Looking into making a rotary bed for my OMTech K40. I’m pretty sure the stock controller runs on 24VDC but many of the beds I see for sale seem to specify 12V for their motor as well as the various DIYs I’m looking at.
I could unplug a motor and test it myself but you know, I’m lazy. What voltage NEMA17 should I be shopping for?
OK, quick research shows the NEMA17 spec itself calls for 12V. Does that 24V controller put out 12V for the steppers?
The real controlling spec for stepper motors is current. Find the max current and set it on the stepper controller, and then 24V is fine. Many 3D printers have moved to 24V. It’s a great idea.
However, keep in mind that the power supply has to be able to supply all the current you are trying to draw from it.
In this case the controller is the stock that shipped with the K40 a month or two ago. And I’ve offloaded the 24v load to a meanwell PS.
Gonna proceed with the NEMA17 I see called for…
Oh good, you’ll be set then! 
More on that 12V specification: That basically means that 12V is the max voltage you can put across the coils without limiting current; if you put 12V across the coils they will pull the maximum rated current.
You’ll want a motor with a similar specification to the Y motor in your K40 if you are using the Y controller on the control board. This is because the current limiting will be set by a resistor that is soldered to the board. If you have trouble figuring out the specification for your existing Y motor, feel free to post a picture of the back side of it with the writing visible and readable.
(There are other configurations besides re-using the Y axis; some folks have a control board with a separate A axis for the rotary where the rotary motor can have a different configuration for current because it’s using a different stepper driver chip.)
And don’t forget about the resolution of the stepper. My K40 came with 9 deg( 400 steps / rotation ) instead of the standard used for 3D printers/etc which is 1.8 deg( 200 steps ).
gonna get a picture of one of the existing steppers. more to follow
so much for that. jammed my camera in there every which way and I can’t see any sign of a label on any face of either motor. between the two of them I think I saw every face, so I’m not going to go so far as to remove one
yeah, the ones I see spec for other rotary beds all seem to be 0.9° also. and if that’s not right I think I can adjust it in K40 whisperer
You have to adjust Y step ratio for the radius of whatever you are cutting anyway, so the resolution of the A stepper doesn’t really matter that much, and 400s/r (0.9°) motors typically have lower torque than 200s/r (1.8°) as far as I know. Current matters more.
@donkjr found that his Y motor was a 1A motor:
That makes it reasonably likely that another 1A motor is reasonable for your A motor hooked up in place of your Y motor.
Do note that you should never connect/disconnect motors under power — it can kill the driver to do that. You probably wouldn’t anyway, but if you plan to swap out whether the Y driver is connected to the Y stepper or the A stepper, I just wanted to make sure you knew not to try to hook something up that would let you swap while power was turned on.
on one hand, this is not my first rodeo and I definitely know about turning things off before you start unplugging and plugging things
on the other hand, you’re talking to a guy who wants filled his RVs gas tank with fresh water so anything is possible
From what I recall, my X motor was ~1A and my Y motor was .8A or something like that and I figured it was because of 2 reasons.
1-The 24V in the LPS was pretty weak so they kept the stepper motors low power
2-the X axis takes more strain while engraving and the Y axis generally moves less.
If you want to beef up your 40 watt laser pop a VMS controller in to it LX4s is the one you want to run a full motorized bed with autofocus functionality. It will not only run your bed but totally turbocharge every function of your laser, increase the speeds dramatically and give you superb results. I run that board on a 100 watt laser but it will work just as well on a40,50,60 and even a150 tube. It doesnt seem to have a limit.
With a motorised bed you should be using a stepper motor with a planetary gearbox unless you are just using 3mm wood on top, that stepper gets a lot of wear on it without one.
Here’s a good one but you will need a controller like above to run it at 24 volts, If you decide to use an electric motor instead then use a separate PSU and not the LPSU, as it’s not powerful enough to run the laser and 3 steppers.