Using larger stepper motors for X and Y

Machine: Omtech K40 40watt
Board: cohesion3D
Firmware: Smoothie

Question about using different sized NEMA motors and connecting to the laser board.

I’m looking at building a larger gantry. The K40 is so small. I am assuming I can just make a larger, stand alone, gantry and connect it to all the current parts I have.

I am also assuming I need NEMA 23 motors at the smallest. I want to go to a gantry size that can use an area that is 4 foot by 4 foot = 48 in x 48 in = 1220 mm x 1220mm

I did do a draft sketch to get an idea of its size. I then realized I don’t need to make the entire thing out of T slot. I just need the gantry rails themselves, not the entire table. I will use 4x4 lumber for a table that is open deign to allow a deep Z access.

If I have read everything correctly, the laser board can only handle NEMA 17 motors up to 1 amp.

I have to use an external stepper driver to power larger amperage ones. In a pic it shows connecting to the row of white colored plugs in the middle of the laser board that say “expandable”.

So does that mean I would need to unplug the current plugs for X and Y at the top of the board, and then use an external stepper driver for each NEMA and connect to the expansion white plugs only?

I am assuming the black plugs at the top are only for 1 amp NEMA 17 motors.

I’m not sure if I need to use 2 NEMA 23 motors per axes or not. If I have to use 2 motors per axes movement, would they just be wired together into the same expansion port? Meaning an external stepper driver for each motor, and then connecting the wires from each driver together into the same white plug so it controls both motors from the same plug?

I am trying to learn how to build a gantry and don’t want to mount the laser tube on the rail. Partly to keep weight down and partly because I think the water weight will cause issues when it is moving and could cause the laser tube to break. Plus it puts smoke directly at the laser tube and mirror.

I have an upgraded fan and air and water pump already. I also have an upgraded “beam buddy” that I have not installed yet. I know it weighs more than the K40 focal tip. So my rail would just have the head and power cables and air line on it. That should be minimal weight.

Yes, the axis expansion plugs towards the middle of the board are the signal outputs that you would wire to separate external stepper drivers(and these will need their own power supply)

You should not wire two stepper motors off a single port. Can yes, but not recommended. On gantry setups running parallel motors, you will typically run the secondary motor mirrored, meaning the same signal is output from the board to the driver but in reversed fashion. The two motors run in opposite directions. This all depends on how you mount/gear the motor drives though on your particular machine as there are ways of doing it where you run parallel motors that are NOT mirroredboth run in same direction). Don’t quote me(as I literally just bought my own C3D board building my own machine) but I believe the C3D board has the option to use one of the extra axis ports(A or Z) in parallel for a dual motor axis setup. I am going through all the documentation for the setup myself right now.

Hoenstly NEMA 17s are probably sufficient for the weight of that gantry. Just get beefy ones with a high moving torque. I’d only go to 23s if you were doing something that had a lot of axial strain on the gantry like a CNC router. I also strongly suggest that you use one motor per axis, a dual-shaft motor for Y, and do shaft extenders and belt drive - reason being is if one of the motors loses steps or binds for whatever reason all of a sudden you have a potentially high power laser beam going somewhere with a misaligned mirror. With a CNC router or mill this isn’t a big deal, just rezero your machine and keep going (after a gratuitous donation to the carbide graveyard, probably). But with a laser this is far more dangerous because of the mirrors. It’s better to have a rigid coupling between both sides of the Y axis. I can’t see a situation where you’d ever need two motors on X, either. If you do end up needing a 23, it’ll be in Y, and X can almost certainly remain a 17.

As far as the tube goes, it emits a nasty amount of the bad UV radiation when energized so it’s best to fully support and enclose it anyways. I wouldn’t be too worried about the water weight, as with two stock tube clamps the tube is designed to be able to hold its own weight plus coolant.

If you do decide to go with external drivers you will need a set of these:

Good luck. Post pictures during the build, i’m interested to see how this turns out

Thank you for that. I was thinking the row of plugs would be for separate stepper drivers. I’m still trying to see what is best for a gantry so I don’t know which way to go yet. I have looked at belt drive, gear, and screw rods. I think the screw would be the most accurate.

I am trying to learn about these things. It appears that on other online places they say NEMA 17’s are only meant for light weight movement. 23’s are for heavier weights. On some builds, they say NEMA 23 is the minimum to use for gantry’s larger than 3 feet.

I have looked at belt drive, gear, and screw rods. I think the screw would be the most accurate.

I saw one on amazon that uses a Linear Rail.


I figure that would be less friction and with the screw, it would be more precise. I would only need 1 motor that was as well. I had seen other builds using 2 motors to move the axes. I’m seeing a lot of stuff online about belt issues. Like belts being loose, or jumping teeth, or breaking. Some are showing in larger distances, belts will distort the image because it is moving so far away.

I originally looked at 60x60 extruded alum. Then I saw these linear rails. I would think the rails would allow smoother movement.

I am not set on the size of the gantry yet. I would like to be at a 4’x4’ minimum size. Going to a 4’x6’ or 4’x8’ would be nice. To do that I need to change the table altogether and make it vertical.

If I go larger and have to make the gantry vertical, I was thinking of how a sliding door or window holds in a track lip. The work pieces would fit in a tract so they would not fall and be able to be adjusted for the laser focal point. It would be like rotating a normal table 90 deg.

I should have room for a 4’x4’, but would have to go vertical if I go any bigger. By doing that, the stepper motors would have larger weight to move as gravity

In my draft pic I didn’t bother including any covers. I will be boxing everything in so suction works to pull the smoke and to protect the laser tube.

I already have a much larger fan that is 8" that I had to reduce to the 4" for the K40 size. I found on low speed, it has enough draft to close my room door, even with the lid closed on the K40. (I’m in a 15’x12’ room) It shows 740 CFM so it should be fine for a larger gantry surface.

I would probably us the insulation panels with the alum backing. I was thinking of fiber board used in kiln making. (I had been into glass work) They are rated for up to 3,000 deg F. I was thinking along the lines of a complete encasing so in the worst case scenario of a fire, with the panel shut, a fire would not be able to spread. Temps could reach to 3,000 degs and it would still be cool on the outside. That way there is no risk of anything in the room catching fire. That is just over making it for safety. It would be like making the entire gantry table inside a kiln so if something happened, keeping the door shut prevents a fire spread. Wires and air/water lines could be cast in access holes using refractory cement so they are “plugged”. The only opening would be for the laser line entering the area. A simple plug could be used in a fire to plug it. Just like how the access holes on larger kilns are. They have a removable plug you can pull out to look in. If a fire happened, power is shut off and you can just place the plug in the hole by hand. Then the entire thing is sealed off.

On my orders from here, I do have the set of cables fro the stepper drivers. I only have 1 driver as I was brand new to these things and bought just 1 encase I was to upgrade later. I didn’t realize at the time I needed 1 for each stepper motor.

Yes ballscrews are far more accurate and repeatable than belt drives but don’t come without their drawbacks. Linear trucks/rails and ballscrews require frequent lubrication. Such frequency is dependent upon sustained use, speed, and operating temperature. Without lubrication the trucks will each away at their plastic liners that transfer the balls, and the screws will just wear down.

Also note that ball screw nuts are not created equal. Ones with preload to help eliminate backlash aslo induce more drag into the system and require more power to run. it is a tradeoff. If your drives are powerfull enough to disregard this, then preloaded antibacklash type nuts are recommended.

There are always tradeoffs in any of this. While belts do stretch/break, they are cheap and easy to replace so just keep that in mind. I own/operate a full machine shop with CNC equipment and for the cost of one of the ballscrews in my bigger machines I could probably buy 2-3 DOZEN good K40 lasers

And yes you need one drive PER stepper motor/servo. There are drives out there that run tandem motors but they’re usually big frame stuff (N34+)

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.