Many people are using the ikea mirrors which are slightly undersized. This is great because it gives you opportunity to wipe the nozzle over the edge of it before printing, removing most of the plastic from the extruder after priming. This is the plan:
- Instead of priming the nozzle at zero altitude, it primes it at a good distance over the platter which allows the plastic to fall instead of making a ball.
- The nozzle then returns to zero altitude to prepare wiping on the edge of the mirror. It moves up the y axis while descending so that the extruded plastic lays down instead of balling up again.
- The nozzle passes across the edge of the mirror several times while moving up the y axis. Result is a reasonable amount of plastic removed.
Note also the M104 modification to start heating the extruder while doing the homing (and auto-level) to save time.
This is not perfect but much better than not at all. I might install some steel wool or similar at the edge of the mirror to make a better job of removing the plastic gunk.
This is the custom startup gcode:
G21 ; set units to millimeters
M107 ; Switch fan off
M190 S55 ; wait for bed temperature to be reached
M104 S190 ;Start heating the extruder
G28 ; home all axes
G29 ; Auto levelling - ONLY IF YOU HAVE IT OTHERWISE REMOVE IT!
G90 ; use absolute coordinates
G21 ; set units to millimeters
G92 E0
M82 ; use absolute distances for extrusion
G1 X0 F2000; Move X axis back to zero
G1 Y0 F2000; Move Y axis back to zero
G1 Z20; Move Z axis to 20mm
M109 S190 ; wait for temperature to be reached
G1 E10 F400 ; prime the nozzle
G1 Y20 F2000;
G1 Z0 Y25; Move Z axis to 0mm and Y to 25.
G1 X20 Y25 F2000; Set feed rate and start zigzags
G1 X0 Y30;
G1 X20 Y35;
G1 X0 Y40;
G1 X20 Y45;
G1 X0 Y50;
G1 X20 Y55;
G1 X0 Y60;
G1 X20 Y65;
Very interesting! Kinda weird that there are barely any responses.
I modified it to my own values, may I ask you why you put the Z axis to 20 mm while heating?
For some reason my printer does this movement in full speed, much faster than the speed I’m used to see while moving the z axis. As I can’t find any setting that modifies this speed (in free movement?), I’d set that 20mm value to just a couple mm.
PS:
I’d set the zero value off X to 0.1, as it always hits the end switch, so 0.1mm wouldn’t mind, just go to 0 when you’re done wiping 
I gave it a fairly obscure title so no real surprise about lack of readers
I set it at 20mm because the nozzle leaks and I want to give it some space to fall away from the nozzle, especially when it does the nozzle priming. Maybe setting it close to the bed is a better way. Please let me know if you find a better way.
I did a few extra things after this post. One was to set the fan on during nozzle priming. The idea is to blow away the extruded material instead of having it stick on the side of the nozzle. It works better sometimes.
The other is to slow down the extrude rate during priming. The default full rate normally results in the extruded plastic looping up and sticking to the nozzle side. This is done with feedrate control which is important for your question.
When you do a G1 command you can pass an F parameter for feedrate. For Z axis F400 is full speed. For X/Y axis F4000 is full rate.
At the end of your script it is useful to do
G1 F4000;
which ensures that whatever happens next happens fast
Another thing I have been thinking of is to mount a small piece of metal cleaning (brillo) pad at the side and have the nozzle wipe through that. It might help to clean more of the gunk from the whole nozzle.
Hi crashmatt,
I’m afraid that second number is a bit off. Max X and Y feedrate allowed in the firmware is 500 mm/s, which would be F30000. Although that may be overrated, 200 mm/s (F12000) as travel speed is part of the new.ini config, and should work on all printers.
For the Z axis, max is 50 mm/s (F3000), but that is much too high because of friction between Z rod and nut. F400 may be a good value there, however, it depends on the mechanical setup. The default homing feedrate is 4 mm/s (F240) and Repetier Host’s Manual Control uses 2.5 mm/s (F150), for reference.
Cheers,
kuraasu
