Crazy extraneous travels

[LindsayPatten 1]

I've got a part I've been having a hard time getting to print on my Creality K1 Max until I reduced printing speed to half of normal.  While it was printing the bottom layers it would travel back and forth so much that the printer would lose its origin and start printing in an offset position when printed at normal speed.

At half speed it would print okay, and in fact once it was through the bottom layers I could raise the speed back to normal and it would print the middle layers okay.

While watching it it seemed to me that it was jumping around the print an awful lot more than seemed necessary so I looked at the preview of the bottom layers in Cura and saw that there are what appear to be a large number of unnecessary travels most of the way across the print and back, here's layer 2:

If I step through the animation there are actually a ton more unnecessary travels that don't show in the image because they trace the same paths repeatedly and/or trace the wall outline repeatedly.

Any idea why it is jumping around so much?  It is Cura 5.8.0.

CK1MAX_Cowl60x10PlusTol.3mf

[Slashee_the_Cow 410]

Most new Creality printers these days can print and accelerate far faster than is a good idea, let alone necessary. I'm pretty sure it's part of a pissing contest with other Chinese manufacturers to print a Benchy the fastest. You should turn down the maximum acceleration in the printer's control panel, because sometimes it ignores what's in the gcode. I set my E3V3SE to max out at 1000mm/s² (maxes at 4000mm/s² - I think - the Creality website says 2500mm/s², the manual says 5000mm/s², the return from an M503 command says 4000mm/s², but the setting on the control panel goes up to 5000). Don't forget Slashee's Golden Rule: Slow print > bad print.

 

Now as for your travels... I guessed it might have something to do with the angle the lines were at. My suspicions were confirmed when I rotated it on the build plate and made it worse:

So then upon a hunch I rotated it so that it's parallel to the X axis on the build plate, so the lines went at 45 degree angles:

(And just to be clear, by "parallel to the X axis" I mean this)

I think the problem is that with the lines at extreme angles it's generating a lot of tiny "islands" of skin. So either rotate your object on the build plate or play with the Top/Bottom > Top/Bottom Line Directions setting - to replicate the default you need two angles offset by 90 degrees, like [45,-45] or [45,135].

[LindsayPatten 1]

Thanks for the reply.

In Cura the default accelerations all seem to be 500 already.  I can't find anything on how to set max acceleration on the K1 Max itself.

Unfortunately, the main part is a helical blade that twists over its length so aligned at the bottom means not aligned at the top, although I guess I could use a support blocker thingamajig to deal with that.

Isn't it a bug though for the print head to go to the far end of the print do nothing and then come back?

(Sorry if I'm not very coherent, I'm being rushed here)

[Slashee_the_Cow 410]

It's not doing nothing each time... it's doing a little each time. It will travel a lot less (and take much more direct routes) if you set Travel > Combing Mode to Not on Outer Surface instead of Not in Skin.

For example, as oriented in your project file:

It decides that a good place to start doing skin from is here:

Then it moves down and does this little bit:

Then it moves back home:

Then it hugs the outer wall so it doesn't have to retract to move and do this little bit:

Then it just moves to the side a little to do the mirror of that first little island it did:

Then it does a retract move along the inner wall to do this tiny spot:

Then it actually does something sensible and does a short retract move so it can do the skin wall for that section:

Skip ahead a bit and it's gone back "home":

Then it goes down a bit to do the tiny bit at the end of that side and do a tiny bit to mirror the other side:

Skip ahead a bit and it's just finished the skin wall around the area on the right:

Does a short travel and then does the first line in that section:

Decides to take a trip back home:

Travels around the edge (so you can't see the travel as it's already been that way several times) and does this line:

Heads back home directly:

Does another direct travel move straight back and does the next line:

Then does the smart thing and does the next line:

Then heads directly home:

Then heads straight back and does the next line:

Smart thing (next line):

Direct move back home:

Then a direct move back to the start of the next line and does that line:

Repeat this several more times. So why does it go back home instead of just moving to the next line?

1. Look at the difference in the distance between the line ends at the top the ones at the bottom. They're so far apart it doesn't think it can do a short move between them which avoids travelling in skin. That's why changing the combing setting will make it not do that: since the second layer is now fair game, it takes whatever routes it figures are quickest while avoiding walls.
2. Due to the tight spot (in my next picture) it can't find a route which avoids travelling through the skin, so it just does a direct travel on the shortest possible route - if it wasn't for that tight spot it would be avoiding the walls.
3. There are approximately a bazillion routes it can take and it doesn't have time to calculate all of them so it just does something easy and familiar.

It also doesn't help that when you've got tight spots like these:

And hard angles like this:

And bits cut off entirely like this:

If the line angles aren't ideal it also has to do a lot of tiny little spots to fill in gaps due to the line transitions (where it changes the number of lines as the width of something changes). You could try turning on Experimental > Infill Travel Optimization but I found it didn't make much difference.

 

So it's not really a bug. Just a perfect combination of poor circumstances with the angle of the lines being so steep relative to the section they're in combined with that tight bit which it can't comb through. Which makes my answer: if you can't orient it on the plate so the lines fall in more favourable directions (or just manually set the lines to a good angle), change your combing setting to Not on Outer Surface so everything but the top and bottom layers are fair game.

 

Hopefully that hasn't put you to sleep 🙂