Oozing and Retraction

26. Januar 2012

after some little talks with stoffel i’ve thought about,whats the best way to retract.

whats the actual problem with retract?
the retraction distance is konstant, so we retract these constan even if we have a traveldistance of 5mm or 5m (yes i know 5m are big, but its only to show the problem).

what the most people see what happens on retraction:
1. print normaly
2. retract
3. drive any distance with the extruder
4. re-retract
5. print normaly

what most people see what happens if retraction is not used:
1. print normaly
2. drive any distance with the extruder
3. string happens
4. print normaly

what realy happens on retraction:
1. print normaly
2. retract
3. drive any distance with the extruder, filament in nozzle is heating up constantly
4. re-retract
5. blob happens
6. print normaly

what realy happens without retraction:
1. print normaly
3. drive any distance with the extruder, filament in nozzle is heating up constantly
5. string happens
6. print normaly

thats the reason, why short heating zones doesnt ooze so much.
problem with short heating zones: you cant print fast, because you cant heat up the filament fast enougth.

another little problem, but its irrelevant, because its a very little constant: the heated up filament will blow up a little bit if the pressure is removed.

easy solution:
skeinforge: set a negative retraction restart extra distance.(dimension)
slic3r: set a negative Extra length on restart.(Print settings -> retraction)
but this will just help a little bit and on short distances! If your restart extra distance is to high, your nozzle isnt filled with material and a gap will happen.

better solution:
retract linear relativ to the driven distance. on little distances much better than the standart konstant retraction. doesnt work on great distances!

best solution:
retract logarythmic to the time that the printer need to change its position.
this solution will bring some benefits: no blobs, no strings, no ooze, no re-retraction needed.
and its irrelevant how long you travel ( not realy, because the material will dissolve and crystalyze if its heated up to long, but for retraction it works )
with some material and nozzle parameters added it will be easy to calculate the max. printing speed.

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