How to REALLY fix blobbing: Pre-retraction!
Posted: Wed Jan 28, 2015 11:40 pm
I posted a thread about this here on the KISSlicer forums.
The theory is this: Retraction causes blobbing because no matter how fast you retract (and you actually want to retract SLOW to reduce stringing), it can never be fast enough to defeat the hot end's tendency to ooze, unless you're printing thin layers at 20mm/sec. (And why have a Delta if that's all you're going to do?)
So, what do we do? First, ramp down the speed as we approach the end of a path, so as to reduce the "static ooze" factor (tendency to ooze even when not pushing filament). Second, start retracting before the tool reaches the end of the path. The way it is now, it gets to the end of a path, stops, and retracts. During the stop/retract phase, the ooze happens, leaving unsightly blobs. A pre-retract option would let us specify the length before end-of-path to begin retracting. Once dialed in, the feed pressure + static ooze would produce a correct extrusion until end-of-path, at which point the filament would be rewound far enough that far less (ideally zero) further oozing would occur until after the retract/wipe/lift cycle is done.
This could also help with printed supports. If you've printed a lot of tall stuff, you may have run into a situation where the support gets knocked over after awhile. The nozzle running into a blob left at the end of a support path may be enough to shear the relatively weak support. No blob means no running into a blob, so perhaps this could enable us to print taller things with support, without having to finagle the settings forever to make it work without falling over.
The physics are pretty simple; we're just removing the cause of the blobbing before the blobbing has a chance to occur.
If you think this is a good idea and you'd like to see it implemented, it will help if you can post in that thread. More different people posting will send the message that people care about this enough that the developer should spend time on it.
The theory is this: Retraction causes blobbing because no matter how fast you retract (and you actually want to retract SLOW to reduce stringing), it can never be fast enough to defeat the hot end's tendency to ooze, unless you're printing thin layers at 20mm/sec. (And why have a Delta if that's all you're going to do?)
So, what do we do? First, ramp down the speed as we approach the end of a path, so as to reduce the "static ooze" factor (tendency to ooze even when not pushing filament). Second, start retracting before the tool reaches the end of the path. The way it is now, it gets to the end of a path, stops, and retracts. During the stop/retract phase, the ooze happens, leaving unsightly blobs. A pre-retract option would let us specify the length before end-of-path to begin retracting. Once dialed in, the feed pressure + static ooze would produce a correct extrusion until end-of-path, at which point the filament would be rewound far enough that far less (ideally zero) further oozing would occur until after the retract/wipe/lift cycle is done.
This could also help with printed supports. If you've printed a lot of tall stuff, you may have run into a situation where the support gets knocked over after awhile. The nozzle running into a blob left at the end of a support path may be enough to shear the relatively weak support. No blob means no running into a blob, so perhaps this could enable us to print taller things with support, without having to finagle the settings forever to make it work without falling over.
The physics are pretty simple; we're just removing the cause of the blobbing before the blobbing has a chance to occur.
If you think this is a good idea and you'd like to see it implemented, it will help if you can post in that thread. More different people posting will send the message that people care about this enough that the developer should spend time on it.
