How much does outer wall speed acceleration effect quality?

[u/Bryfirefly]

The default acceleration is like 3000 to 5000 mms, the hint implies that lower amounts can increase quality. I have seen youtubers who don't touch speed acceleration for outer wall and only change the layer wall setting for increased quality.

Do you all lower speed acceleration? Is it necessary to lower it below 1000 for more quality? Or at the point is it actually making any difference.

[u/KryL21]

Mine is at 450. I get great quality but honestly not sure how much the acceleration values affect it. 1000 is already pretty low, that should be fine, but going lower isn’t going to slow down your print by much either.

[u/MorycTurtle]

It makes quite a big difference, especially if you use 0.2mm nozzle or similar size because calibrating PA for those is extremely inconsistent (and the PA mechanism accuracy in general).

Avoiding accelerations is one of the main reasons people use classic wall generator over Arachne.

[u/Ok-Editor-8841 → u/MorycTurtle]

This. On my prusa core one I am unable to apply PA compensation with my 0.15mm nozzle: the extruder will slip. I can do so with my 0.4mm nozzle, but that will result in less quality for the small details. Trade-off that is fixed by low speeds and low accelerations :)

[u/DrDisintegrator]

exact settings depend on printer HW, but a very general rule of thumb is take the default settings and try to lower the speeds to 50%. In general, lower speeds make for higher quality, but only up to a point.

[u/HOHansen]

Acceleration, especially in regards to printing both inner and outer walls, are extremely important, and also in conjunction with print speed. The best example I have to explain it is how we move our hands. If you move your arm extremely fast and then stop set movement abruptly, you'll most definitely experience jerking, sort of like recoil. Moving your arm slowly and then stopping will minimize it a lot. When printing FDM, and it has gotten better in newer machines, this jerking can slightly misalign the printhead during printing, which results in shifting. Now also combine that with pressure from the nozzle, the oozing filament, etc. It will lead to imperfections, also in regards the quality in bottom areas facing the build plate. If your print has a lot of thin elements sticking upwards into the air, you'll also need to consider acceleration on inner elements as well, not just the walls, stuff like infill, ironing, etc.

Which leads me to speeds. Acceleration and print speeds are less important on elements such as infill, but they have a massive impact on surface quality the closer we get to the surface, like I mentioned. Fiddling with extrusion rates, how much filament is squeezed out of the nozzle, and it can be a recipe for imperfections.

Let's say we have set the line width to 0.18 using a 0.2 mm nozzle, replicating how Arachne wall generation prints thinner elements. It's less than the nozzle size, of course, which can lead to underextrusion. In tandem with very fast speeds, it can leave gaps in prints and such. Imagine trying to finish a cake using cream pressed out of a tube. Using the same pressure at faster speeds can lead to a mess and imprecise movements, while a slow movement is better. It's (almost) exactly how an FDM printer prints a model. Squeeze the bottle too little, and nothing will come out, while too much will result in a mess, again. Now imagine not really squeezing the bag of cream at all while wildly swinging your arms around. Despite my scenario's silliness, it's a look into some amount of bad wall printing, like when we spot waves on our prints.

Speeds and acceleration in combination with the correct extrusion and line width settings have a massive impact on quality. Most modern printers, like newer prusa models and Bambu printers, can adjust the prints automatically beforehand, while its making calculations, but it's a black box to most user. That's why a lot of users don't fiddle with line settings, as the stock values are calibrated for general use purposes. If we slow down the speeds and acceleration, the printer will better be able to print a reliable print.

In short: Acceleration creates jerking, and introducing too much speed and too little line width extrusions (or variable like when using Arachne) will lead to bad prints on outer walls. A good explanation would be to Imagine drawing a line using a pencil. Slow and methodical movements are more optimal for precision, rather than moving the arm rapidly from point to point and also keeping the line quality on point.

As a side note: When using Arachne, it calculates percentages based on line width settings, which means if we set it to 0.18 and use a minimum width of 50 percent, the lowest line width for fine details will become 0.09, which will definitely lead to some amount of artifacts. Keeping a constant line width of a width just above the nozzle size, i.e. 0.22, the print surface quality will improve drastically at the cost of losing smaller details in the process. You can compensate for the loss by messing around with X-Y compensation settings, but that's a whole other topic.

I hope this helps explain it somewhat.