I am looking to see what the easiest way to add a rotary axis to a MPCNC. I have read a few post about this and it seems best way to go is to use Mach 3 and a USB control board with a PC? I am wanting to make long tapered pool cues and also to use it to carve out negative space for inlays. I have a mostly completed MPCNC with marlin control board already and I was wanting to switch it to be able to use a 4th axis to be able to cnc on round objects. I would not need the Y axis so would it be possible to use a marlin board and substitute the Y axis for the rotary A axis or would this still need to be ran with Mach3? Any advise on what would be the best/easiest conversion for 4th axis or rotary axis stepper assembly?
thank you,
I always link this instruction: ZenziWerken | PoorMans4thAxis I don’t know if it helps, but might be a start. 
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You beat me to it!
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I haven’t used it a whole lot, but the rotary attachment for my K40 laser replaces the Y stepper. For background, I’m using a CNC Shield/Arduno Uno controller, grbl firmware, and Lightburn.
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@redeye_joe or anyone else interested, I have this set up, (ZenziWerken | PoorMans4thAxis) but have since purchased a laser with a rotary and will use it. I am willing to pass on what I have, no stepper motor but everything else is ready to go. Cover the shipping and it’s yours.
If you’re ditching Y, that’s 1 to 2 spare axis right? You likely would just need to flash with the proper configs and wire it up to match.
The reason folks upgrade boards when adding rotary is usually to keep xyz and dual endstops, which does require a 6axis control. Also, in this case it doesn’t have to be mach3 unless you want… most 6axis grbl or marlin controllers would also work.
Ditching Y is fine for 99.9% of 4th axis projects, including the types of items you mentioned. OTOH keeping Y unlocks a boat load of capability… for example milled primo core clamps.
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My 2 cents, I have a rotary 4th I am using. On the Marlin firmware, with dual endstops
About 4 months ago I bought a smallish NEMA 17 driven 4:1 rotary with a chuck off Amazon. ( RATTMMOTOR Reducing Ratio 4:1 CNC 4th-axis A-axis Rotation-axis, 4 Jaw K02-63mm Chuck)
I use X1 axis for the rotary.
As a 4:1, I had to set the steps/mm in the firmware for 244 steps/mm to get a complete 360 degrees.
I have the parts to setup a switch system, using 2-4DPDT switches to disable X2, and turn on the rotary, just haven’t had the time to put it together.
In the CAD/CAM designing for this, it is setup with the X dimension as the circumference of the stock. I.E. diameter x 3.142 (pi)= (X size). For an existing STL, I use CamBam with the Unroll plugin to generate a flat STL and import it. Still working on a cambam postp for Marlin, not enough hours in the day issue.
I also use the stock end stops to trap the X axis on both sides at the radial line on the stock. If you don’t it tends to move a bit.
Been running some small parts I use for the last couple of weeks. 3/4" diameter, 3 inches long, cherry dowel I make myself
With that said, running at 60 in/minute, I get a usable part in 10 minutes.
Have a vid of it running just haven’t had the time to post
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I added a rotary axis a few weeks ago. Mine’s on the Y axis. Like @JohnSherman described, I have two 4pdt switches to easily switch between the Y axis steppers and the rotary. My rotary is a roller type rather than a chuck (though I have a chuck and plans to build a chuck rotary too). I set up the rotary in Lightburn by giving it the diameter of the roller and mm per rotation. I think Lightburn handles the conversion because I don’t remember needing to adjust steps per mm. I did need to turn down acceleration so the stock wouldn’t slip on the rollers. If your use case is carving pool cues, you’ll want a sturdy chuck type I think.
I am running Marlin with an SKR Pro board. No need to change to Mach 3 or anything else unless you want to. Once I had my switches wired in (and you could achieve what they do by unplugging the two Y motors and plugging in the rotary), it took less than an hour before I was lasing round stock. You can see some of my results in my recent posts on the subject.
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@redeye_joe I sent you an email, but it returned as undeliverable
email me
bmacoubrie@gmail.com
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