Cura limits retraction speed, don't know where

[Supramaker 0]

I tried to use a retraction tower for a new filament material using retraction speed as height modifier, and while doing so, I noticed that the maximum retraction speed at the top of the tower (80 mm/sec) never gets reached (I estimate it gets at 40 mm/sec max).

 

I checked my settings and could not find where this limit is set.

 

To verify, I did the same using Orcaslicer - there I went up to 100 mm/sec (just to test the limits). This means that the limit is not due to any firmware setting.

 

I need your help trying to identify where this limit is set in Cura 5.7. These are my pertinent settings:

 

I don't see where the limitation of filament speed comes from. The settings are similar in Orca.

Is there a json file or something with "buried" settings that I need to edit manually?

I can't remember if I ever had this limitation before (my retraction/prime speed settings are usually lower).

 

Thanks for your help, if any.

[Slashee_the_Cow 421]

The print speed/acceleration values have nothing to do with retraction - the retraction settings are in the Travel section.

 

There's a plugin available (just click Marketplace at the top right) called "AutoTowers Generator" with some preset towers (or with a teeny bit of hassle you can get it to make custom ones) which automates the process completely, all you have to do is pick the tower you want and save the gcode.

 

Also retraction going up to 100mm/s sounds sort of overkill to me - I realise my Ender-3 V3 SE is hardly a high end printer but its direct drive extruder maxes out at 60mm/s and even then I never go over 45mm/s.

[Supramaker 0]

 

I included all speed settings to avoid questions. I thought the retraction speed is related to *filament* movement, not travel.

 

I do have the Autotowers plugin, that was how I noticed the limitation.

 

8 hours ago, Slashee_the_Cow said:

Also retraction going up to 100mm/s sounds sort of overkill to me - I realise my Ender-3 V3 SE is hardly a high end printer but its direct drive extruder maxes out at 60mm/s and even then I never go over 45mm/s.

 

I was expecting that reaction. Yes, in general 80 mm/sec retraction is too high.

 

But I am not a general 🙂

 

My BMG geared extruder achieves 120 mm/s - but if repeating retractions in a row, I would risk slipping now and then.

 

I just found that in a specific case related to PETG and intricated models in a long Bowden setup the most effective way to avoid accumulation of oozed material in the travel path is to make the transition time between extrusions as short as possible. That means for travel movements: high jerk values (helps on short distances), high accelerations and high speed. The problem is, if you want a really clean printed part using PETG, and not to print it too slow, then fast travel movements are not enough in this case (direct drive might be different). The time spent while retracting also plays a role and it should be kept as short as possible - because even while retracting, material keeps flowing. Keeping a short time also implies *short* retraction lengths - the opposite as generally assumed. It is like paddling against the current in a river - you keep moving in the wrong direction, just a bit slower.

 

This is not just a theory. With this approach I am quite succesfull using PETG, but currently I have to use Orca for that because I have fast retractions then.

 

You should look at the nozzle after a print job using PETG is finished or just interrupting the job mid print - the filament flows and flows and flows by itself. How long would you have to retract to avoid that? Coping with this pressure is a challenge that demands non-conventional thinking. It makes no sense to retract longer if the the filament pressure overcompensates that movement at the same time.

 

I advice to open one's mind to information diverging from the "main stream", based on own experienced facts. I have gathered dozens of printed parts ("facts") and spent days (actually weeks) while playing with settings to avoid stringing. This is very specific to PETG in a long bowden system. Want more hassle? Use TPU. Or anything compressible.

 

But we are digressing. Still, no progress in my question: why is my retraction speed limited??

[Slashee_the_Cow 421]

Go to the Travel section of the settings:

The yellow is a warning, Cura's way of saying "are you sure you want to do this". Ignore it if you know what you're doing. Which you seem to.

 

And don't worry, I've printed plenty with PETG. When I'm manually purging the nozzle to insert it, I actually have to go into the printer's control panel and retract for it to stop coming (that or cool down the hot end). And then when I pull the excess away it stretches halfway across the room before it finally detaches from the nozzle.

 

I retract it at a longer distance than PLA (0.8mm for PLA, 1.5mm for PETG) but at the same speed (45mm/s). One thing you have to be careful about is that since it's a softer filament it's more liable to get chewed up by the extruder gears if you retract too often (which is why there's settings for a maximum number of retractions in the Travel section as well).

 

It's great you've found settings that work for you, considering that stringing is almost a given with PETG. And don't worry, I print with TPU a lot more than PETG. It's not quite as "oozy" as PETG, probably because it doesn't print quite as hot. But given that you can stretch it just coming off the spool, retracting is basically an exercise in futility considering you're just more likely to stretch the part between the extruder and nozzle than you are to pull it back. I could try setting the retraction distance pretty high (I do 2mm, which is sorta high for a direct drive, but I could always go higher) and as fast as possible in the hopes of "snapping" the filament but it'd probably leave more than enough to string until it starts extruding again.

 

I would like to warn you about the travel jerk though: it's pretty high (duh). The problem with that is if you have a model which isn't perfectly stable it's liable to wobble a bit and if you start extruding pretty much immediately afterwards it might do it in the wrong spot. You also run the risk of the build plate (or print head, depending on what type of printer you have) slipping a step or two resulting in layer shift.

[Supramaker 0]

Thank you for guiding me to the retraction settings 🙂

There is no other place to do it...

 

2 hours ago, Slashee_the_Cow said:

You also run the risk of the build plate (or print head, depending on what type of printer you have) slipping a step or two resulting in layer shift.

 

Yes I know this problem, it has happened to me. That is why I am working on an automatic calibration of stepper skipping, that is, finding the limits to avoid layer shifting. But in most cases, my belt was not tightened strong enough, so I got a belt tension gauge and since then no more layer shifting. I have also implemented a detection of stepper skips (using RRF) based on measurement of motor voltage/current.

 

At this very moment I am printing using RetractContinue, which is a bless, but is causing underextrusion after a number of retractions... still investigating.

 

 

[Supramaker 0]

After many changes and experiments, I can confirm that higher retraction speeds are possible.

I cannot identify the exact step that solved the problem.

This issue can be regarded as closed.