Weird bumps cylindrical hole


Not quite sure what's happening here. I printed it as a single ball and had this effect. I thought it might be a cooling issue so I printed 4 at once but the issue still occurred. If I size the ball up, the problem reduces.

Note that the hole is supposed to be a cylinder.

Photo of four balls exhibiting bumps around a cyclindrical through hole


Posted 2016-10-22T15:25:37.193

Reputation: 407

Do you have a gcode viewer that lets you see each layer, retractions, etc.? You might get a clue from that. And are the sides of the balls printed normally, or do you see distortion in the side wall under each tiny ball? – Fred Hamilton – 2016-10-22T21:12:34.390

Can you post the original STL, and in addition the slicing tool you're using (and any pertinent parameters you set in that tool)? – Carl Witthoft – 2016-10-24T12:45:38.300



It looks like possibly a combination of too high of extruder temperature and poor retraction.

  1. First, try reducing your extruder temperature. PLA ideal extruder temps range from about 185C to 225C; depending on purity, quality, and climate. This can help prevent additional oozing and clogging. If your extruder clogs easily, you probably have too high of temperature.
  2. After you've verified you have correct extrusion temperature. Try finding/adjusting retraction settings in your preferred slicing engine. Here's a good troubleshoot page from Simplify3D's website.


Posted 2016-10-22T15:25:37.193

Reputation: 6 144

The blobs in the picture look very "watery", which indeed indicate a far too high extrusion temperature. I guess the round drop shape comes from a z-lift movement on retraction, which is usually very useful to avoid nozzle collision during travel moves. On a side note: using a too low nozzle temperature can also cause clogs. If you have no idea where to start, I would try 205-210C for typical PLA, and take it from there. – Tormod Haugene – 2016-11-23T21:37:10.827


In order to exclude a cooling issue, you could try printing a larger object alongside the spheres. Something that has a constant cross-section and is at least as high as the spheres.

I have had issues when printing objects with a sharp tip, even printing 8 at once the total amount printed on the top layers was not enough to let the material cool before the next layer.


Posted 2016-10-22T15:25:37.193

Reputation: 61


It looks like it is trying to fill in what might be small gaps and is putting blobs down because the gaps to too small of a detail to accurately fill.


Posted 2016-10-22T15:25:37.193

Reputation: 417

1This is quite short for an answer, and it doesn't do what an answer is supposed to do: how would you solve this problem. Change the design? Slicer settings? – Tom van der Zanden – 2016-10-23T07:14:46.233

@TomvanderZanden it doesn't look like the OP specified their slicing engine. So, it might be a bit premature to suggest slicing settings. – tbm0115 – 2016-10-24T14:14:42.927