Cylinders aren't round

[steve220]

Looking to the group (again) for some feedback and suggestions on an issue I've encountered printing round objects. Cylinders aren't round and have flat spots on them. This print shows what I'm talking about:

I don't know if this is a recent problem or not since I only found it when trying to print cylinders that are meant to go through holes in another print.
Looks like a classic backlash issue, but I'm not sure how to go about correcting this on the M2. I do have the nema dampers on the X and Y motors. Steps I've taken so far:
-Tightened belts (they didn't feel loose though)
-Ensured the gears on the motors that drive the belt are tight on their shafts

Any help is appreciated!

Edit: Just as a test, I removed the dampers, but it had no effect. Test prints were identical.

[jimc]

Anything loose on the hotend? Can you grab the nozzle and wiggle anything?

[ksevcik]

Are the flats in the x or y direction? The problem axis is always perpendicular to the flats.

[steve220]

Hotend is all tight.
The flats are along (parallel to) the X axis, which means it is a Y axis issue. I can find no slop or play in either axis.
I also cleaned and lubed the axis rails to eliminate that as an issue.
Printing through OctoPrint and connected directly to the computer via USB produce identical results.
Went back to some of my earliest models that have round components and the flat is there also. I just didn't notice because it is pretty small and I wasn't trying to fit any pieces together. The difference in diameters of the various round things I've printed is around 2% with the X axis being the correct diameter and the Y axis being smaller. Even though the Y axis prints smaller, the flat spot is creating a bulge at the 10 and 4 o'clock positions.

My other printer has a firmware backlash setting that can be tweaked. Is the M2 similar? I don't find something like that anywhere I look.

This is the calibration object shown in my original photo:

EasyCalib3.stl

(732 KiB) Downloaded 360 times

[Jules]

Check the Y axis rails and see if those need lubrication or cleaning as well. I've had an extruded thread of filament get caught up in the grease underneath and cause a little sticking.

[ednisley]

Ensured the gears on the motors that drive the belt are tight on their shafts

Look very carefully at the position of the tiny screw that locks the pulley to the motor shaft: it should be exactly in the middle of the flat on the shaft.

You can just barely see the screw behind the belt in this picture:
https://softsolder.com/2013/05/07/m2-vs ... culations/



When the screw isn't centered on the flat, then you can tighten as much as you want and the pulley will still flop back and forth as the shaft reverses direction. Worst case: it's not on the flat at all, which means it became loose enough to gouge a furrow(*) around the shaft.

The best way to get the screw in the middle of the flat:

• Loosen the screw until you can turn the pulley on the shaft
• Slowly tighten the screw while wiggling the pulley
• The wiggle should decrease as you tighten the screw
• When you can't wiggle it any more, tighten firmly

A dot of threadlocker on the screw (you must take it completely out) will prevent that problem from happening again.

(*) If the screw isn't on the flat at all, then you must remove the pulley, file the burrs off the shaft (and maybe the inside of the pulley), and touch up the flat before continuing. Very deep gouges will prevent you from removing the pulley without applying brute force.

[tk1138]

I have the same issue as well. It's subtle most of the time, but shows up on cylinders especially when it prints the inside and outside in different directions. My calibration cubes also show a bit smaller in the Y direction.
I've tried tightening the belts, mounting, checking the pulley lock nut location, as well as replacing the Y motor. No luck yet.
Looking at the Makergear printed right spool holder, I think the issue is present on that part too, assuming they wanted the holes printed circularly.

Maybe it's a firmware setting, but I've had the issue on both the default Mark E firmware, and the dual FW for the Geeetech LCD (though I don't have an LCD).

Other than this issue, my printer is running great.

[jimc]

Odd. I have 3 m2's here and the parts i print all the time are round. Nothing is ever out of round more than .005". Its gotta be something else on your guys printers. I have the rubber isolators on 2 of the printers also and there is zero difference between with or without

[tk1138]

What slicer software are you using? I'm using Simplify3d.

I tried lowering the xy jerk to 1, but the issue is still present. I'm running a test print with two different speed settings to see if a lower speed will improve things. It seems like the Y axis is lagging the X just a bit.

[jimc]

i am using s3d as well. my speeds arent smokin fast but they arent slow either. i mostly print petg and with that i am at 3600mm/min.