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I'm printing with opaque grey PETG on glass. The intention is to produce a house number plate, so a shiny, production quality finish on the bottom. For this reason, extruding at 245 °C with a bed at 95 °C, to give a perfect glass finish with no filament lines showing. Smaller test versions have been very promising; this seems to be the maximum temperatures before warping or a severe elephant's foot arises.

However when printing the full-scale version, areas of the first layer of filament seem to go completely "transparent"; there seems to be filament there - you can feel the filament "comb" when you run your finger over it, and it feels a similar thickness to its neighbours.

On the attached photo you might think that those gaps are simply not printed yet, however you can see on the top right corner that it's actually started on the next layer.

print

What could be causing this? Is it a blockage which is interrupting flow, and maybe insufficient filament is being "stretched out"? Or maybe it could be something to do with temperature? Could it be insufficient layer height (I'm using 0.2 mm, but 0.24 mm on first layer, increasing further reveals filament lines, but tested higher and lower on smaller scale with success).

I've tested a range of extrude and temperatures and chosen the temps with the best results; but when I "go large" this always seems to happen. I've also calibrated the bed height using the 3 point adjustment screws on this printer (Qidi X-Plus). (The transparent areas are actually occuring in the center where the smaller test prints where working perfectly, so don't know how it could be to do with this).

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  • $\begingroup$ Welcome to 3dPrinting.SE! I'm wondering if your extruder head is too close to the bed on the initial layer? If it's too close, you could be getting too much squish, causing it to be thinner than you'd expect. Just a thought. $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Feb 6 at 20:09
  • $\begingroup$ Thanks @Paulster2. I did think this myself; which is why I raised the initial size to 0.24 from 0.2. I have to point out that all of the rest of the print (at this point) is the same level, and printed perfectly, so maybe it caused a brief blockage I don't know...? Anyway I'll give some higher initial heights a try and see what happensm ta! $\endgroup$ – Rab Feb 6 at 20:12
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    $\begingroup$ I'm not positive, but I thought layer height has to do with thickness, not with how far your extruder is off the bed? I'm talking about when you level your bed, if your head is too close to the bed, it might cause the issue you describe. $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Feb 6 at 20:14
  • $\begingroup$ @Pᴀᴜʟsᴛᴇʀ2 Maybe all of your upvotes for the comment suggest people know differently, but as far as I was aware layer height is synonymous with thickness - it raises the extruder from the bed. Of course the levelling calibration also affects the extruder's distance from the bed. The bed is levelled - But I think you're on the money more generally that it is down to the extruder's height from the bed, it's just stems from the initial layer thickness specified in the splicer; it's causing squishing as you point out. I'm testing different settings now. $\endgroup$ – Rab Feb 7 at 1:27
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    $\begingroup$ Are you using Z-hop? Is there any play in the Z-axis direction? It appears that parts of the first layer are printed much thinner than other parts, can you confirm this in your question? $\endgroup$ – 0scar Feb 7 at 7:28
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PETG becomes transparent when the layers completely fuse. Translucency is from incomplete adhesion or voids left. Try small increases to flow or print width to get slightly better fill - or slow the speed (but speed might not affect how much material is output).

Also, I see the top surface has a pattern on it. My FDM printer always does a similar thing and it will take tuning to get it smooth. If you see the pattern repeating consistently, it is possible the extruder stepper (or its driver) is starting to fail. I've had that too.

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Are you using Z-hop? Is there any play in the Z-axis direction? It appears that parts of the first layer are printed much thinner than other parts.

What can happen if there is a little play in the Z-axis direction that the nozzle doesn't return to the same level after a Z-hop movement (e.g. backlash in the leadscrew nuts).

The "transparent" printed part appears thinner, this must indicate that the Z positioning is not up to par.

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