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CFS Maintenance — K2 Plus Combo

Regular maintenance of the CFS (Color Filament System) keeps filament changes reliable and prevents clogs, failed cuts, and feed errors.

Maintenance Schedule

Interval Task
Every 500g of filament Clean the purge chute
Every 1kg of filament Inspect and clean the cutter blade
Every 2kg Lubricate the CFS feed rollers
As needed Re-run cutter calibration
After any filament jam Full inspection before resuming

Cutter Maintenance

The cutter is the most maintenance-sensitive part of the CFS. A dull or misaligned cutter causes failed filament changes.

Cleaning the Cutter

  1. Unload all filament from the active slot.
  2. Navigate to the cut position manually using the touchscreen or via Fluidd console: 
    G90
G1 X10 Y200 F12000  ; move to pre-cut position
  3. Use a soft brush or compressed air to remove filament debris from the cutter blade area.
  4. Check the blade for nicks or buildup.

Re-running Cutter Calibration

After cleaning or if cuts are inconsistent, re-calibrate:

  • Touchscreen: Settings → CFS → Cutter Calibration

The calibrated cut_pos_x value is saved to the SAVE_CONFIG block in printer.cfg: 

#*# [box]
#*# cut_pos_x = -7.40

Check this value is within the valid range: -5.5 to -9.5 (as defined by check_cut_pos_x_max and check_cut_pos_x_min in box.cfg).

Purge Chute Maintenance

Purged filament collects in the chute area at X=133–160, Y=378. Over time this can build up and cause the wiper to miss.

Cleaning

  1. Cool the printer fully.
  2. Open the front enclosure panel.
  3. Remove any accumulated purge strings and blobs from the chute area.
  4. Clean the silicone wiper pad (at X=160–170, Y=374) with IPA if filament residue has built up.

Feed Roller Maintenance

The CFS units use motorised rollers to push filament. Debris on the rollers causes slipping and under-extrusion during filament changes.

  1. Open each CFS unit.
  2. Clean the drive rollers with IPA and a cotton swab.
  3. Apply a small amount of PTFE-safe lubricant to the roller shafts if they feel stiff.

RS-485 Cable Check

The CFS communicates with the printer over an RS-485 cable on /dev/ttyS5. If the CFS stops responding:

  1. Check both ends of the RS-485 cable are seated firmly.
  2. Restart Klipper: /etc/init.d/S55klipper restart
  3. Verify the bus is active: ls /dev/ttyS* — /dev/ttyS5 should be present.

Filament Sensor Calibration

If the filament sensor (filament_switch_sensor filament_sensor on nozzle_mcu:PA11) gives false positives or misses runout:

Check sensor status in Fluidd under Sensors → filament_sensor.

The sensor pin is ^!nozzle_mcu:PA11 — the ^ is a pull-up and ! inverts logic. Do not modify these unless you have replaced the sensor hardware.

CFS Troubleshooting Quick Reference

Symptom Likely cause Fix
Filament not cut cleanly Dull blade or miscalibrated cut_pos_x Clean blade, re-run cutter calibration
Filament not feeding to nozzle Roller debris or RS-485 disconnect Clean rollers, check cable, restart Klipper
BOX_CHECK_MATERIAL_REFILL triggers constantly Filament sensor false positive Check sensor wiring and pin
CFS not responding in Fluidd RS-485 bus fault Check cable, restart Klipper
Purge string not wiped off Silicone wiper dirty or wiper position off Clean wiper, adjust clean_pos_* in box.cfg
Cut position error after factory reset SAVE_CONFIG block wiped Re-run cutter calibration from touchscreen