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Top layer missing/bad from print, what could cause this?

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Hey guys,

The top layer of models seems to be incomplete. As per below pic, in stepped models walls are fine, just the top layers. Any ideas?


Sorry can't embed pic as on iPhone. Mods if this is in wrong section please can you move.

It's so frustrating, can't produce any prints properly, and have to scrap the ones above too now! Any help much appreciated.


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1) Did you look at the part in Cura layer view first? Make sure cura thinks it is *supposed* to fill in the tops.

There are lots of reasons why it might not fill in the top. But here's my second most likely reason:

2) The photo sure looks like underextruded infill although the walls look okay. Do you:

2a) ...have a different infill speed than shell speed?

2b) What is your print speed, nozzle temperature and layer thickness? These 3 values combine in a curve such that if you are above the curve it will underextrude badly:



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Thanks fore reply gr5.

1. The layer view in cura showed it as being there.

2. the walls are perfect, i'll get a better photo tonight.

2a. I do have infill set to 130%, but the infill was coming out fine, the missing layers are the top/shell.

2b. Print speed was (i think but have to confirm on gcode), 80mm/s, 0.2 resolution, 212 nozzle temp.

Taking a look at that graph, i'd expect to see underextruded infill, but its not. Its the slower layer that is (possibly) underextruded. Take with the the fact the walls are absolutely fine, its very odd. The top layer of the wall is also showing the same problem (although on much small scale).


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Yea its two parts its happened on now. the walls were printed after the main piece, and they came out fine so struggling with the concept of a blocked nozzle. Will atomic it just incase though.

I also printed some nano props yesterday, and had no such problems. However these don't really have a 'top' to them, so maybe thats why the problem didn't manifest itself with those.


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Oh right, didn't notice at first that some walls were going higher than some internediary "top" surfaces.

Have you checked what anon4321 said? the solid infill top was checked in your expert settings? It should, if you say that it is visible in the layer view, but just to be sure.

Your printer is a modified/copycat UMO?


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212C, .2mm layer, .4mm nozzle, 80mm/sec is beyond what a UMO can do for most PLA. You need more like 230C. I know you say the walls are perfect but 10% underextruded walls will typically still look great. The filament is almost surely slipping quite a bit.

Your problem *might* not be undrextrusion but this is the easiest thing to check. Keep your print speeds well below the dark blue line in the graph I linked to above. So for example either reprint but at 240C or slow it down to 40mm/sec.

I believe top infill prints at the same speed as infill. I'm not sure what 130% means as in the recent versions of Cura (last few years) it only allows you to set the speed in mm/sec (advanced tab, speed). There used to be an old print window in Cura where you could set the infill speed % higher. Are you using that? At any rate, keep the infill speed also below the values I mentioned (80mm/sec at 240C or 40mm/sec at 212C).


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By the way it's very common for heavy underextrusion to suddenly stop printing. I don't know why exactly. One theory is that the feeder is grinding/slipping the filament but this isn't always true. Another is some kind of temporary clog but when I start printing again it's always fine. So I'm trying to say all 3 of your symptoms (printing too fast/cold, underextruded infill in the photo - yes that's exactly what it looks like, and suddenly it stops printing) point to the same thing.

I don't truly understand it. Here's a nice photo that shows print speed and underextrusion (severe) and you can see where it also stopped printing near the top of the part (post #2 - purple cube):



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