Closed loop CNC Servo spindle?
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I am looking into replacing the original motor+controller in my Duet 6HC based Paulimot Lathe CNC conversion with an AC-Servo like this one. A servo spindle would close the loop, and open the doors for CNC thread cutting/tapping and using constant surface speeds.
I am using a modified grbl post processor for my cnc Lathe. It already supports constant surface speeds. But the Duet does not seem to support it.
I did not find any information about using Servo spindles or spindle feedback with the Duet. Is this already possible, or rather a case for the Firmware Wishlist?
Cheers
Max -
undefined MaxGyver marked this topic as a question
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@MaxGyver theres currently no spindle speed feedback so its all open loop at the moment. It would have to go on the wishlist
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@MaxGyver There are lots of people with Taig mills/lathes that use AC Servos for the spindles but not with speed feedback into the controller. And they do plenty of screw tapping.
The output from your servo is the encoder output - which is a lot of data to deal with for a simple controller. Even in LinuxCnc (which I'd bet is the fastest inexpensive CNC control) the discussion of closed loop servos talks about addon hardware to deal with the fast encoder feedback.
So, you might just try tapping without the feedback and see how it works out. A 1KW servo has a LOT of power and wouldn't bog down when tapping.
As for variable surface speeds, I'm not sure how the Duet would not support that. It certainly supports spindles with a speed option using M3.
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@markz said in Closed loop CNC Servo spindle?:
As for variable surface speeds, I'm not sure how the Duet would not support that. It certainly supports spindles with a speed option using M3.
If I recall correctly the Gcode with constant surface speeds does not have a RPM value, but rather the desired surface speed and the controller calculates the rpm value depending on the position of the tool. I will try to post a Gcode example tomorrow.
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@MaxGyver I'm not a lathe user so I looked up constant surface speed online. I see what this does - the spindle RPM depends on the distance of the cutter from the center such that the surface speed stays constant at each distance.
You're right that Duet3d RRF does not support that. It wouldn't be that tough to implement but I'd bet it's not on their current plan since it's very lathe aware.
