Can I increase retraction length on an E3D v6 beyond 2 mm if I have a really long Bowden tube?

Question

E3D mentions on their own wiki:

Excessively long retractions will cause issues by dragging soft filament into cold areas. [...] for bowden systems you might want to go up to 2 mm. Retraction beyond 2 mm is likely to cause issues.

I have retraction set to the recommended maximum of 2 mm, but I still get a lot of stringing and blobs. My printer is set up with a relatively long Bowden tube (500-600 mm). I wonder if I need to push my retraction setting slightly beyond 2 mm to take up some of the slack. Is the 2 mm a conservative rating (I guess they don't want dissatisfied customers with clogging problems) or is it really the maximum? Is there anything else I can do to improve retraction performance? (I already have a small coasting distance of 0.1 mm set.)

Answer 1

Yes, you can increase retraction past E3D's max 2 mm recommendation to compensate for Bowden tube stretch and slop. The reason for the recommendation is that jams will occur with most all-metal hot ends if you pull molten filament up into the cold zone. Any molten filament that enters the cold zone rapidly cools and hardens and sticks to the walls, very often forming a jam.

So, the requirement is to keep your retraction distance at the extruder less than 2 mm. Additional retraction travel that is absorbed by the Bowden tube and not seen at the extruder is fine. I personally run 2.5 mm retraction on an E3Dv6 Bowden system without any issues.

Answer 2

As pointed out by this article, you can try to:

1. Increase your speed for travel moves
2. Increase retraction length
3. Place objects strategically during print

1. Calibrating travel speed

When calibrating travel speed, you can work with:

• Maximum travel speed
• Acceleration
• Jerk
• Z-hop/lift *

I found this acceleration calculator (by RepRap Central) and video (by Thomas Sanladerer) very useful.

*' when moving at high speed, your stepper motors are more susceptible to getting de-tracked by nozzle collision from imperfections during print. If this becomes an issue, consider increasing your z-lift setting.

2. Adjusting retraction

You can be fairly certain that your filament will clog if it actually retracts past those 2mm recommended by E3D at the hot end. However - as pointed out about by Ryan - bowden retraction is based on hysteresis, meaning that that the actual retraction distance at the hot end is lagging behind the distance retracted at the cold end.

I have been battling this exact issue on my 30cm bowden tube E3D V6 setup recently, and currently use a fairly conservative ~2mm retraction. I am still getting occasional clogs while printing PETG.

3. Distance between objects

From the article linked at the top:

The faster you’re able to move to the next print position, the less time there is for filament to ooze from the hot end

As such, the distance between the printed objects will change the characteristics of the stringing:

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Answer 3

To my experience, there is absolutely no problem in increasing retraction in E3D assemblies up to at least 5 mm. Typical retraction distance for my Bowden system is 3.5 mm (ABS). Clogging may occur after a series of retracts when thermal break doesn't have enough time to cool itself down. To avoid clogging when there is a real need in long retracts (printing with filaments like PLA or PETG) you need to:

• keep amount of retracts at possible minimum
• make sure that thermal break is properly cooled. You may want to use thermal grease and extra cooling for that

Answer 4

In addition to the already excellent answers above, I want to mention that maybe a change in hotend temperature (lower) can also help reducing ooze/stringing. That is, if not other parameters prevent that.