Retraction Tuning With Slic3r

Introduction

This tutorial will guide you through tuning your retraction settings with Slic3r.
Retraction is used in 3D printing to stop the flow of melted filament when the nozzle must be moved between islands, and a string or ooze is not wanted.
Tuning Retraction Distance, Speed, and Acceleration is an iterative process.
Bowden extruders use between 2mm and 7mm for retraction length. Longer bowden tubes require more retraction length to take up the slack. Non-bowden extruders can use less retraction length.

Basic Retraction Tuning - Distance

- Use two small, single walled objects a considerable distance apart, for instance two small hollow rectangles or cylinders.
- In Printer Settings, General - make sure "Use Firmware Retraction" is off for this.
- Start with a small retraction length (in proportion to how long your bowden tube is), if in doubt start at 2mm.

1) Set your retraction length in Printer Settings, Extruder 1.
2) Slice.
3) Print until you see how much stringing is happening, and then stop it.
3) Increase retraction distance by .5 to 1mm, slice and repeat, until stringing just stops.
Back it off if you went too far. If you retract too much then the beginning of the next extrusion can start cold (it will appear starved).

Basic Retraction Tuning - Speed

Keep that same retraction distance:
1) Increase the retraction speed in Printer Settings, Extruder 1.
2) Slice
3) Print until you can tell how well your extruder is handling the faster retraction speed. You will tell this by ear. If it is too fast then the stepper will start to sound odd (it will be going into mid-band resonance), back the speed off a bit from the danger zone (you don't want it to miss steps).

After finding the best fast speed, test slightly shorter retraction distance now - faster retraction is better retraction because less ooze blob is created while the retraction is happening (and the nozzle is stationary).

Some folks will warn you about chewed up filament if the retraction speeds are too high. Keep that in mind and watch for it. If you have that problem then it's advisable to get an extruder gear that is not so sharp that it shreds the filament... that's not the best design. Or slow the retraction speed down a bit.

Advanced Retraction Tuning - Acceleration

After you have done the above tuning, using the last gcode with the perfected retraction length and speed:
1a) Increase the extruder acceleration parameter in your firmware, compile and upload to your controller, or
1b) If you do not have Repetier firmware you can insert an [url=http://reprap.org/wiki/G-code]M204 command[/url] in your gcode to set the retraction acceleration like this: M204 R500 ; Set retraction acceleration to 500mm/s^2
2) Test again.
3) Pay close attention to the extruder motor. When acceleration is increased you may hear a more abrupt sound when retraction and unretract starts. This is desirable for quicker retract/unretract, but too much acceleration can cause missed steps.

Advanced Retraction Tuning - Extra Length on Restart

When filament is pushed through the extruder - the teeth on the extruder gear deform the filament (some worse than others).
So when the filament is retracted and unretracted, the filament may not be quite as far advanced as it had been, leading to a very slight loss of pressure.
This will show as a starved/under extruded segment where the next segment started and the unretract happened. If there are a lot of retracts in a row then there will be greater loss of pressure.
- The answer to this is to enter a very small amount in Printer Settings, Extruder 1, Extra Length on Restart. Only enter this if you need to, and start with a small amount, perhaps .1mm or less.
- If too much Extra Length is used, then the nozzle will become more and more pressurized with each retract/unretract sequence, leading to over extrusion.

To Do

- Add information about calibration objects, or links to objects? The issue with this is different extruders would require different width walls for the single wall objects.
- Examples of setting extruder acceleration in firmware