What will happen if I set my retraction speed faster? Is there a reason why you would want it to be slower? How fast is too fast? It’s currently at 50mm/s. What happens if I just set it to 500mm/s? Will it cause any issues? Or will it just go as fast as it can? Is it bad to go really fast? I’m still getting some stringing issues (nothing crazy though) but I’m already retracting at 50mm/s and a distance of 6mm. I don’t want to go much farther because I’m afraid that the warm plastic will get too far up and cause issues. Thoughts? Suggestions?
It most likely won’t retract above a certain speed due to resistance of the filament path. When that happens, the drive gear will slip and grind the filament. If it makes a flat spot on the filament, it wont extrude as evenly as before. Too much filament dust will also cause problems such as clogging the drive teeth, reducing grip, and possibly causing jams. You can go higher than 50mm/s - I think some go 100mm/s or so. If you’re still seeing stringing, you may try lowering the temperature just a bit or increasing part fan speed (dependent on material type).
Large retraction distance will cause jams, particularly with all-metal hot ends. Pulling molten plastic into the cold zone is a baaaad idea. You always want the retraction seen at the hot end to be less than the length of the heat break, say under 2mm for most hot ends. Then add whatever hysteresis value you need for Bowden tube elasticity. Longer tube = more retraction distance. In a direct drive extruder, 1.5mm should be plenty unless it’s a really stretchy filament like TPU or nylon.
Speed is… eh. People differ. Slower speeds can perform better sometimes because, hypothetically, it lets the “pull” get down to the nozzle instead of just pulling the filament apart at the heat break. But you don’t want too slow. My experience is that 25mm/s is adequate in a direct-drive extruder. Faster can be really helpful to take up the slack in a Bowden tube. I run 60-70mm/s in my deltas.
If you set retraction ludicrously fast, the E axis acceleration settings will stop the extruder from actually reaching that speed, or the motor will skip. Skipping on retraction causes a big blob to get pushed out on reprise, unless of course the you skip on reprime too…
@Alan_Thomason I actually don’t have a part fan. It didn’t come with one. I do however have one ordered. When it gets here I’ll print off some kind of nozzel for it.
You want to retract quickly, but for pressure equalization purposes and to avoid extruder slipping/skipping, you want to unretract at a lower speed, closer to the rate that the plastic will be moving during your next printing move. I don’t think any slicers have implemented separate speeds for retract/unretract yet, but you can do it with firmware retraction in Marlin or Smoothie, or with a postprocessing script.
Cura 2.5 allows assymetric retract and reprime speeds. I like to use it to have a slow reprime since that seems to give me a more consistent first extrusion after a reprime.
@Whosa_whatsis@Mark_Walker Got any pictures of the difference? I don’t notice any issues with repriming on my non-Bowden bots, but they’re all Sailfish printers, so I wonder if the slow reprime is accomplishing the same thing as JKN advance somehow? Just a thought, no evidence to back that up.
@Ryan_Carlyle not at the moment. I’ll try to remember to do some later. I used it to solve a bit of under extrusion at the z-seam on some models, but it was on my delta as well. So I’m not sure I’ve used it on my sailfish printer.
Retraction settings, temperature and movement speed are two things to do with the amount of strings. Any slop/wiggle in the movement can fight the attempts to adjust movement to reduce stringing. I know movement speeds are not what you were asking about, but I figured I would just point that out. Good luck with your adjustments. Thanks for bringing up such a good discussion. I have to retune my string vs bridging balance myself after being a bit rusty, losing my settings and doing amfirmware upgrade.
Good point. If you can do your travel moves fast enough (with high enough acceleration), you don’t even need to retract. On the other hand, if your travel moves are slow enough, no amount of retraction will prevent ooze, because semi-liquid plastic is not immune to gravity.
I have my Ninjaflex settings using a high travel speed (7000 mm/min, so 117mm/s) and no retraction at all (not really worth it for TPU), and the few prints I’ve done in Ninjaflex / TPU have almost no stringing, so I suspect that a high travel speed makes quite a bit of difference.
You don’t need to go as much as you can, in this cases is enough - if print is clear. This option does not affect overall print time significantly. In most cases (on My printers) 4mm on 40mm/s is enough. Regarding cons of this issue: if retracting speed is to fast -you have a risk of cutting outward surface of filament by extruder gear and as result get the jam of filament. Because when you starting retract the filament, on start phase you have effect of inertia or kinetic mass or something similar with that. P.s. Sorry for my poor English))
If the surrounding filament is not hard yet, you may retract a crater out of your print if you retract too much. I had that pop up when playing around with settings.
Another reason for not going absolutely as fast as you can before (in the case of my Kossel) you strip the filament on the retract: if you go as fast as possible, then if you speed up the print by increasing the feed rate, the retracts will start to fail.
High retraction speed shouldn’t strip your filament. Unretract might, but slowing down your unretract will fix that. Even so, unretract should have minimal back-pressure, and at high speeds, motor skipping should be a more likely outcome than filament stripping. WRT, speed increases, if you set the E axis maximum feedrate to a speed that won’t fail, you don’t have to worry about that because the machine will self-limit.