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So, I'm pretty new to 3D Printing, and to quote Spock from Wrath of Khan I would say "He is intelligent, but not experienced". Now everything I have been reading about Z-offset seems to talk about a 0.2 mm gap and using a piece of paper.

Wishing to be accurate, I have tried to use my 0.2 mm feeler gauges and this is too high.

However, the thickness of paper depends on the GSM (grams per square metre). A Google search tells me that the average thickness of paper is ~0.1 mm but how can we be accurate with this variation.

I tried using a 0.1 mm feeler gauge and even this seemed too high. Is this because of the lack of give in the metal? Anyway, I have now settled for a Lotto slip (UK Lottery) which has a thickness of 0.1 mm and seems to allow me to set a good offset.

However, I would welcome someone who can explain the science behind this.

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They are all generic guidelines. Don't count on them too much.

Rather, get an approximate Z-offset value, then print a solid 30x30x5 mm cube.

If, starting from the third-fourth layer, you see some over-extrusion, you need to adjust the extrusion multiplier or the E steps calibration and reprint.

Once the solid cube looks good starting from the third-fourth layer up, then you can tune the Z offset by printing a cube which is only 0.2 mm high (or 0.25 mm, or whatever your first layer height is).

If you see over-extrusion, the Z offset is too big. If you see visible gaps between extrusion lines, the Z offset is too small.

If unsure, better get some small remaining gaps rather than overextrusion and excess material.

The idea is that extrusion issues in the first layer can be caused either by the offset or by the multiplier, so you must adjust the multiplier first by looking at the print after about 1 mm height (the first layer issues tend to disappear after some layers). Once you know the extrusion is right, set properly the first layer.

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  • $\begingroup$ That's really useful advice. I'm trying to configure Marlin from scratch and there is definitely head scratching going on. $\endgroup$ – Davies-Barnard Feb 4 at 17:17
  • $\begingroup$ @Davies-Barnard and don't forget that the offset needs to be checked periodically, since the nozzle wears out not by widening itself (usually), but rather by getting shorter, so the Z offset increases $\endgroup$ – FarO Feb 4 at 18:37
  • $\begingroup$ Personally I use Klipper, so that everything is done via config file without any flashing, but then a Raspberry Pi is needed, so people may not like the idea. $\endgroup$ – FarO Feb 4 at 18:38
  • $\begingroup$ ...then, after swapping filaments, you will notice that you have to re-calibrate the rate flow, because the other one is softer and teeth bites it deeper. For the Z, remember to calibrate it with bed already heated (I use piece of glass over printboard, this setup bends a bit, I played a lot with springs and wote "front" with marker on glass to remember how to put it after washing). Change is inevitable. $\endgroup$ – octopus8 Feb 5 at 2:40
  • $\begingroup$ @octopus8 the offset is independent of bed temperature. It is the probing which has to be done when warm $\endgroup$ – FarO Feb 5 at 10:28

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