#1 use the load test and determine if the feeder is gripping (can you manually cause it to skip steps by holding the filament while it’s trying to feed. Grinding or slipping= failure. The D4 series has a load function in the LCD menu, the i3 does not and may require user intervention for this test.

#2 If during the test of one, it grips and skips steps but cannot feed during a normal load sequence, then something is wrong in the hot end. This is when you may find a PTFE liner problem, nozzle clog, cold end jam from stray deformed filament between the feeder and the entrance to the hotend.

#3 is advanced performance testing where an extruder basically passes #1 and #2, but during a print skips steps and causes gaps and failed layers in prints. In this case, does the failures happen midway in a large roof or floor layer at higher speeds? If yes, you are simply exceeding the continuous sustained federate the PTFE liner thermally limits the melt rate of the filament- AKA slow the “F” (for feed rate) down. The MK10 PTFE lined extruder has a KNOWN sustained feed rate limit. When you exceed it on long nearly continuous infill sections, it will begin to create more backpressure and no, increasing extruder temp will not overcome this limitation. It is an inherit function of the very PTFE liner material. As a note, the i3 V2 changed extruder motors and it’s been documented this motor is not as strong as V1. As such, the max sustained feed rate of a V2 is lower than that of the i3 V1. The rule still applies, the filament drive MUST grip filament and never, ever, ever, slip or grind.

If you never pass #1, you are wasting your time with anything else. This is because any failure, be it leveling, spool drag, PTFE liner, nozzle, or just bad filament will cause you tons of grief during prints. As long as the feeder system works, then you can move on and actually troubleshoot later secondary systems (the hotend and it’s liner).

Known failures of the feeder system:

  • Subset of items that cause failure of pressure of the filament against the drive gear
  • Cracked plastic parts
  • Warped plastic parts from heat
  • V groove bearing plastic shaft cracked or broken.
  • V groove internal bearing failure.
  • Improperly assembled feeder
  • If the gear has a groove type unit (often called the aluminum gear from Monoprice) it can reduce the pressure and grip if misaligned path.
  • The i3 ships with a brass gear that while marginal, it’s not the best grip and likely will fail this test.

Other known grip problems:

  • Drive gear not tight on motor shaft
  • Drive gear setscrew not aligned to flat on shaft
  • Drive gear setscrew not aligned to clear feeder parts and/or V-groove idler bearing
  • Drive gear teeth damage from inserting metal rods and other things trying to clear jams
  • Drive gear teeth worn from Glow in the dark and other abrasive filament types
  • V groove bearing failures (this seems to be coming up recently from substandard bearings in the manufacturing)

There is also a subset of heat issues:

PLA gets soft (glass transition temp) at relatively low temps. If this happens in the feeder section, then the ability to grip and push the now soft filament into the guide and into the lower hot end section can be compromised. The heatsink and fan must be properly assembled and operational, cooling both the hot end cooling bar and providing some cooling of the motor. Again, another i3 v2 thing where the extruder motor change may have the incorrect current set at the driver and thus generates more heat than a V1. This means the motor is both not as strong and generates heat leading to failures mid print.

Potential fixes:

  • Replace broken or damaged feeder plastic parts
  • Replace feeder gear
  • Move the feeder gear forward or backwards on the motor shaft to align new fresh teeth to the filament path.
  • Replace damaged or failed V-groove bearing.
  • Upgrade the entire feeder to a 3rd party upgrade unit.
  • On i3 V2, it might mean replacing the extruder motor with a V1 or adjusting the driver current to be correct and not cause excessive heating. Even then, there still is a lower sustained federate limit as the motor simply cannot overcome the increase in backpressure from sustained higher speed infill sections of a print.