From time to time on this forum a few threads have touched on the idea of controlling lathe speed to maintain a specified surface speed.
This thread will be a stub to pool ideas and perhaps develop a group designed project to make this possible.
The sytarting point is a variable speed spindle drive with external control.
VFDs running a 3-phase motor is one of the options. Others may be DC dries with PMW electronic control or even setro drives with amplifier control.
So far, the discussions have proposed to fit a multi-turn potentiometyer to the cross-feed screw and a linerar slide potentiometer moed by the cross slide mechanically.
Both options would provide a linear variation in resistance or - if used as a voltage divider - variable voltage in response to tool position in relation to the cutting radius.
I was quickly identified that this is not a direct relationship to desired spindle rpm, since other ariables are material cut, tool geometry, machine rigidity, turning operation (turning versus facing), and desired speed range for specific purposes like threading for example.
My last comment in another thread was to suggest using the positional data of a potentiometer as just one of the inputs to a 'black box' processor with additional operator inputs for measured starting radius, desired surface speed (maybe this could include a reference to material machined), allowances for tool geometry and chatter avoidance. In addition, the set motor to spindle drie ratio will need to be able to be set.
These variables would then be used to feed the actual motor controller - such as a VFD - with the signal required to set the spindle speed and vary it to maintain a desired surface speed as the turing operation changes the cutting radius.
I imagine CNC machines hae all these parameters already worked out and some input from our experienced CNC operators and designers/builders will be greatly appreciated.
This thread will be a stub to pool ideas and perhaps develop a group designed project to make this possible.
The sytarting point is a variable speed spindle drive with external control.
VFDs running a 3-phase motor is one of the options. Others may be DC dries with PMW electronic control or even setro drives with amplifier control.
So far, the discussions have proposed to fit a multi-turn potentiometyer to the cross-feed screw and a linerar slide potentiometer moed by the cross slide mechanically.
Both options would provide a linear variation in resistance or - if used as a voltage divider - variable voltage in response to tool position in relation to the cutting radius.
I was quickly identified that this is not a direct relationship to desired spindle rpm, since other ariables are material cut, tool geometry, machine rigidity, turning operation (turning versus facing), and desired speed range for specific purposes like threading for example.
My last comment in another thread was to suggest using the positional data of a potentiometer as just one of the inputs to a 'black box' processor with additional operator inputs for measured starting radius, desired surface speed (maybe this could include a reference to material machined), allowances for tool geometry and chatter avoidance. In addition, the set motor to spindle drie ratio will need to be able to be set.
These variables would then be used to feed the actual motor controller - such as a VFD - with the signal required to set the spindle speed and vary it to maintain a desired surface speed as the turing operation changes the cutting radius.
I imagine CNC machines hae all these parameters already worked out and some input from our experienced CNC operators and designers/builders will be greatly appreciated.
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