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[Klipper] How can I read the layer height from a gcode file and pass it on as a variable? (lemmy.world)
submitted 3 months ago by papalonian@lemmy.world to c/3dprinting@lemmy.world
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Hi all, got a bit of a technical problem I'm trying to solve and I've got very little programming experience.

Basically, I'm trying to create a folder with a bunch of filament profile cfg files, with things like retraction distance, temperature, flow rate etc preloaded into them. That way, I can slice a model for a 0.6mm nozzle, send it to Klipper, and run it with any filament I want without having to re-slice, just change which cfg file is loaded.

This is going pretty well and I've figured out how to get most of what I want into the cfg. However, I want to limit my print speed by my maximum volumetric flow rate, a variable that Klipper does not support (and Kevin has more or less denied requests to have it added). To solve this issue, I want to limit the max speed instead, using a formula like this:

print speed = (max vol. flow) / (nozzle width) / (layer height)

(max vol. flow) and (nozzle width) would be defined manually by me for each profile. The only issue is (layer height), which of course can change from print to print. I know that my slicer puts the layer height and total number of layers in the header of the gcode, I also understand that that's where Klipper gets this info from and how it displays those numbers once you've selected a file. What I'm having trouble figuring out is how I can send that number into the above formula; I found this which seems to be almost what I need, but I can't figure out how to use the "print_stats object" in my cfg.

A potential workaround is to find my maximum layer height for each nozzle/filament combo and set the max speed assuming that later height, but if I'm printing something at say half my maximum layer height that's going to severely unnecessarily reduce my print speed.

Any advice?

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[-] algorithmae@lemmy.sdf.org 3 points 3 months ago

The Z value for G01 would be your layer height

[-] papalonian@lemmy.world 2 points 3 months ago

I'm not trying to find what my layer height is so that I personally know it, I'm trying to get the gcode to pass that information directly into a variable so I can use it in an equation

[-] reffu42@kbin.run 2 points 3 months ago

Not sure what slicer you use, but in prusa slicer you could just set the variable in the machine startup code with the layer_height placeholder (or you could modify the start_print macro to pass it in). theoretically, you could also set it in the layer_change gcode in your slicer to account for variable layer height as well

[-] papalonian@lemmy.world 3 points 3 months ago

I've managed to get Cura to display the layer height in the startup code, what I can't do is get Klipper to do anything with that value.

If I try to create a variable and define it's value as {layer_height}, Cura doesn't pass the variable's value, instead it just defines the new variable's value as "layer_height"

[-] anguo@lemmy.ca 2 points 3 months ago

Could you set the speed in the slicer instead of Klipper?

[-] papalonian@lemmy.world 1 points 3 months ago

I could, but the entire purpose of what I'm doing is to avoid having any material-specific settings set in the slicer, so that re-slicing between filaments isn't necessary.

I actually got this working last night, I had to learn a lot about how variables work but it works like a charm:

  1. Slicer names a variable for layer height in the start gcode of every print

  2. cfg file for each filament contains a max volumetric flow for that filament/nozzle

  3. a macro takes these values and the layer height and finds a max speed for the given parameters

  4. a second macro assigns this value to the "speed factor" percentage

  5. print speed in slicer is set to 100mm/s, travel speed is set to 9999mm/s; say the equation limits my speed to 55mm/s, it sets speed factor to 55%, now moves with extrusion will be 55mm/s (travel will be 5500mm/s but limited to 500mm/s by printer's max speed)

All other filament/nozzle settings were really easy to bake into the cfg file, there's just no official Klipper support for a max volumetric flow so I had to jank this system together.

[-] anguo@lemmy.ca 1 points 3 months ago

Glad to hear you got it working!

[-] ExcessShiv@lemmy.dbzer0.com 1 points 3 months ago* (last edited 3 months ago)

Do you often need to print the same file in significantly different materials with the exact same settings in support, infill type/percentage, wall thickness, rafts etc.? If I want to print something in e.g. PLA and ASA, I need fairly different slicer settings that would require re-slicing anyway.

[-] papalonian@lemmy.world 1 points 3 months ago

The only thing you mentioned that I would ever need to change between materials is supports, and I very rarely need to print anything with supports. Theoretically it makes sense to reslice for walls and infill so you can make thinner/ lighter models if the material is stronger, but I'd prefer the ease of switching to a perfectly dialed in profile over the occasional savings in material.

The only thing that really needs anything special from the slicer in my experience is PETG with it's funky bridging, everything else can be ignored if you have your material settings perfect. I'm getting much better quality prints with these quick profile swaps than I was quickly re-slicing things with mostly-good settings.

[-] ExcessShiv@lemmy.dbzer0.com 1 points 3 months ago

Fair enough, I've found that properly tuned material settings work best for my setup WRTG consistent quality.

[-] papalonian@lemmy.world 1 points 3 months ago

Yup exactly, I was being lazy previously and if the settings (ie retraction, flow, pressure advance etc) were "close enough" I wouldn't bother re-slicing, would just reprint and accept the good-enough quality. Now, no need to re-slice, and I get the spot-on material settings I've calibrated

[-] fhein@lemmy.world 1 points 3 months ago

The only issue is (layer height), which of course can change from print to print.

Technically not the only issue 😀 it can also change from layer to layer.

Maybe calculate it from the length of filament being pushed out / the length of the movement * filament cross section? I'm on my phone so I can't check right now but that info should be possible to extract from the gcode iirc

[-] papalonian@lemmy.world 1 points 3 months ago

Technically not the only issue 😀 it can also change from layer to layer.

I realized a little bit into finding a solution that this would be a limitation. I'm using Cura which AFAIK doesn't support traditional "variable layer height" like prusaslicer. It does however allow for different layer height for infill; if I ever decide to do that, I can just adjust the infill print speed accordingly.

I actually got this working btw, I had to learn a bit about how variables work in Python/gcode but it's working like I charm! I find my max volumetric flow, set it in the material cfg, and it just runs prints right below my max extrusion rate. Everything has come off the printer looking perfect in between filament types, no re-slicing required!

this post was submitted on 04 Aug 2024
17 points (94.7% liked)

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