Prusa i3 Common Issues Troubleshooting

By | August 5, 2013

1. ATX Powersupply keeps turning off in the middle of a print.

  • Most power supplies require a load on their 5V rails, which one is 5V? Any yellow wire to black ground wire will be 5 Volts. (Red to black will be 12Volts) You can either use high power 10 Watt 10 Ohm resistors, or like me, you can just plug in an old CD Burner.

2. PLA prints are coming out very brittle, and they break easily.

  • You need to increase the nozzle temperature so that there is better adhesion between layers.

3. First layer is not sticking to the heated bed.

  • I’ve found using a 1:10 PVA glue (Elmer’s will work fine) to water solution, and just brushing it onto the bed. Let the glue dry, and then print soon. If you wait too long, it will lose its stickiness.

4. Prints seem to jump and skip steps. This will look like at a spot, the print will shift in the X or Y axis.

  • There can be a couple of causes for this.
    • Your stepper motors or motor driver board are overheating. You’ll need to adjust the stepper motor current to the lowest amount where it will still run. On a RAMPS board this can be done by adjusting the Vref. Detailed instructions can be found here: Look under “11.4 Pololu Stepper Driver Calibration”
    • The default acceleration in the RAMPS Marlin firmware is stupid high, so it could be too fast for your machine. You can go into your firmware (Configuration.h), and adjust the following settings. My adjusted values are in red, I put them to 2% of the default values.
      • Original Marlin Defaults
        #define DEFAULT_MAX_ACCELERATION {9000,9000,10,10000}
        #define DEFAULT_ACCELERATION 3000
      • My Version
        #define DEFAULT_MAX_ACCELERATION {180,180,10,200}
        #define DEFAULT_ACCELERATION 60
    • To detect any issues with the driver boards themselves, try switching the X-axis & Y-axis boards with those of the Z-axis and Extruder.

5. There are blobs in the print.

  • I’ve found adjusting the default extrusion width in Slic3r to 1.2 times the layer height. For a layer height of 0.25mm I use an extrusion width of 0.3mm. This is not an exact science, but a system that seems to work for me.

6. First layer looks awful, kind of like spiraling filament, that doesn’t adhere.

  • The Z-home is too far from the glass, adjust the Z-endstop so the nozzle is closer. Use an index card or piece of paper to do the “friction test” where you drag the paper under the nozzle, and adjust the z-home until you feel friction.


2 thoughts on “Prusa i3 Common Issues Troubleshooting

  1. Mike Spano

    Great idea about the acceleration. I think that is what is causing my issue. I’m going to check when I get home.

    Question: I double check the z-axis and how close it gets to the bed all the time since I’ve had issues with it hitting the bed and “unscrewing” itself. Anyway, I finally got the endstop perfect but for some reason when it homes at the beginning of a print the z will go just barely above the glass, stop and then raise a bit for heating. The problem is that when heating is finished it doesn’t go all the way back down to the glass and I find I have to try and manually level while it is printing the skirt.

    I have checked and rechecked/calculated the z-axis for proper calibration and it seems to be measuring correctly.

    Is there an option in the firmware for how much it lowers or raises when heating? Maybe it isn’t telling it to raise 5mm or so but only lower 3ish? Is that possible?


    1. abhilash Post author

      Hey Mike, sorry for the late response, but I’ve found that I’ve had to re-hone in my z-axis before every print. There are some reasons for why the machine can’t remember exactly where to start from each time.
      1. Remember the switch we use for the Z-endstop has a thin metal flap that might not hit the switch consistently, also the switch is attached by a ziptie so there is some room for wiggle.
      2. One thing we can try to improve is the way the screw (that hits the switch) is attached. Someone smarter than us has made a part on thingiverse that I recommend you try, all you need is some washers and a spring.
      3. In Slic3r we can add Custom G-Code. This is in the “Printer Settings” tab. Currently I have the following code (after the semi-colon is a comment that says what each thing does):
      Start G-Code:
      G28 ; home all axes
      G92 E0 ;reset extruder
      G1 E3 F1200 ;Prime extruder 3mm
      G1 E2 F1200 ;retract extruder 1mm
      G92 E0 ;reset extruder

      End G-Code:
      M104 S0 ; turn off temperature
      M140 S0                   ; make sure the bed is turned off.
      G28 X0 ; home X axis
      M84 ; disable motors

      Hope all that helps Mike, enjoy printing, this is a solid machine, only quirk is that it’s kinda like Fonzie’s jukebox, we have to fine tune it.


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