14072
« on: November 14, 2010, 05:48:05 AM »
First thing to say is there is a vast difference between Threading (single point lathe ) and Tapping.
Threading only requires the Z axis to start at the exact same point (distance and angle) for each pass and the axis to move at the defined feed per rev of the true spindle speed. With lathe threading the actual spindle speed is monitored during a pass and the Z axis speed is adjusted accordingly (within reason).
However and here is where the big difference is, the tool exits the material at the end of the pass and the spindle does not have to slow, reverse and accelerate, so the axis does not need to be totally in sync with the spindle at all times.
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Tapping requires the Z axis to move completely in sync with the spindle as it needs to slow and reverse in sync with the spindle at the end of the thread. Because Mach is a buffered system that is almost impossible to achieve unless as mentioned above you have a Step/Dir motor (servo/stepper) on the spindle acting as an axis. If you had that then the axis (spindle now an axis as well as the others) motion would have been planned taking into account the acceleration etc of each axis and would assume that each axis would keep to that, which they should or it means your motor tuning is no use.
Doing tapping whether on a lathe or a mill can be achieved with good results if you use a floating tap holder, this allows for any slight variance in spindle speed and Z axis feed but more importantly allows for float whilst the spindle and axis slow, reverse and accelerate.
One other thing you may want to look at is Thread Milling, this is easy to achieve on a mill as the spindle speed doesnt come into the equation other than for surface speed of the tool. So in thread milling all you need is for X Y and Z to move in sync which Mach can easily do.
What you mention last is using a mill to thread like a lathe and that is possible and as easy to do as it is on a lathe but I am not sure if G76 threading cycle will work on a mill profile, you may have to open a lathe profile to achieve it.
Hood