just built my MPCNC and have encountered 3 problems

First off, I want to commend the designer on a fantastic machine. I am extremely impressed with how well the parts were designed for printing and fitment.

So here are the specs for what I am running. Machine is using US EMT conduit (24.5mm?) and is a 48"x48", Z is designed for 6". I did not purchase any of your parts but I did follow your list with the exception of the stepper drivers. I am currently running the A4988 drivers (16 microsteps) and the RC7 firmware from this site as the RC8 had “issues” at the time. I have endstops set for MIN on all axis and everything seems to function perfectly.

The problems I am encountering are as follows:

  1. The stepper drivers are running pretty hot to the touch. Motors are fine with regards to temperature.

  2. When the center section passes over the middle of the bed, I get a lot of shaking/jittering in that area. Does not seem to show up in the corner regions. All belts are tight, but the long screws in the center are very loose.

  3. This is the biggie. I am running a pen to print the Crown picture. When printing, the system will have a noticeable surge pattern as it moves. It’s not really obvious, but you can hear it as it moves. One a small print (approximately 75mm across) it barely noticeable. When I scale up the picture, to say 500mm across, it is very obvious. the movement will go from very slow to fast at various area of drawing. I did change the number of steps to accommodate for the different driver, but I cannot figure out what else would be causing this. I am printing over USB via Repetier and also Octopi, both have the same results.

And assistance would be greatly appreciated. Thanks!

Thanks for the compliments!

US conduit (3/4" ID) is 23.5mm, did you print the right parts?

  1. Did you set the current on them? I’m not sure what it is for the a49’s anymore but you should set them for your steppers. They will be hot we run the DRV8825’s pretty high and they are reported to run a bit cooler. You could always switch to series wiring to help with heat.

2)See the above conduit question. Also make sure you aren’t running the bearing on a seam of the conduit it tens to be rough on some brands.

3)Hopefully the surge is actually the acceleration happening. hard to say without seeing/hearing it myself.

You are correct on the size, it is 23.5. I did check the voltage and it is 1.16 for the X and Y. This is the same as I have been running on other 3d printers that have dual motors on a single axis. I am making a video to show it running, from what I can tell it seems like it really slows down in curves and circles.

here is a link to what is happening

@Altrex, you mention that your steppers are set up the same as on other printers, but unless the drivers and motors are the exact same models, it’s not the motor configuration that determines what the voltage should be. The voltage should be determined by the max current for the motors. There’s a good pololu video that explains how to determine what to set it to. I would recommend making sure you have the voltage (vref) set correctly. Heatsinks and a fan blowing on the drivers can help, too.

the drivers and ramps boards are the same, the motors are different though. I haven’t found any videos that explain the vref for a parallel motor setup yet. One thing to mention, when I run the mpcnc from pronterface or repetier, it does not slow down. it appears like the data is taking too long to get processed for the Crown drawing. I am wondering if it has something to do with the USB connection or some buffer setting.

Post your gcode file please.

I just took a look at the video - that looks like a gcode problem. Have you looked at the gcode? Look for lines where the F parameter is changing from fast to slow values (like so: G1 X120 Y60 F1000 / G1 X150 Y70 F300). The lines probably not be right next to each other. You could do a search for F, or even just scan by eye and see if the F value changes a lot.

Try changing your arcs settings. Either turn them on or off opposite of what you are running in the vid.

I agree that it must be a setting somewhere. I tried a dxf for a simple part and it obvious that the arc and circles are the slow down. So where is this arc setting you speak of?

In estlcam. look through the settings and it is a checkbox.

I changed the estlcam value but it just make gcode files with weird circles. My gcode does not show and changes in the feedrate. I am coming to the conclusion that its in how the firmware is handling the arc movement. Can anybody here make a big fast circle?

How big are you making it I can try it on this end with the same size.

the Crown i am printing now is 22" wide. please let me know how it works for out for you. thanks

I don’t have one with a build area that large biggest I can go is 15", I can try it on the LowRider though.

Please let me know what you find out.