Blobs all over the print surface

As the attached image shows, the outer skin of my prints is very blobby. It is caused by large amounts of PLA being extruded whenever a suck-then-prime step occurs, which is typically at the beginning of a perimeter.

I’m pretty sure the extruder is running correctly as the prints are not too thin or thick anywhere else. I’ve tried retraction settings from 1mm to 5mm and use 15mm/s retraction speed. The hot end is at 200 degrees, although I’ve tried it lower and higher without improvement.

It hasn’t always done this and I don’t think I’ve changed anything significant in the software configuration, which makes me think it is a hardware problem.

Yesterday I took the hot end apart to put in some tape to stop the PLA leaking problem, but the blob problem is just the same afterwards.

In case it’s relevant, I use Kisslicer and it is apparently sequencing the retractions properly, but the prime step always oozes too much plastic. I’ve asked it to start perimeters in random locations, otherwise the blobs build up on top of each other and cause other problems. I’m switching to inside-out perimeters, which should improve the aesthetics of the print, but it will still be a problem for thin / small areas.

When you start a new layer, there are a couple things that determine where that layer starts. You can either have the layer start exactly the same equivelent spot on the perimiter going up in a line, which tends to leave a long zipper like track up the side of the part, you can have it start in random positions such as you have there, which starts it in a different part on the outer perimiter of the part, or you can tell it to start the layer on inner perimiters, whiich moves that distortion to the inside of the part. you can also tune your retraction settings to pull back a bit more fillament before going to start that layer. But the easiest trick is to just set it to do the exterior perimiter last. With single layer thick prints that still doesn’t help, but it tends to make almost everything else look much better.

Thanks @piercet. Spreading the seams around and starting inside out definitely improves things.

Retraction certainly used to work better for me, so I think something has got loose or out of alignment.

It could be nozzle tip wear. As the nozzle gets used it slowly bores itself larger, Over several years of heavy printing, or a few months of printing with something abrasive like woodfill your 0.50mm nozzle can end up as effectivly a 0.55mm nozzle and cause things that appear to be over extrusion and under retraction. Aside from that, the only physical modifiers would be wear on the gears, the idler arm tensioners coming loose, debris in the hobbed bolt chamber, or possibly a bearing going bad, particularily the one in the idler arm itself, though that is rare anymore with the sealed bearings.

Other possibilities can include ageing motors not operating quite as efficiently or thermistors that are not quite as accurate as they were and your temperatures could be off a few degrees.