Gaps in print Taz 6

I’m a newbie Taz 6 owner, and am trying to print some mould parts, which don’t need to be ultra detailed, so I changed nozzle to 0.8mm. I’m now getting these strange gaps in the print, which was also happening with the 0.5 nozzle ( though not as extreme!)
Anyone seen this issue? Assuming it’s some hidden Cura setting?
Thanks in advance, Sebastien

Could be an issue with the STL. Can you share it?

My initial guess would be that it’s a thin wall. There is a setting for “Print thin walls” you can check.

Hi Wrathernaut, thanks for the reply…I tried the ‘Print thin walls’ option with no difference. It’s a very strange thing! I attach another photo that shows how badly it’s printing… You can see the feeder wheel pull back (retract?) at the points where the prints are bad, so I’ve tried playing about with the retraction settings and the flow, but no change. It’s a brand new nozzle too.
I have loads of other printers working just fine on my Print farm, so don’t think it’s the STL.
Grateful for any other suggestions.
Cheers Seb

Can you share the STL file and what version of Cura are you using?

The linear advance/K-value settings might be stacking together, so it’s stopping flow too soon.

A screenshot of the layer view of the file from Cura might help determine what’s going on also.

Is it possible that you have the slicer setting for a toolhead with a 0.5mm nozzle versus your newly installed 0.8mm nozzle?

Nozzle size merely affects the recommended layer/width sizes, with Cura highlighting values that aren’t a good match in the slicer. At .5 or .8mm, you still need to extrude the same volume of material through it to get a specified line width and height.

If you’d gone from a .8mm profile to a .5mm profile, it could lead to underextrusion, if your profile was tuned to maximize the volumetric output of a bigger nozzle which would lead to less pressure and less work for the extruder. If this were the case though, it would almost certainly lead to stripped filament and stopping the print fairly quickly, not continuous locations of underextrusion like is seen here.

Don’t the E-steps come into play going from a 0.5mm toolhead profile to a 0.8mm one?

E-Steps are related to the stepper and mechanical mechanism driving the filament, and in an ideal world would be unrelated to the nozzle size. However, given that at least with the older toolheads the E-Steps varied from toolhead to toolhead (even with identical nozzle sizes), I’ve tested each of my toolheads and labeled them with the E-Steps.

In practice, they’re generally close enough that while you’ll get noticible quality issues if you don’t reset the E-Steps, it shouldn’t look like the photo provided.

Nozzle size doesn’t affect the amount of filament needed to produce a given line of filament.

What would make a difference, is if you were pushing your motor/drive system to the max possible with a low-resistance, open .8mm nozzle, then moved to a more restrictive .5mm nozzle, you might lose steps by the motor being unable to push that hard, or the gears grinding away at the filament and not pushing.

At some point, your gears could wear down and effectively make them a lower gear ratio when engaging the filament, but that’s for weak gears pushing a lot of abrasive filament, and can generally be ignored.