4th Axis as Y2 Z or A?

Machine: Homebrew

Board: Cohesion3D Laser Board with external Steppers

Firmware: Thinking of using GRBL-LPC


I am building a laser where I will need two Y motors. I have the Cohesion3D Laser board. When I set the jumper to make the 4th axis follow Y will that prevent me from using a rotary? I don’t know if Z can be used for the rotary or not? From what I have read it does not look like I will be able to use Z as a Y2. I am not interested in using a Z-Table just a rotary with this setup. Any suggestions or advice?

Thank you.

You can change the pin assignments in the config file for smoothie pretty easily to swap Z and A outputs, but you’d have to recompile grbl-lpc for the same thing.

Any suggestions on guides and instructions for doing this? I do not have much experience in these areas. I am willing to learn but need more direction and a solid starting point.

I wrote answer, below, but I need to clarify first - are you looking to use the onboard drivers on the LaserBoard, or are you asking about how to do this for external drivers? The answers will differ greatly.

Here is the response I wrote for how to use flip the the onboard drivers. However, this is very different when you use the external driver breakout ports.

On the included Smoothie firmware, you would edit the config.txt file on the board’s memory card using the Sublime Text editor on your computer.

Starting around line 48, take the step, dir and en pins form beta, and switch them with gamma. Save, safely eject, put the card back into your board while off, then power it up.

beta_step_pin 2.1 # Pin for beta stepper step signal
beta_dir_pin 0.11 # Pin for beta stepper direction
beta_en_pin 0.10 # Pin for beta enable
beta_current 0.6 # Y stepper motor current
beta_max_rate 24000.0 # mm/min
beta_acceleration 2500 # mm/sec²

gamma_step_pin 2.2 # Pin for gamma stepper step signal
gamma_dir_pin 0.20! # Pin for gamma stepper direction
gamma_en_pin 0.19 # Pin for gamma enable
gamma_current 0.6 # Z stepper motor current
gamma_max_rate 24000.0 # mm/min
gamma_acceleration 2500 # mm/sec²

The ! after the dir pin flips the direction - I recommend individually testing your dual Y axes to make sure they each move in the correct direction, and adding/ removing the ! on each

The currents for the onboard motors do not change, however, the first driver will always be mapped to alpha_current and the fourth will always be delta_current

Thank you. I should have said I would be using external steppers for this project. The information will be helpful for the other smaller laser I have that has 2 Y motors. I plan on getting a LaserBoard for it in the near future.

The one I will be working on first has the external steppers. Both motors will have to be going the same direction. The laser is loosely based off of the OpenBuilds WorkBee where the motors will be in back with a lead screw drive setup.

The other one is a cheap Chinese laser diode machine that has been converted to use a set up similar to the X-carve original and the Y motors with it have to be set to go opposite directions. I had an old Arduino board running it, but my kid needed it for a school project and I’ll never see that thing again…

Thanks for the time to help with this.

1 Like

The select 4th driver Y vs A is strictly for the soldered onboard drivers.

For the external driver expansion ports on LaserBoard, they are always signals for X, Y, Z, A and not affected by the Y vs A jumpers.

I looked at the Workbee (I have a 2’ x 4’ scaled up Routy-OX hybrid myself) - the openbuilds Nema 23’s are 2.8 amps so it would make sense to use 2 separate external drivers for dual Y if you want to run these at full power.

You should use our external driver cable to run to the first driver, and use simple hookup wire to run the same set of 6 signals over to the 2nd external driver.

This is a fairly unique case so far, but I could be persuaded to design and make a splitter board so that you can wire 2 drivers as easily as the one with the cable directly from LaserBoard.


Thank you for the info.
I have a bunch of these PCB boards:

Could I do something like this (please excuse my drawings I have MS and legally blind so can’t draw straight):

This way the signal from the LaserBoard is sent to one place and then split to the stepper drivers?

Yes that would work.

Awesome. Thank you all.