Suggestions for clean small print

[dkightley]

I've been struggling with one set of small truss girders I'm trying to print in PLA with a 0.4mm nozzle. Here's a close-up of one of five that are together in one print:

You'll see by the scale on the bed, this girder is just under 2cm long, and a typical member is around 0.9mm x 0.9mm in section.

Try as I may, I'm finding it difficult to tune the settings to get a clean print. I've tried varying tweaks to retraction distance, lift, & speed, and differing coasting distances and reduced temperatures down from my normal 230 down to 210. Here's a typical print that I've stopped early to illustrate what I'm getting:

The crazy zig-zag is support, but what I mean is the mass of very tiny strands running back and forth between the sides, and between the sides and the support.

This print was done with two processes; one for the majority of the bottom cross-members at 230C...to ensure the cross-members form correctly, and a second process with a temperature of 215C for what would be the vertical diagonal members...which is where the stringing occurs. I've run this with:
Retraction: 2.9mm Restart: 0 Vertical lift: 0.2mm Speed: 1800mm/min Coasting: 1.5mm

I've tried retraction at stages up to 5mm, vertical lift up to 1.5mm and coasting up to 1.9mm (although with a potential extrusion distance as low as 2mm a go, I daren't try a greater value. Putting in an Extra restart of 0.2mm stops the printing dead!

Any suggestions on shortcutting my testing?? Attached is what I think was the factory file for the print in the photo.

[Rebekah_harper]

hiya,

I would use a smaller nozzle.

check out AVN Swiss for a 0.2mm they work perfectly.

other than that, slow down the print massively. and start again but with no retraction or anything and see how it goes then just add a little retraction but no wipe.

[dkightley]

I have thought of that...but I've been able to print other parts with similarly small members with a 0.4mm nozzle.

I think most of my problem is the fact I'm using support material....and ooze control doesn't appear to work on support. I think I'm going to resort to manual support for the upper horizontals and try printing again with the same profile settings....and then file tune from there.

[Rebekah_harper]

use the sectional view and check how the layers are.

you might get away without support.

I usually do a sectional view to see if there are any layers that are beyond the previous layer's perimiter.

for small parts i keep retraction to a minimum and have nothing else that deals with filament handling.

[dkightley]

use the sectional view and check how the layers are.

you might get away without support.

The only place this part needed any support is for the overhanging ends of the top horizontals. I've since extended the ends to incorporate a support as part of the model that I can remove when printed, so I can do away with slicer generated support. I realised that using support increases drastically the stringing...see this thread: viewtopic.php?f=9&t=3671

I've considered going to a 0.2mm nozzle, but I'm doing a lot of printing at present at 0.4mm and the hassle of changing nozzles and realigning the bed is putting me off. Apart from that, I did try a 0.2mm nozzle, but it clogged almost straight away...which I think was an issue with burnt deposits being dislodged...and I have to admit to being apprehensive about disturbing the print head too often!

I'll probably have to go down to .2mm for some smaller section girders I have coming up in the next few weeks, but I'm running a few test prints at the moment to see if I can minimise the stringing with what I have now.

[dkightley]

Here's the best I can get at the moment with a 0.4mm nozzle:

5.5mm retraction, no extra restart, 0.2mm lift and retraction set at an impossible 10000mm/min; 0.5mm coasting.

This will do for this component, as its within the realms of being cleaned up with a scalpel.

And yes...that is a pound coin its sitting on!

[dkightley]

....and the hassle of changing nozzles and realigning the bed is putting me off.

I shouldn't had said that!!!

The very next print after printing the part in the above photo failed to print with the filament jammed firmly in the hot end of the print head. On complete disassembly, I found the PTFE liner had given up and broken in two, with half of it welding itself to the filament. Fortunately, I have some spare tubes (unlined), so one went straight in.

Now I have a bed to get tuned right...and more work on the profile settings!!!