considerations for successful bowden setup

Can anybody help me determine what the current thinking is for a successful Bowden setup?

I glean from what I read that 1.75 mm filament is considered the better choice. Is this true?

Also, it seems that retraction speed is very important which would seemingly rule out extruders with a reduction gear - that is direct drive extruders would be preferable. Again - am I right here.

YES on BOTH counts.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Tantillus and Ultimaker use 3mm filament and give great results. I do not believe pushing 1.75mm that far is in any way good. You want a stiff filament so it reacts quickly and does not have as much hysteresis.

Tantillus and Ultimaker both uses geared extruders because direct drive does not have enough torque. With 2.7:1 gearing you can reach 50mm/s of filament movement at 10,000mm/s^2 acceleration.

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Wow. Two opposing views from 2 veterans who have 4500 posts between them. I guess this argument definitely has two sides, but sublime points our the there is empirical evidence that 3mm and geared extrusion are both possible. I prefer to use 3mm filament, but have thus far been unable to find a satisfactory direct drive extruder for it. I guess there is room for some experimentation though. I like the idea of Bowden - if only to reduce the moment of inertia if the x carriage.

Stoffel15 has done a lot of experimentation on this in the last months and came to the conclusion that for a bowden a direct drive 1.75mm filament gives the best results.

For 3mm you must use a geared extruder.

That being said the ultimaker does seem to produce some very amazing prints.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

I think if you use 1.75 Direct drive is the only way to go for a Bowden, because you have to retract so much more filament to reduce the extruder pressure an equivalent amount vs the 3mm filament, you end up needing very fast retracts at least 50mm/s, and ideally significantly more.

However IME there is a secondary issue with 1.75 when using ABS (or worse Nylon) caused by the retract speed, the high acceleration and the relative flimsiness of the filament, if there is any gap between the drive roller and the entrance to the bowden tube in the extruder design, the filament can and occasionally will buckle into the gap as it tries to return, causing the print to fail.

I use 1.75 on my Bowden extruder and I'm still experimenting, it's possible the above effect can be mitigated in the extruder design, and I'm still messing with it, but I've been considering a move to 3mm because there it's a none issue.

This is a none issue for PLA, because it's so much stiffer.

Edited 1 time(s). Last edit at 01/31/2013 07:13PM by Polygonhell.

Thanks. It sounds like 3mm and Bowden go quite well together. I'm going to order some tubes from McMaster and start experimenting.

Although fine for experimentation, I don't like the use of "vertical" extuders for this because they need to have an unnatural mounting scheme to allow the tube to come out of the bottom. I like what I call a "horizontal" extruder, like the airtripper, but haven't found one for 3mm. Maybe while I'm experimenting I'll see if I can't redesign a wades extruder giving it a quarter turn.