Warning: Don’t try this at a stock TAZ, or at least at your own risk! The IGUS bushings may start to “smoke” at the speeds mentioned below!
I was thinking about harmonic vibrations (visible on external perimeters) today and it would be nice to hear your opinion on that.
Have a look at my post with picture from the Openbuilds X axis mod: https://forum.lulzbot.com/viewtopic.php?f=16&t=2252&start=280#p23904
I got straight walls, but at some speed there is a ripple in it which comes from harmonic vibrations. I have such ripple in nearly all of my prints when the perimeter speed is not <40mm/s. But on the other hand, there are piercets high speed trials at 400mm/s and his cube is perfectly straight. So I did some tests today to see where the vibration is coming from and how it is related to movement speed.
There is the very useful (but badly documentated) DryRun feature of Marlin which can be used to “print nothing” at different speeds sending “M111 S8” to the printer. So I sliced a test cube (100x100x20) with a single perimeter at 100mm/s. This way I was able to set the real print speed by the speed % on the TAZ display, 60% means 60mm/s for example.
I let it run, with a finger on the extruder body to feel whats going on (same is also true for the Y axis by the way):
.) Starting from low speeds (20mm/s), the extruder body is vibrating a lot and it gets worse as the speed is increased until 80mm/s. The Openbuild Rail and the stepper motor mount are not vibrating, but you can feel the same amound of vibration also on the stepper itself. So source = stepper, transmitted by the belt.
.) Going from 80mm/s to 100mm/s, the vibration on the extruder body gets lower rapidly. The stepper is still vibrating, but the X axis “sledge” seems to dampen this higher frequencies.
.) At about 100-120mm/s, there is no feelable vibration left on the extruder.
With this results, I did my first real high speed run, a test cube with 40x40mm at 150mm/s. To keep the extrusion rate in an acceptable limit, the layer height was set to 0.1mm (=7.2mm³/s). Tada, one of my nicest prints ever! Zero ripple on the walls, only my stock Y axis had a little bit of trouble while accelerating to 150mm/s which results in a short but heavy corner ringing on the Y side
Somebody here who had a simmilar observation? It would be intresting to know how the aluminum backplate for the Openbuilds Mod compares to my printed one regarding to this vibration dampening.