I have been using the printer for 8 months with fairly high use and have had the usual hang-ups such as bed levelling, adhesion and filament inconsistency i.e. not all printer related but my latest problem occurred during a large print when the extruder started to reduce the flow and finally stopped.
I disassembled the hot end and inspected the extruder, first by heating it to remove filament (PLA in my case); it was during this process that I noticed dark particles in the residue and this looked to be carbon. Recently prior to this I had noticed smoke during the priming operation but had put this down as water vapour from the filament but accompanied by a slight smell, like hot oil, but ignored it.
While doing this I took the opportunity to look at the feed mechanism and removed the shaft and bearings and, to my surprise, I noticed oil from the bearings had crept along the shaft and was distributed over the serrated section. My suspicions were now that this was what was appearing as burnt deposits in the nozzle and, also being of the shaft would not help with consistent filament feeding.
My solution was to clean all the bearings and parts with alcohol (methylated spirit) and to lightly re-lubricate the bearings with a non-creep grease; in my case I used silicone grease (Amazon - Standish Trading) as this is suitable for low-speed applications and stays where it is put, incidentally, I use the same grease to lubricate the gears and put a very light smear on the jointing faces of the nozzle and heater block to improve heat transfer. The feed assembly and hot end were put back together and calibration and test prints completed and the large print (14 hours) successfully completed!
[color=#FF0000]I now refer you to my post “Blocked extruder” as this problem re-occurred![/color]
For those that are interested the following is my typical starting configuration for honeycomb filled PLA models but all new filaments are tested and settings adjusted. A word of warning, Slic3r 1.1.0 is in Beta and there are a couple of hang-ups for W8.1 when entering configuration data, needing a configuration restart to address but version 1.0 is stable:
; Repetier version 0.95F
; generated by Slic3r 1.1.0 on 2014-04-06 at 10:59:07
; perimeters extrusion width = 0.50mm
; infill extrusion width = 1.02mm
; solid infill extrusion width = 0.85mm
; top infill extrusion width = 1.05mm
; avoid_crossing_perimeters = 1
; bed_size = 205,207
; bed_temperature = 50
; bridge_acceleration = 0
; bridge_fan_speed = 100
; bridge_flow_ratio = 1
; bridge_speed = 60
; brim_width = 0
; complete_objects = 0
; cooling = 1
; default_acceleration = 0
; disable_fan_first_layers = 2
; duplicate_distance = 6
; end_gcode = M104 S0 ; turn off temperature\nG28 X0 ; home X axis\nM84 ; disable motors
; external_perimeter_speed = 70%
; external_perimeters_first = 0
; extruder_clearance_height = 20
; extruder_clearance_radius = 20
; extruder_offset = 0x0
; extrusion_axis = E
; extrusion_multiplier = 1.1
; fan_always_on = 0
; fan_below_layer_time = 60
; filament_diameter = 2.95
; first_layer_acceleration = 0
; first_layer_bed_temperature = 50
; first_layer_extrusion_width = 200%
; first_layer_speed = 30%
; first_layer_temperature = 200
; g0 = 0
; gap_fill_speed = 20
; gcode_arcs = 0
; gcode_comments = 0
; gcode_flavor = reprap
; infill_acceleration = 0
; infill_first = 0
; infill_speed = 60
; layer_gcode =
; max_fan_speed = 100
; min_fan_speed = 50
; min_print_speed = 10
; min_skirt_length = 0
; notes =
; nozzle_diameter = 0.5
; only_retract_when_crossing_perimeters = 1
; ooze_prevention = 0
; output_filename_format = [input_filename_base].gcode
; overhangs = 1
; perimeter_acceleration = 0
; perimeter_speed = 30
; post_process =
; print_center = 103,79
; randomize_start = 0
; resolution = 0
; retract_before_travel = 2
; retract_layer_change = 1
; retract_length = 3
; retract_length_toolchange = 10
; retract_lift = 0
; retract_restart_extra = 0.1
; retract_restart_extra_toolchange = 0
; retract_speed = 65
; skirt_distance = 2
; skirt_height = 1
; skirts = 1
; slowdown_below_layer_time = 30
; small_perimeter_speed = 30
; solid_infill_speed = 60
; spiral_vase = 0
; standby_temperature_delta = -5
; start_gcode = G28 ; home all axes\nG90 ; use absolute coordinates\nG21 ; set units to millimeters\nG92 E0\nM82 ; use absolute distances for extrusion\nM109 S200 ; wait for temperature to be reached\nG1 E10 F400 ; prime the nozzle
; start_perimeters_at_concave_points = 0
; start_perimeters_at_non_overhang = 0
; temperature = 200
; threads = 2
; toolchange_gcode =
; top_solid_infill_speed = 50
; travel_speed = 200
; use_firmware_retraction = 0
; use_relative_e_distances = 0
; vibration_limit = 0
; wipe = 0
; z_offset = 0