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Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Prusa i3 "Tweety" Parametric Compact Extruder

by thinkyhead Aug 18, 2013
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You might want to have a look at my how-to , to improve reliability of this motor https://sites.google.com/site/jfpayeur/motormod

Hi ! Thanks for this very nice work. This is the first design using this motor which works well for me for printing ABS (all the previous ones I tried had asymmetric idlers with a single tightening screw, which did not work for some reason).
What retraction parameters do you use ? I currently retract by 5mm at 10mm/s, but it's fairly slow. Do you have preferred parameters ?
Thanks again !

I've been using Cura for most of my slicing, and it has the feature of planning moves to follow the shape of the print, which distributes ooze across the print a bit better (though of course it's no substitute for well-calibrated extrusion). I do still use a small amount of retraction, 1.5mm at 15mm/s (so each retraction takes 1/5 of a second), but I've been getting occasional small blobs on prints (in white PLA) with these settings. So I might go for 2 or 3mm.
Basically, start calibrating with no retraction and get your flow to a place where there is very little ooze, then enable retraction starting at 0.5mm, then work your way up, in 0.5mm intervals, until you see no more blobs on your calibration object. I print a few little objects to test: flow, then ooze, then bridging.
Temperature and the material will also affect how much expansion there is in the melting chamber, and how much ooze is produced. So for each new roll of filament it's good to determine the minimal temp needed to get good extrusion and adhesion, then set that value in your slicing software while testing ooze. When you increase speed you will also need to increase temperature, but figuring out the temperature at average speed — 40mm/s — will give you your baseline.
For PLA, cooling the filament as quickly as possible gives very noticeable improvement. The Tweety fan duct is still a work in progress, and the current version doesn't contain airflow as well as it could. I will be creating a new fan duct that fixes the problem and directs air both at the top of the nozzle and onto the top of the print below the nozzle. In the meantime, duct tape can probably be used to make airflow better.

Thanks for all these info !
About the fan duct, I made a custom adapter arm to use a fan shroud I had in store: http://www.thingiverse.com/thing:61407http://www.thingiverse.com/thi... prints do not look perfect yet, but I still have to calibrate things for this new printer :)

Fan Duct V3 for PLA