First Layer height behaviour in PrusaSlicer
 
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Minos
(@minos)
Active Member
First Layer height behaviour in PrusaSlicer

Hi,

I have been trying to create a PrusaSlicer profile for a custom marlin based 3d printer, and I have come across this setting. Most slicers have a "First Layer height" setting but the implementation varies widely.

For example in Simplify3D < v4.1 it needs to be set to 90% the models layer heigh, at which it will be keep the extrusion flow constant, but will get the nozzle closer to the bed aiming at squeezing filament for increased adhesion.

Slic3r and Cura tend to adjust the flow rate accordingly, so the recommendation is to increase the value up to 35mm for a 40mm standard nozzle. If you need to achieve the same effect as S3d you need to adjust the z offset.

To make things even more fun, many  printers, will override the setting set by the slicer if it appears to be unreasonable ( i.e a prusa with auto-levelling, if the slicer setting is too low that may damage the bed )

My question ii what is prusaslicer's intended behaviour. I could not  find any formal documentation to describe if it adopted the pre-fork slic3r one.

  1. Is the current tooltip up to date with the code?
  2. Does the setting affect flow rate?
  3. Should we be using the default setting? And if so what is the default? Is it calculated as a function of nozzle size?
  4. Is it more a setting aimed at dealing with wrapped beds, while "first layer width" is aimed at increasing overall adhesion?

Thanks

 

Posted : 12/11/2019 3:25 pm
bobstro
(@bobstro)
Illustrious Member
RE: First Layer height behaviour in PrusaSlicer
Posted by: @minos197

[...] My question ii what is prusaslicer's intended behaviour. I could not  find any formal documentation to describe if it adopted the pre-fork slic3r one.

I haven't gone through the code, but in general, PrusaSlicer (PS) will try to do what you tell it. If you specify a 0.20mm 1st layer height, it will calculate the appropriate flow and movement at 0.20mm. Unlike Simplify 3D, it doesn't "help" by tweaking flows behind the scenes. The only catch is that there is a minimum 1st layer height limitation of 0.15mm due to the software endstops used on the Mk3. Not sure what the effect will be on a non-Prusa printer.

  1. Is the current tooltip up to date with the code?

Again, have not vetted the code, but the current tooltip matches how the sliced part prints. A 1st layer height of 0.20mm or greater is recommended for good adhesion, but not mandatory. 

  1. Does the setting affect flow rate?

Only in that it calculates flow for the height you've selected. PS does not add a bit of over-extrusion on the 1st layer.

  1. Should we be using the default setting? And if so what is the default? Is it calculated as a function of nozzle size?

0.20mm is a good default for a Prusa printer. For other printers, it will depend on how level your bed is. A thicker 1st layer may help make up for an uneven surface. I've used 0.20mm for everything with nozzles from 0.25mm to 1.5mm and it provides a solid foundation for the rest of the print. The only caveat is that smaller (0.15, 0.20mm) nozzles may not work well with that layer height. Staying within 80% of the nozzle size for layer heights is recommended for best adhesion, especially on the critical 1st layer.

  1. Is it more a setting aimed at dealing with wrapped beds, while "first layer width" is aimed at increasing overall adhesion?

That's what I've understood after working with PS for a while, yes. I just finished some large parts printed with a 1.0mm nozzle using PETG and built it all on a 0.20mm 1st layer. Those settings have been very reliable for me. I have read of thicker 1st layer heights suffering from uneven cooling. Too thin and the uniformity of the bed comes into play. 0.20mm is thick enough for good flow, but not so thick as to introduce cooling issues.

 

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and miscellaneous other tech projects
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Posted : 12/11/2019 4:04 pm
Sembazuru
(@sembazuru)
Prominent Member
RE: First Layer height behaviour in PrusaSlicer

I haven't experimented, but my thought experiments seem to indicate that in PrusaSlicer a wider first layer should give more squish against the bed. My thinking is when the melted plastic is squishing sideways to achieve the layer width, there is also a certain amount of downwards force as long as the molten plastic is still under the flat of the nozzle tip. On the first layer this downwards force would (should?) squish the plastic into the bed more.

This usable width for downwards squish is, of course, up to the physical width of the flat on the nozzle tip.

This post was modified 3 years ago by Sembazuru

See my (limited) designs on:
PrusaPrinters - https://www.prusaprinters.org/social/1448-sembazuru/prints
Thingiverse - https://www.thingiverse.com/Sembazuru/designs

Posted : 12/11/2019 7:02 pm
martin.b23
(@martin-b23)
Active Member
RE: First Layer height behaviour in PrusaSlicer
Posted by: @bobstro
Posted by: @minos197

[...] My question ii what is prusaslicer's intended behaviour. I could not  find any formal documentation to describe if it adopted the pre-fork slic3r one.

  1. Does the setting affect flow rate?

Only in that it calculates flow for the height you've selected. PS does not add a bit of over-extrusion on the 1st layer.

I used a 0.6-nozzle recently and got very weird first layer when using other height than 0.2mm. I aimed for 0.35mm for all layers but the first looked absolutely awful.

My guess was that the flow was hardcoded for 0.2mm because when using this everything looked fine.

I recently rebuilt the printer to a mk2.5s so it's back on 0.4mm nozzle and all software is latest and greatest for the moment but it would be very appreciated if someone using bigger nozzles could test a first layer at 0.35mm or more and tell me how it looks.

I tried to write this text outside the quote but failed miserably so the post probabvly looks strange.

Sorry for that.

Posted : 24/01/2020 11:08 am
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