duet for 4+ axis lathe

oliof

@yoshimitsuspeed why would RRF not be suitable for this?

dc42

@yoshimitsuspeed said in duet for 4+ axis lathe:

and overcome the mentioned shortcomings of RRF?

What are the "mentioned shortcomings" that would be a problem for you?

yoshimitsuspeed

It's my understanding that RRF doesn't do constant state or infinite rotation type operations, or something related to the spindle . As I remember from what I have read that seems to be the big hangup but I feel like I read of other things that sounded less than ideal as well.

Also to clarify, this would be using a stepper or servo motor on the spindle with a toothed belt or similar so spindle angle is fixed to the motor to be able to do threading and operations like that, and hopefully eventually fifth axis machining. So it wouldn't just be "set spindle voltage or PWM to approximate RPM" but would be operations that precisely tie the spindle moves to other axis moves.
Of course now I am trying to find the threads or places I found this being discussed and can't find it.

Ah here is one. So I guess the issue is less regarding defined rotation operations but theoretically infinite or continuous rotation operations.

T3P3Tony

@yoshimitsuspeed one thing I am aware of as a wished for feature is synchronization of rotary "circumference velocity" (apologies I don't know the correct CNC term) with other linear axes velocity. Ie. The feedrate is constant no matter the radius from the axis of rotation, rather than being a constant angular velocity.Is that what you are referring to?

Synchronisation between the rotary axis and the linear axes is already possible. I have done a bunch of test prints printing on a printed mandrel. I first print the mandrel by rotating C with an X offset, then rotate B so the mandrel is now in a traditional horizontal orientation then print a spiral on that using synchronous C and X axis axis moves. That's the additive equivalent of thread cutting (thread printing?). I used meta gcode to scale the extrusion amount and feedrate based on the distance from the center of C axis rotation (the Z offset). This kept the extrusion and feedrate constant as the printed spiral grows in offset from the center of rotation.

dc42

@yoshimitsuspeed RRF can do finite axis rotations synchronised to other axes, however you are limited to 2^31 motor microsteps in each direction before resetting the position (e.g. using G92).

yoshimitsuspeed

@T3P3Tony
Yes you are talking about constant surface speed and that would be critical to a properly functioning turning setup. But it's not what I was talking about.
I guess what I was reading about must be what @dc42 is talking about.

o_lampe

@yoshimitsuspeed Yes, for threading you could turn the spindle into a sync'd axis and with 2^31 microsteps you could run it for days before reaching the fence

I've done some CNC milling with Duet boards in the past and it was already nerve wracking sometimes. Using it for a lathe would be even less convenient IMHO.
I wouldn't want to do that on daily bases or for earning money.

yoshimitsuspeed

@o_lampe

Thanks for the input.

There wouldn't be any easy way to use a Duet board controlled by LinuxCNC or something like that would there?

T3P3Tony

@o_lampe said in duet for 4+ axis lathe:

already nerve wracking sometimes

Why? We are seeing a growing number of users using it for 3 axis milling for example.

T3P3Tony

@yoshimitsuspeed I have heard people talking about using Remora with Linux CNC but AFAIK they support STM32 but not the SAM based processors on the Duet board.

I have opened a feature request for this:
https://github.com/Duet3D/RepRapFirmware/issues/985

The other important feature that I am aware of is true Feed Hold, there is already an outstanding feature request for that:
https://github.com/Duet3D/RepRapFirmware/issues/745

T3P3 created this issue in Duet3D/RepRapFirmware

open Implement constant surface speed mode for lathes/rotary machines #985

T3P3 created this issue in Duet3D/RepRapFirmware

open Feed hold #745

o_lampe

@T3P3Tony I never felt at ease when navigating through various coordinate systems.
Changing a mill bit and setting new z-zero meant pure adrenalin and full concentration for me.
I had to switch through machine/workspace coordinate systems back and forth and without the conditional macros it was all done manually.

Nowadays it's just a matter of writing a bulletproof macro, but I already wrecked my Y-axis because one motor got stuck while the other went on.
IDK if there is a cross check method for stall detection now? (one y-motor stalls and both stop automatically)
When I tried to set it up, I only got popup messages in DWC and had to react accordingly. Fingernail biting time....