling. I know for sure that this machine has been supplied with the Rigid Tapping option as I was involved with getting the order for the machine and one of the clients requirements was Rigid Tapping, and given the configuration of the machine, obviously with the main spindle. I have not used Rigid Tapping with the main spindle of a lathe, but I'll get all the details when I commission the machine next week and post them here.

    Regards,

    Bill



  5. #29
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    Angelw,
    I may be wrong, but, I believe, there may be a difference between an option being available, and being able to make use of an available option.
    Since G32 is not a cycle, rigid tapping may not be possible with this.
    I am eagerly waiting for what you find out on this machine.



  6. #30
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    Quote Originally Posted by sinha_nsit View Post
    Angelw,
    I may be wrong, but, I believe, there may be a difference between an option being available, and being able to make use of an available option.
    Since G32 is not a cycle, rigid tapping may not be possible with this.
    I am eagerly waiting for what you find out on this machine.
    You're preaching to the Choir Sinha. If you read my post again you will see that I'm saying that you CAN'T correctly use G32 for rigid tapping due to the issues relating to Acceleration/Deceleration and the erroneous thread lead resulting from this. This erroneous lead issue relating to thread cutting is a fact well documented in all Fanuc manuals.

    You have a Forum member saying that they use G32 for the purpose of Rigid Tapping. The only way I can see that happening is if the spindle RPM were quite slow, the lead of the thread reasonably fine, because lead error due to Acceleration/Deceleration is directly related to slide velocity (RPM x Lead of thread), and that the size of the Tap and everything else was going in favor of the operation. I've been called to client's works for what they believed to be machine issues when poor quality threads resulted using G84, only to find they were using Rigidly held taps in a machine that definitely did not have Rigid Tapping. The tap was makings its way in and back out of the hole without breaking, but mashing the thread in the process. If the Lead error was small, because the slide velocity was slow, then you MAY have the operation complete without breaking the tap, but there would be error in the thread over the full contact area of the tap. You would have the actual lead of the tap fighting the erroneous Lead resulting from Deceleration as the slide came to stop at the bottom of the threaded hole, and also resulting form the Acceleration of the slide when backing the tap out of the hole. If the tap did survive, I suspect that the error in the lead would be transferred to the thread by either deforming the form, or over-cutting the thread. Once the slide was up to speed and synchronized with the spindle again when retracting the tap, I suspect that any deformation would be ironed out to some extent by the reversing tap, but overall, a less than optimal thread would result.

    The machine that I'm commissioning next week is equipped with the Rigid Tapping Option, and undoubtedly will use a dedicated cycle to Rigid Tap using the main spindle, because that's the only spindle it has. Using G32 for tapping with it is not on the agenda. It does not have a "C" axis, but I have seen in documentation I've read prior to the machine arriving, that M19 can be commanded to orientate the spindle.

    Regards,

    Bill

    Last edited by angelw; 12-01-2011 at 02:57 PM.


  7. #31
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    Quote Originally Posted by sinha_nsit View Post
    Angelw,

    I am eagerly waiting for what you find out on this machine.
    Hi Sinha,
    Following is what I found with regards to rigid tapping using the main spindle of a turning centre.

    The machine is equipped with:
    1.Fanuc 0i TD control
    2.No live tooling
    3.No C axis, in that it can’t be indexed to any angular position, nor is there any feed mode available with the main spindle.
    4.M19 function to orientate the spindle in a similar way to that of a machining centre
    5.A load meter switchable between Z and Spindle load

    Following is the format for programming rigid tapping

    N1 G0 G21 G40 G80 G97 G99
    G28 U0.0 W0.0
    T0101
    G54 G0 X0.0 Z10.000 M08
    M29 S1000
    G84 Z–30.00 R5.0 F1.5

    The action of the spindle was the same as when rigid tapping is used on a machining centre, that is, the spindle didn’t start until it went to the R plane and stoped when the cycle was completed.

    The client didn’t have tools for the machine to be able to actually perform a tapping operation. However, we ran the cycle with the chuck only and no material, and with a piece of steel bar measuring approximately diameter 200mm X 300mm long. This was done to give a facsimile of reasonable min and max torque on spindle start and change in direction using the same spindle speed in each case. The load meter set to Spindle, showed a lot more effort being applied to the spindle during the start and stop/reverse phase of the cycle with the large workpiece compared to chuck only, but didn’t show maximum load. Time wise, the programs were the same with and without the material.

    I concede that an actual tapping operation was not performed, but with the results I saw on the load meter and general observation of the cycle running in fresh air, I’m convinced that there would not be an issue rigid tapping various revolving masses using the main spindle.

    Regards,

    Bill

    Last edited by angelw; 12-08-2011 at 05:22 AM.


  8. #32
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    I think on my machine, there is an option for ridgid tapping but the factory has set the parramemts (all the parramets that has to do with the ridgid tapping) to Zero..
    so just in case we want it they come tweak few parramerts and off we go...
    so figiring what parramets belong to what and what they mean is messy job...
    might just leave it and use floating holder.
    thanks for help.



  9. #33
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    Quote Originally Posted by angelw View Post
    ...
    N1 G0 G21 G40 G80 G97 G99
    G28 U0.0 W0.0
    T0101
    G54 G0 X0.0 Z10.000 M08
    M29 S1000
    G84 Z30.00 R5.0 F1.5
    ...
    So far I was under the impression that G84 does not work without live tooling. So, this is a new information for me. Thanks.
    Whenever you have time, please machine an actual job.



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