MPCNC 4th rotary axis

Jodougie · January 14, 2022, 7:26am

I’m currently adding a 4th rotary axis to my MPCNC.
I’m going to use GRBL MEGA 5X with TB6600 drivers to control everything.
GRBL GRU seems to be an obvious choice for controlling the drivers.
Has anyone done similar?
Has anyone got and advice to offer

vicious1 · January 14, 2022, 4:09pm

A few around here have done it, but how are you going to make the CAM?

Jodougie · January 14, 2022, 5:06pm

I’ve thought to use DeskProto Multi Axis Edition.
I’m learning this CNC stuff as I go along. I have degrees in engineering but didn’t work much with CNC in my career… I make mistakes and blow control boards up
What do you think…
I’ve also made a lowrider. I’m using GRBL on a CNC shield on that… Its brilliant. Thank you for your help and designs

Tokoloshe · January 15, 2022, 8:42am

Maybe this might help you: ZenziWerken | PoorMans4thAxis

Jodougie · January 22, 2022, 10:40am

Hello. Just an update on my project…
The firmware is working now. GRBL MEGA 5X controlled by GRBLGRU.
I’ve mounted the MPCNC on a open box section frame. This allows me to place it atop some big timber slabs. Making it very portable.
It also allows me to sit it above the 4th rotary axis assembly. That works really well too. I can now rotary carve at will.
I can post a video of it working somewhere if anyone’s interested

robertbu · January 22, 2022, 3:15pm

I’m interesting some video and/or pictures.

vicious1 · January 22, 2022, 4:48pm

Yes please!

Mattk331 · February 21, 2022, 12:38pm

Did you ever get a chance to post pictures and videos of this? I’m interested in seeing what you came up with.

Jodougie · February 21, 2022, 8:02pm

Hello. Yes i will post some pictures tomorrow. Im really please with this. Its tight and accurate. Ive made a probe to height map uneven surfaces. With the help of Gaithier Briere on the grbl Mega5x forum i managed to get a laser firing properly.
So i can now 3d rotary carve and burn.
The software to control the board is GRBL GRU. It has presets for both MPCNC and Lowriders.
So far its all good. Ill get some photos up tomorrow

Jodougie · February 22, 2022, 10:52am

Jodougie · February 22, 2022, 10:54am

Still needs tidying up but it all works superbly

Mattk331 · February 23, 2022, 1:09am

Ok! Now you have to show it working! Very cool.

Mattk331 · February 25, 2022, 11:37pm

Hmmm, i have an uno and cnc shield laying around… might have to see if i can make it work. Would love a rotary axis to make chess pieces. Might have to pick your brain some…

Jodougie · February 26, 2022, 7:07am

Hi. The UNO will run GRBL 1.1
GRBL 1.2 is needed for true 4 axis work on an Arduino Mega… However… its easy enough to use the X or Y axis to drive the 4th axis.
Great tutorials on 3d carving using 3 and 4 axis CNCs can be seen on the DeskProto U tube channel

RockinRiley · September 9, 2022, 12:47pm

So when you did this. Is there a how to on getting all the axis set up and calibrated?
I really want to do this.

robertbu · September 10, 2022, 11:59am

Yesterday, Jamie mentioned there is now native support for a rotary axis. Not sure what is involved in getting it working, and you will likely need to “upgrade” your Marlin to a nightly build.

jamiek · September 10, 2022, 6:57pm

This is what I saw in the config:

github.com

MarlinFirmware/Configurations/blob/1153f674311a1f28b2e10c6b9cde5a31ae70cdfa/config/default/Configuration.h#L200

      
        
            * AXISn_NAME defines the letter used to refer to the axis in (most) G-code commands.
            * By convention the names and roles are typically:
            *   'A' : Rotational axis parallel to X
            *   'B' : Rotational axis parallel to Y
            *   'C' : Rotational axis parallel to Z
            *   'U' : Secondary linear axis parallel to X
            *   'V' : Secondary linear axis parallel to Y
            *   'W' : Secondary linear axis parallel to Z
            *
            * Regardless of these settings the axes are internally named I, J, K, U, V, W.
            */
            #ifdef I_DRIVER_TYPE
             #define AXIS4_NAME 'A' // :['A', 'B', 'C', 'U', 'V', 'W']
             #define AXIS4_ROTATES
            #endif
            #ifdef J_DRIVER_TYPE
             #define AXIS5_NAME 'B' // :['B', 'C', 'U', 'V', 'W']
             #define AXIS5_ROTATES
            #endif
            #ifdef K_DRIVER_TYPE
             #define AXIS6_NAME 'C' // :['C', 'U', 'V', 'W']

So I guess this would make it up to 9 (non-extruder) axes.

I’m not sure why the ‘rotates’ flag matters. If it’s just another axis and you assign the gear ratio in terms of steps-per-unit and velocity in units-per-second, when does it matter if units are degrees or mm? I highly doubt that Marlin is attempting to interpolate straight lines on a SCARA robot for example.