X & Y distance irregularity - same components and steps_per_mm

Hi All,

I'm in the process of configuring a MendelMax 1.0.

Just a background on my hardware, I am running using;

• RAMPS 1.4
• NEMA 17 steppers (1.68A max) - 1.8 degree/step
• A4988 stepper drivers (jumpers set to 1/4 step)
• T2.5 pitch pulleys (16 tooth) - X & Y axis
• T2.5 Belts - X & Y axis
• 3/8-12 ACME Precision Lead Screws - Z axis
• Budaschozzle 0.5mm Nozzle (Not sure of version, assuming < 2.0)
• Marlin Firmware
• Slic3r

Based on Prusa's calculator, my steps_per_unit for X & Y should be 20.
This is reflected in my firmware.

Quote
#define DEFAULT_AXIS_STEPS_PER_UNIT {20.0,20.0,377.9527559,203.6485236} //X,Y,Z,E0

Upon printing some cubes designed in Solidworks, exported to STL and sliced with Slic3r, the dimensions are out on the X axis.

Below is a list of the outcomes;

1. 10mm Cube: X: 10.50mm, Y: 10.50mm
2. 20mm Cube: X: 19.59mm, Y: 20.09mm
3. 30mm Cube: X: 29.47mm, Y: 30.06mm
4. 30mm Cube: X: 29.76mm, Y: 30.46mm
5. 30mm Cube: X: 29.65mm, Y: 30.27mm
6. 30mm Cube: X: 29.47mm, Y: 30.06mm (the best)
7. 30mm Cube: X: 28.83mm, Y: 30.15mm
8. 40mm Cube: X: 39.25mm, Y: 40.24mm
9. 40mm Cube - X: 38.64mm, Y: 40.62mm

As you can see, X is averaging 98.8% of it's size, whilst Y is averaging 101.3%.
Is this normal for a 3D printer?
What settings within marlin can be tweaked for this?

-edit: I should have mentioned thathat every measurement was averaged over 3 points;
Bottom, above raft, mid, and around the top layer.

Edited 1 time(s). Last edit at 10/04/2015 11:52AM by larnert.

Sounds like you have backlash in your X axis. Check that the pulley grub screw is tight and the belt is not slack. Also I suggest you increase the microstepping to 16 and steps/mm to 80.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The first cube tells me it's likely over extruding, and based on the other prints the x may have some backlash. Check if the belt is tight, the x idler doesn't wiggle on back and forth motion.
It can also depend on where you measure, at the corners or in the middle of the cube. If it blobs in the corners it may be from retraction length and or speed, or the Vxy-jerk may be too low.
If you calibrate the printer, which can be very time consuming you should be able to get the dimensions within 0.05 to 0.1mm. Things like backlash, over or under extrudion, print temperature, velocity, acceleration and jerk settings, extruder performance especially bowden can all have an effect on print quality and dimension.

Thanks all.
I will attempt tightening the belt. The pulley grub screw is tight and is meeting the the shaft "key" (flat cross section of motor shaft).

Will report back tomorrow!

Edited 1 time(s). Last edit at 10/04/2015 11:56AM by larnert.

The grub screw / set screw on the X pulley has simply vanished. I assume it vibrated out and was swallowed by the abyss which is my house.
I have replaced it and but some blue thread-locking paste in there to hold it.

Hopefully this solves my issue.

Thanks for the help.

Thanks for following up. I'll remember to put some thread locker on those screws!