printing round things without constant reversals of travel direction

[jens3 11]

I am printing pipe fittings for 6" pipe. There are three outside walls, three inside walls and a bit of infill. Nozzle size is 0.4 mm, line width is 0.4 mm, layer height is 0.4 mm, speed is 60 mm/sec except walls and first layer which run at 50% of that.

I would expect Cura to print the three walls in a continuous motion (with a step-over between walls of course). So for example printing the three outside walls, the three inside walls and then the infill. Problem is, absolutely nothing seems continuous about what Cura does. It will print a section of the wall, stop, reverse direction and print another section and so on.

This sort-of works with PLA but I am printing in PETG and am having blobs, stringing and burnt bits everywhere.

Yes, I know that PETG is prone to this and I have tried my best to fix it but my best is obviously not good enough 😞

So here is one issue I have noticed: Cura will print a section of wall. I have coasting turned on (default parameters) to take care of the filament that wants to ooze out as the head re-positions and that helps somewhat but I have noticed that when Cura does a reversal, there is still excessive material extruded right at the point of reversal (extra prime is turned off). The next time the head goes past that point there is contact with the nozzle and the extra material and I get stringing and blobs.

I am thinking that if I can somehow tell Cura to do a continuous circle motion without constant reversals I could possibly improve my prints by a large degree. I do not know the number of reversals in a single layer but I would not be surprised if it would add up between 20 and 30, not including the infill section.

I would also welcome suggestions on how to reduce the apparent extra filament feed right when a reversal occurres. This extra feed may happen without reversals when stopping at one point and continuing a bit further ... my eyeballs are not fast enough to catch that action though.

BTW, I am running at 240C for the extruder and am afraid that inter layer adhesion will suffer if I go lower. I am currently running at a flow rate of 90% - I have tried 85% but strength suffers, the pipe becomes even more porous and the stringing/blobbing isn't much (if at all) reduced.

[burtoogle 513]

Hello @jens3, I would like to help so please save the project file and attach to this thread so I can investigate. Thanks.

[jens3 11]

Thanks smartavionics - could you clarify what you mean by 'project file' please ?

I am using Cura 3.6 and with the model loaded I have chosen 'file, export' to generate a .3mf file. Hopefully that is what you are referring to ?

CCR10_15deg6in-mf.3mf

[burtoogle 513]

Hello @jens3. Actually, it's File->Save (not export). Exporting just includes the model. Saving, includes the settings and the model. I know it's not obvious, is it?

[jens3 11]

Here is the .3mf file generated by doing a save

CCR10_15deg6in-mf.3mf

[burtoogle 513]

H @jens3, thanks for the project file. OK, things you can do to improve this are:

 

1 - Enable the Optimise Wall Printing Order.

 

2 - Set a User Specified z-seam alignment with x/y values that position the seam where you want it.

 

3 - Set the Seam Corner preference to None.

 

4 - Set the Max Comb Distance With No Retract to 10.

 

5 - Reduce infill density, 70% is OTT for gyroid.

 

Hope this helps!

 

[jens3 11]

Thank you very much ! I am currently 8 hrs into a version of this print with a much reduced print speed of 30 mm/sec. It has another 16 hours to go 😞

It is printing a bit cleaner with less burnt bits (I am printing in white) but with just as many blobs. Stringing is reduced slightly.

The other change I made was to increase flow to 95% from 85% because 85% was just too porous. Oh, I also went from a 0.4 mm line width to 0.35 mm.

I am looking forward to trying the settings you recommended !

[jens3 11]

Started a new print job a while ago. I have about 2-3 mm down at the moment and I am seeing a LOT of improvement as far as stringing is concerned. I now see a couple or three reversals in a layer when it goes from inner wall to outer wall but there is no more of that frequent reversal issue. There seems to be no obvious improvement re brown bits in the print but I would imagine that with the stringing issue so improved, I will see less brown bits overall.

I reduced infill to 50%.

Of course I will not see the overall result until tomorrow (17 hrs estimated) but things are looking very promising - THANK YOU !

[jens3 11]

The print with the new parameters is fantastic! ZERO,NONE, NADA stringing ! The only minor problem occurs when a new layer is started and the filament laid down is not a continuous string but seems a bit interrupted. In the following pass the printhead nozzle will connect with the tops of the previous bumps and iron them causing bumps of white and burnt filament on the inside of the pipe within an inch of the z move to start the new layer.

This is easily sorted in the finishing stages so it isn't a big problem.

 

Again, thank you for your help!