Lumpy strings on first layer

[dparrish]

Hi, I've got a Cocoon Create from Aldi (Australia) which appears to be a clone of the Wanhao Duplicator I3.

I've spent the last week printing almost a kilo's worth of PLA items but now I'm noticing a lumpy stringing in the first layer of the print.

This only happens in an area near (but not exactly) the middle of the bed, the rest of the first layer looks fine to me.

I've spend time cleaning the surface with alcohol and then re-levelled it.

The lumpy strings in this area feel quite rough. The lumpiness disappears after the first layer so it doesn't really impact the print, but the bottom surface isn't smooth.

Does anyone have any tips or suggestions for me? Picture (mid-print) attached.

[Alibert]

Your nozzle is a bit too close to the bed. When extruding, the plastic curls to the sideof the tip making the rough surface. After the first layer, the correct height increase conforms to the amount of plastic that is extruded making nice layers.

If you want to improve the first layer you will need to re-level your bed. However, when the z0 position is set too high, you may get poorer adhesion to the bed resutling in warp/lift. So, re-level but not too much.

[3dex ltd]

Alibert explained it really well above!

I think it is most likely to be your nozzle height in relation to the bed. It's very easy to go too far in the other direction though and the result is very poor bed adhesion and poor 1st layer adhesion (to the rest of the print)

Hope this helps though

[dparrish]

Thanks very much for the replies, I appreciate the help. Would that explain the repeated sections of lines through the first layer? I would have expected that if the nozzle was too close to the bed then it would happen everywhere (or on a corner where the height is different).

[LambdaFF]

Thanks very much for the replies, I appreciate the help. Would that explain the repeated sections of lines through the first layer? I would have expected that if the nozzle was too close to the bed then it would happen everywhere (or on a corner where the height is different).

No, you see, this is a creeping defect.
On the 1st line, you have some overflow, but since it is a % of a small output, almot negligible. But then on the second line you cumulate the defect of the 1st line and the second. On the 3rd line you cumulate again... Also, it is indeed reinforced or dampened depending on local variations / defects of your build plate.