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My Kossel Mini printer was working well. Recently I made some changes including replacing the nozzle and throat, adding a silicone heater cover. Now it has the problem of first layer adhesion.

The perimeter sticks well but the infill line swells upward in the middle, while start and end has no problem.

In my experience the adhesion problem only occurs at corner but never in the middle. So I don't know what configuration needs to be changed to fix it.

Delta calibration has been done before the print. PVP glue was used on the bed.

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  • $\begingroup$ that's not a swell up, that's just really poor adhesion. Have you ever cleaned your bed with alcohol or Isopropanol? if not, try it. ; The silicone around a heater block is called a "silicone sock" $\endgroup$ – Trish Jan 18 '20 at 19:33
  • $\begingroup$ @Trish: Are you sure? It looks like it could be a mechanical problem with the delta configuration. $\endgroup$ – R.. GitHub STOP HELPING ICE Jan 18 '20 at 21:14
  • $\begingroup$ @R..GitHubSTOPHELPINGICE It's an unheated glass bed. It might also be that he swapped gluestick brand. not all sticks are equal! $\endgroup$ – Trish Jan 18 '20 at 21:45
  • $\begingroup$ @Trish I'll try to clean the bed and also try another gluestick. There is one think I don't understand: PLA shrinks when it cools down. The shrinking won't make the middle of infill move upward. It looks like that I need to double check the delta configuration as well though I don't think I had changed it. $\endgroup$ – aleung Jan 19 '20 at 6:19
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Had tried below and didn't work:

  • Clean the bed
  • Use a brand new glue stick
  • Verify delta configuration and make sure z-plane is flat and parallel to bed
  • Adjust z height to minimize the distance between nozzle and bed when z=0
  • Increase first layer extrude width

Printed again and watched carefully, then found that it was pull up because the printed PLA slice shrank. I realized that the problem was related to my change on the fan duct. Before, the fan blowed directly to the tip of nozzle; after changed it blows around.

Tried to turn off the fan on first layer, the problem was solved.

I suspect that the fan duct change made the extruded material not cooling down immediately. It shrank when the air blew on it. I need further test to verify it.

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    $\begingroup$ Of course! Cooling the first layer is a classic that results in failed prints... The effect is amplified by your bed being unheated glass. Turn cooling fan to turn on on layer 2. $\endgroup$ – Trish Jan 19 '20 at 18:17

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