Retraction / bubbles

Printing in PLA, I’ve noticed that shortly after a retraction (a few seconds later), I hear a little air bubble pop/snap sound. It leaves a tiny litle pit on the print. The sound and pit are very similar to the problem you might face using damp filament. this though is totally dry, and it only happens shortly after retractions. Has anyone else noticed retractions introducing air into the nozzle? If so, any tips?

This is a close-up detail. These are .25mm layers.

I guess your retraction length is set too high. Then air will come between the molten filament in the heat chamber and the solid section you are retracting. During unretract, the air gets trapped as bubbles in the molten area and finally into your print.
With pla you don’t need much retracting. Values between 0.7 and max 1.5mm should be enough.

Thank you Sebastian,

When I was using high retraction, the problem was much worse. Now, I am using 1.25mm, but even at that retraction I am getting the pits. Is it still possible this is too high do you think?


I would print a test part completely without retraction just to be sure it’s due to retraction. If it is, I would lower the retraction distance. Also check your retraction speed, maybe it’s too high?