Periodic Extruder Quality Issue

[sam]

Hi there,

Problem has recently cropped up of very poor extrusion quality but strangely this occurs at regular intervals every few layers. See photo...

Regular lines of poor quality build. The extruder is spitting material at regular intervals.

We had a nozzle blockage recently that created a very wispy part. Looked like a prop from the Mummy Returns! Withered and wispy. We cleared the blockage but we now have this persistence extruder issue.

See and example of pre and post blockage part...

Left, pre blockage. Right, post blockage.

While watching the printer the extruder seems to print a few good layers, then spits out a few bad layers. These layers don't bond, add lines of weakness through the part, and of course it looks sh*te too.

Poor infill layer.

It's not the slicer, i've tried parts using Sfact and Slic3r. Both equally affected. Dimensionally the parts are okay, so don't think its the XYZ axes. The extruder appears to be holding and feeding the filament okay, there's no white dust on the feed gear. Can't imagine it's a blockage again otherwise why would it come and go so regularly?

I'm stumped. Any advice please?

Cheers
Sam

[andrewsi]

Tried a different filament? (Just in case the filament itself has voids or has absorbed moisture or something?)

[sam]

Thanks Andy, same results with different filaments.

Turns out it was the filament tensioner in the end. We've tightened it up and back to good build quality again. Must have altered it taking the hot end in and out somehow.

All sorted now.
Cheers
Sam

[satoer]

Still weird a filament tensioner can cause such a repeating pattern.

[Dreide]

Indeed weird. On the other hand, if the tension is on the brink then small differences in filament diameter can make a huge difference in traction. The repeating pattern would then just be caused by a repeating pattern in the filament diameter which, I think, is not so far-fetched.