Safe UM2 Retraction settings?

[txesc 1]

tl;dr - my retraction settings are a lot higher than recommended. Is that going to cause problems down the line?

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New Ultimaker 2 user here.

Really impressed with how quickly the machine was up and running, the speed and the quality of prints.

However, I'm quite picky and have never used a bowden set-up before.

I've been trying to eradicate as much as possible the seam created by the pauses in a retraction move repeated on every layer (does Cura have a 'randomise start points' option like slic3r?).

The material is the roll of PLA that comes with the machine, printing between 40 and 60mm/s.

So far, I've got the seam down to be fairly imperceptible and I'm pretty happy with it. I've gone to 6.00mm @ 45mm/sec and added a 0.1mm Z-lift (hop), which is fine for a simple model with only two regular retractions per layer but I'm a little worried that with anything more complex that this will cause jamming.

What's everyone's experiences with more extreme retraction settings? Do you need them? Are they more trouble than they're worth?

Have you found you needed to change the settings a lot per model or does one setting generally sort them all?

 

[gr5 2,172]

I was at 5.5mm retraction for a while until I seated my bowden more firmly - it used to go up and down with each retraction. Now that it's firmly tight I am happier at 4.5mm retraction. If you retract too much air will get into the nozzle. Which is bad.

Regarding seams and bumps. You can reduce these by printing slower. I find 35mm/sec is slow enough for excellent quality or 20mm/sec for best possible quality. This results in a constant extrusion speed around corners and such which helps greatly to eliminate under and over extrusion on slow down/speed up.

35mm/sec should eliminate your Z seam.

I've never had to use the Z hop. It's really more for delta printers I think where all 3 steppers are moving on every move anyway.

You can also reduce your Z seam by increasing Z axis acceleration. I have only messed with this on the UM Original but was able to get my Z movement from a brief sound to a click it's now so fast. Just by doubling the acceleration (didn't touch Z velocity). I haven't messed with Z acceleration on my UM2 but it sounds much slower than my UM Original so I suspect you can safely double it.

 

[txesc 1]

Thanks gr5.

Good shout on the bowden seal. Mine is currently moving, but all i can do is just push it down a little more, the blue shoe doesn't seem to be doing much, each time i push it down it just pops back up again. How did you seat it better?

The Z axis acceleration - is that 'Max speed Z' in the maintenance menu on the machine? It's currently set to 40mm/s, which seems fast enough. How fast does the UM go?

 

[pm_dude 27]

You can find some bowden clip models on youmagine.com. I couldnt find the one with a tirap I was looking for but I saw some version out there... Worst case you can do one yourself.

[txesc 1]

Thanks pm_dude. There's a few possibilities on there. All with slightly different wording making them fun to track down. Lot's of great ideas.

What's the aim of the clip - ideally, does it restrict all movement or does there need to be a bit of give?

[IRobertI 520]

Ideally the bowden should not move at all.

 

[pm_dude 27]

I'm thinking to make one that will also support the bowden a bit above the print head. Mine is starting to bend on the side a little (far from being a problem right now... ).

Same for the back. I saw a clip to hold it straight above the feeder.

 

[eldrick 65]

Z-hop is exactly what you need when printing PLA with overhangs that tend to curl upward. It allows you to keep printing without knocking over the piece and ruining it. I use .08 as a value.

 

[txesc 1]

pm_dude were you thinking along the lines of something like this -

https://www.youmagine.com/designs/printhead-bowdenfix-um2#!design-information

or this

https://www.youmagine.com/designs/bowdentube-holder-vor-um2#!design-documents ?

Personally I'm hoping one of these will do the trick -

https://www.youmagine.com/designs/bowden-locking-clamp-clip#!design-documents

I haven't touched the the travel speed yet, but was tempted to take it to 200 or 250mm/s. I use 150 on my mendel style printers, but as to whether the actual speeds ever touch the speeds in the gcode is another question...

 

[pm_dude 27]

Tx.esc No I'm thinking about something that will allow to unclog the nozzle easily and without needing to loosen screws or throw away tywraps. I'll give an update on that as soon as I have 10 min on my pc

Travel speed at 200mm/s is great but I dont know why on my printer even at 100mm/s I get some holes drawn on the bed that seems to lift because the head is moving fast and starting to extrude right away... The first inner shell after the skit is done seems to perform a very small pause after the travel and before extruding but the following inner shell will not do that and sometimes it cause the begining of that new shell to lift from the bed. This happen only on the initial layer and is quite annoying.

[txesc 1]

100mm/s travel? Is it in the same places each time or doesn't it matter? Are you using any skirting loops?

[pm_dude 27]

Yes I do 3 loops of skirt and yes most of the time its always at the same place since the print always start the same way.

Here is a TERRIBLE image to demonstrate this using a screen shot on my phone and finger painted on top of it while in the park lol

so when the print starts (green dot), does the first contour its fine. Then, when it moved to the first inner part to print the contour it doesnt stop at all like when doing the previous and sometimes the string stay attached to the nozzel and lift from the bed.

 

[gr5 2,172]

On the UM2 you don't need any clips to tighten the bowden. Just loosen the 4 long thumb screws about 5mm, then with no clip, push down on bowden and then while still pushing down lift the bowden-holder-ring thing. Then tighten the 4 thumbscrews. Don't tighten the bowden too much or it will be pushing down hard on the white teflon piece (along with the spring). That teflon piece can deform after many weeks of printing at high temps.

On another note:

I almost always use brim. It's very easy to peel off. I only use skirt for very small parts. Smaller than 25mm across.

And regarding Z acceleration - no - it's not zmax. It has the letter A and Z in it. Like "Z Accel" maybe? "ZA"? Not sure. Gotta go out now. Maybe it's not in the UM2 motion menu but I think it is.

 

[pm_dude 27]

On the UM2 you don't need any clips to tighten the bowden. Just loosen the 4 long thumb screws about 5mm, then with no clip, push down on bowden and then while still pushing down lift the bowden-holder-ring thing

Ok I'll have to try that.

Brim could work too but since its doing the inner shell first it would still not touch the brim and could lift. I'll have to try

 

[txesc 1]

So do the Bowden tube and the Teflon piece on the hotend need to touch but not exert force?

[pm_dude 27]

Ok so I got some time to do the bowden clip and a guide for the tube itself.

https://www.youmagine.com/designs/um2-bowden-clip-and-guide

In fact the guide doesnt really do much but it supports the bowden tube a little better and makes it perfectly straight. The clip fill the 2mm gab between the white bowden clip and the top of the head.

gr5,

I dont really understand how we can remove the need for the clip seing the 2mm gab I see moving up and down when having big retraction settings.

also I was wondering if the spacing between the white teflon piece and the nozzle was normal. I have the impression it wasnt there before and may have appeared when un clogging some wood fill...

 

[txesc 1]

pm_dude mine looks like that too. but I've been fighting a number of extrusion issues for the past couple of days, so I don't believe my machine is a shining example yet.

 

[eldrick 65]

Here's another solution - bowden clips in different heights:

https://www.youmagine.com/designs/ultimaker-2-bowden-clips%C2%A0/

 

[IRobertI 520]

@pm_dude: The gap is supposed to be there. It's even mentioned specifically on page 56 in the assembly manual. The gap should be at least 1mm.

 

[pm_dude 27]

Yes in fact I posted in my design your name and link to your clip as it was my base for the bowdeb guide .

I started from yours and found I needed a 2mm clip to remove any gap

[pm_dude 27]

@pm_dude: The gap is supposed to be there. It's even mentioned specifically on page 56 in the assembly manual. The gap should be at least 1mm.

 

But doesnt that cause an offset in the retraction?

[IRobertI 520]

Why would it? The teflon piece is stationary, in essence an extension of the bowden tube, so I don't see how it would affect retraction.

 

[pm_dude 27]

Ok. Then why do I see many posts about holding thhe bowden clip thighter even with tywraps? I might have just not understood the problem properly but I was under the impression that the lift of the tube during retraction was not really desired.

EDIT: Oh wait I just understood you are talking about the gab I asked about between the teflon and the nozzle. haha... Thanks Robert

[gr5 2,172]

I dont really understand how we can remove the need for the clip seing the 2mm gab I see moving up and down when having big retraction settings.

 

Mine also moved up and down when I first got it and for the first month or so. Then I got a clog and had to take the head apart. When I put it together again I tightened the bowden before tightening the 4 thumb screws. As I tightened the 4 thumb screws the bowden-holder thing got higher and higher until it was all the way up and now I have the little clip on there but it does nothing.

So loosen the 4 screws quite a bit (maybe 3mm?) then shove the bowden FURTHER in. Then tighten the 4 screws. You won't need any clips or anything and it will all be solid and not move.

 

[valkyriedynamics 0]

the problem i think i had was the material is retracting getting binded up....... in cura disable retraction and turn heat to 240c