Primo walking off left in x axis

I have just finished building my Primo. I can draw with a sharpie pretty cleanly, but when I attach an extruder and print the print walks off to the left in the x axis pretty severely. I made a spiral vase print to see if it was coming from the movement between layers, but it also walks off doing a spiral.
I have it built x48 x y24 x z14, with 3/4" conduit. I use a separate bed that has 5" of vertical adjustment but is stable. I am using the v1 dual end stop firmware and the v1 tft35 firmware. I am printing at 25mm/sec.

The model in the photo should be symmetrical!
Any help or ideas on what could be the issue are appreciated.

This photo is drawing with a sharpie at 60MM /sec. a few wobbles, but pretty clean for 60mm/sec.


I know it is nearly a running gag, but did you check the grub screws? One might be loose so that the axis does not travel as it should. At least that’s what I had at the beginning, it was not really noticeable, because the one motor dragged the other one behind.


Yes, Thanks Phillip. I read that possible cause on the forum before I went home for lunch, I checked and found some loose grub screws, even one pully on the y1 stepper has lost both screws! I believe that is going to be the problem now. I will give an update tonight when I get home and try another print (after I locate a spare set screw. Does anyone know what the size is for the set screws?

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Yup! The alleged Mpcnc moster " The dreaded Grub screw" can easily take down a newbie!
I reprinted the same model wirh what 3mm filament i had left (about 20 inches ) and the 70mm result rivaled myTevo Black widow. Absolutely stunning! I would have never expected this machine could achieve this precision. (pics dont do justice)

THanks for the help!


That is an awesome printer. Nice work.

Thanks Jeff, but you deserve the real credit!! Thanks for this awesome design!

It would be a lot less funny if it weren’t so dang true! Being able to chuckle at yourself is one of the keys to surviving life in general, much less building and maintaining any sort of precision tooling. It’s akin to tech support guys having the first couple of questions being things like “is it plugged in?” or “do you smell smoke?” Seemingly painfully obvious questions, but if you think about it, they are simple, fairly easy/quick to answer, and absolutely nothing else will do any good if those questions don’t get the correct answer. So yes, checking the grub screws is something of a running gag. But it’s a potentially quick and simple fix, and if it is the culprit, nothing else you do will work anyway.


Ryan designs this machine all by himself. I just spend too much time making jokes in the forum.


Oh, then thanks Jeff for the props!
Sorry for the confusion Ryan if you are reading this, I am pretty new to the forum. And again THANKS FOR THE AWESOME DESIGN.

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After tightening all the grub screws It made a good print, but the very next one walked off again. Turns out that the screws had loosened again! I figured, thee motors are cheap, the pulleys are cheap, I’ll never use them for anything but this machine and they will go out eventually, so…
Epoxy the dang pulleys on the shafts and be done with it!! That is what I did with no regrets! Thing is printing awesome now with no issues from the pulleys, no lost steps, nothing wrong! Hallelujah!!

400mm x 200mm tall octopus printing in vase mode at 75mm second with a 2mm nozzle. No issues.

see video of path here

Can anyone foresee any issues with the epoxy?

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Epoxies pulleys!? Nice. That should fix it. The more common solution is locktite. AFAIK, we have used two kinds of pulleys so far, both 16T, but we used to use 6mm and now we use 10mm. So I think you’re good. If those ever end up in a parts bin, you could make someone very frustrated. From now on, any alignment will have to be done on the motor mounts.

Yea, I will probably forget in a few years that I have made a one piece motor/pully and drive myself crazy trying to get them off for another project!
What do you mean by “alignment will have to be done on the motor mounts”?

Thanks for the feedback.

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The location of the belt along the shaft isn’t always the same. Sometimes you have to move it closer or farther from the motor to line up with the place the belt tracks.

Yea, I see. Luckily mine ended up in line with the idler pulleys. My primo printed parts are also very good and accurate which has helped a lot.