My MPCNC is running since one week or so and already cut some wood. It has a work width of 1000mm x 700mm x 150mm (XYZ).
I’m having an issue with the X-axis. It seems like one Roller of the X-axis is moving a little bit quicker than the one on the other side. The Y-axis rollers are running perfectly similar.
The whole machine is screwed down to a completely planar three-ply board (27mm) and the diagonals match perfectly. So I can ensure that the outside rails are in a perfect right angle.
Also when I measure the angle with the motors off the middle rails have a right angle.
I came to the conclusion that it is a problem with the rollers after I did the following:
move around the middle by hand to ensure the angle of the middle rails is like the middle assembly wants it.
measure the distance of the rollers to the corners on both side to ensure they are equal (which they are)
enable control circuit and move only the X-Axis around 500mm to one side
measuring again the distance of the rollers
→ one roller is 10mm off
moving back 500mm
measuring again
→ distance is perfect again
I think it has to do with the belt tension (although the sound of the two belts sounds the same to me when I’m plucking them), but since I have no experience with belts and tensioning them I’m asking you people now.
I don’t think it has to do with the electronics, since I’m running the motors in series.
If you have an idea of how I can solve this problem, I would be glad to hear from you .
So first of all, thanks for the quick response!
Your ideas have proven to be very helpful. I counted the pulley teeth, theyre the same (17 teeth), I untensioned the belt and it has no bad pieces, also I retightened the already very tightly attached pulley.
So no progress. But as I was moving around the X-axis (it moves very very smooth without motors attached) I found this:
On the image I did not bend the middle rail at all, so it is indeed 10mm off. Now I’m completely confused because when I measured it before it was different, but anyways there is still a problem to solve.
Sooo, if I’m assuming correctly my right angle in the middle is not a right angle but a larger angle than 45° (right?). So according to the assembly instructions I would tighten the tension bolt B and untighten the tension bolts A. But since my tension bolt B is already very thight and my tension bolt A’s are loose I still don’t know what to do .
Thanks a lot for your help!
Best regards
TheJounezz
It’s 17 teeth on all my pulleys (I know thats not matching your design but I mean its just a thing of moving another number of steps per meter right?)…
I measured like you wrote and these are the results:
Absolutely, but that’s not my problem. I was going to do that when the mechanic aspects are working properly, which they are clearly not since I have a deviation of 2mm on one axis after moving only 100mm.
I am 100% sure that the electronics are not the problem because I did the following test: Attaching a stripe of tape to both of the X axis motors
(like this: )
Then I moved the x axis for multiple meters and whenever I stopped moving the angle of the tape was still the same on both.
So clearly it must be a mechanical problem. My assumption is that something is wrong with my middle assembly, since I cannot adjust the angle of the X and Y axis at all with the two tensioning bolts (A & B). Like I wrote her:
What board, what drivers, what current are they set to, what steppers, what current do they want, what wiring scheme, how are you controlling it.
When you chose to use things other than the kit you need to list every aspect of your build. We can make guesses all day but you will get more help when we can make educated guesses.
I’m using a CNC shield in combination with Arduino uno. Wired exactly how you described it in the assembly manual (in series). Stepper motors are no-name. First I had the voltage at 0.7V because I don’t have any information about how much current the motors want to take. I reduced it to 0.45V now because the motor drivers (DRV8825) were getting very hot (even though they have heat sinks glued on). When the motors are powered i cannot move the gantry, which means that the current is high enough for the system.
For software I’m using Estlcam, which also flashed the firmware of my Arduino with Grbl (so I’m not using your Marlin).
You were right! Has to be an issue with the pulleys or the belt.
Checked the teeth count again. Both are 17. Checked the belt again. No visible damages / inaccuracy.
Swapped the pulleys → gave me the same measurements for both axis sides. This excluded a problem with the pulleys. So I swapped the belts and indeed one of the belts was different than the others. I think it has to be manufacturing tolerances or whatever. After inserting new belts on both sides of the X-axis, the both sides were moving exactly the same distance.
After that I calibrated both axis to move exactly 100mm by adjusting the steps per rotation number.
Now I am very happy .
Although my middle angle is not exactly 90° I think I am satisfied with the movement now
Ryan. Thanks a lot for the amazing design and also for helping me with the troubleshooting!
Hey, just to make sure, these are fiberglass reinforced belts correct? If they’re steel, replace them with fiber. Steel will work harden over the small pulleys we use and break, then stretch.
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