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blawson

Cool head lift - why no retraction?

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I've run a few smaller ABS parts through our UM2 recently with cool head lift going and I've noticed the feeder is not retracting during the lift operation. I'm getting a little stringing because of it and sometimes the head oozes while it's out in midair.

I feel like a retraction makes sense here. Is there a reason this wouldn't work? Can the option be turned on somewhere?

 

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It works for me. But I'm not surprised you think it doesn't - even with retraction the nozzle still leaks a little bit - this is why printing with 2 nozzles doesn't work very well - the "off" nozzle never quite stops.

Anyway look at the code carefully - here is an example of a cool head lift - look at the end of the gcode. The G10 is the retraction, the G11 unretracts. G4 does the pause for 3.3 seconds.

 


;Small layer, adding delay of 3.319712
G10
G0 F9000 X83.07 Y90.88 Z31.90
G0 X103.07 Y90.88
G4 P3319
;LAYER:288
G0 X83.23 Y90.55 Z29.00
;TYPE:WALL-OUTER
G11

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I haven't consulted the gcode

 

Well let us know when you do. Then we can start figuring this out. For example if there are no G11 and G10's in there then you can send me or Daid the model and the cura settings and the cura version and someone else can confirm the bug and let you know if it is fixed in another version or a bug can be reported and Daid can fix it.

 

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if (liftHeadIfNeeded && extraTime > 0.0)
{
gcode.writeComment("Small layer, adding delay of %f", extraTime);
gcode.writeRetraction();
gcode.setZ(gcode.getPositionZ() + MM2INT(3.0));
gcode.writeMove(gcode.getPositionXY(), travelConfig.speed, 0);
gcode.writeMove(gcode.getPositionXY() - Point(-MM2INT(20.0), 0), travelConfig.speed, 0);
gcode.writeDelay(extraTime);
}

Pretty sure there is retraction in there

 

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I just grabbed something small and saved it to gcode and I do see a G10, followed by a jog straight up 3mm, a move +20mm in X, a G4 wait, then a move to the start of the next layer followed by an unretract.

I tried with a few options going:

with "allow retractions" unchecked there are no retractions (good!)

with combing enabled, retractions are included

with minimum distance between retractions set very high, it still retracts on head lift

with minimum extrusion between retractions set high, it skips retracting sometimes. Aha!

So it's the minimal extrusion setting interfering with the head lift retraction. I'm guessing the extrusion per layer on the parts I saw this on was pretty close to a multiple of the extrusion distance limit I had set so the skipped retractions were in sync with the head lifts. This could happen for any nonzero minimum extrusion length.

Basically, it's doing exactly what I told it to do, but I would like the behavior to be different. I want it to retract during the cool head lift even if that violates the other constraint. Perhaps it should be an option?

 

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We've had some problems with grinding on our UM2, some self-inflicted, and definitely material dependent. Limiting retractions made a big difference, but rerouting the filament was the best solution.

We built an enclosure for the machine that we use mostly with ABS that turned out to be preheating the filament, especially when the bed level is down around where the spool is. Eventually I put the printer on a cart and mounted the filament below it, not really a problem anymore.

Matterhackers black ABS was susceptible to it, Ultimaker black ABS seems less so (although it's proven harder to work with). PLA was an issue as well, but without the enclosure it was fine.

 

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... - even with retraction the nozzle still leaks a little bit - ...

 

The problem is, that it is not only a little bit. It's a lot of leaking.

Headlift01

Headlift02

 

I have looked into the gcode. There are some G10, G11 with G4 pxxx in the code.

The strange thing is, that on the very last head lift, before homeing, there is no leaking.

- PLA Ultimate blue

- 210°

- 40mm/s

- 0,08mm layer height

- Cura 14.06-RC5

How can I optimize my settings that there will be less leaking on head lift?

 

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You can change your retraction settings to retract faster and/or longer. It looks like you may not be retracting enough to drop the pressure in the nozzle.

You might want more fan cooling to freeze the filament quicker after its deposited.

I see some smearing on the overhanging corners of the body. I think this happens when the head heats layers below the printed layer and they get pushed around (and curl up) as it goes past. Along with more fan cooling, try increasing your layer time and increasing your minimum speed in cool. This will reduce the portion of time that the head spends over any given area.

Definitely ask in the "printing tips" section, I'd like to keep this thread on the topic of how Cura deals with retractions and cool lift.

Daid, can you weigh in?

 

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t looks like you may not be retracting enough to drop the pressure in the nozzle.

 

Yeah - what I was going to say. Also make sure retraction is enabled in Cura.

Change retraction distance from 4.5mm to 5.5mm. Retraction distance is not in Cura - it's on the printer itself. Or maybe more.

Why should Daid weigh in? He already did in a posting up above - maybe you missed it. #7.

That stringing you got shouldn't be too hard to remove. But if you want even better quality print 2 robots side by side at the same time. This helps a lot. That's how I did this one:

version 5f top half

 

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Why should Daid weigh in? He already did in a posting up above - maybe you missed it. #7.

 

Well he said the retraction is in there, but it isn't always, and I've identified the issue (bug?). the cool head lift retraction should be able to override the minimum extrusion per retraction.

I don't have a way to protect from stripping the filament while also not drooling on lifts.

 

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