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Question Cylindrical parts not quite "round"

billgeek

Member
I'm not certain if this is hardware, firmware or slicer related, but I've been running my Trident for about six months now. I thought the print quality is pretty decent, but I've since purchased a Bambu Lab P1S and this made me realize what "round" actually means.
Circular objects on the Trident tend to come out as "segmented" lines.

I followed and dialed in my printer using the excellent guide by Ellis for tuning the machine and am using BambuStudio to slice my model.
I've tried this with "Arc fitting" enabled or disabled on the Trident, but the result remains the same. (I needed to add "gcode_arcs" to the config file on my Trident and set the resolution to 0.25mm - any lower and I get "timing" issues)

This first picture is from the Trident. Notice the "wobble" on the lower half below the knurled grip. I took this picture in the worst possible light to exaggerate the issue:

PXL_20240130_183315893.jpg

This next picture is from the P1S. Aside from a few lines appearing slightly darker, the walls on the lower half are perfectly circular. (This picture was also taken in the worst possible lighting conditions)

PXL_20240130_183330582.jpg

I also own the Creality K1 and it looks the absolute worst, with the lines creating a texture on the cylinder:

PXL_20240113_134247218.jpg


So I guess the question is: What could be the cause of this, and how can I go about addressing the issue? I fully realize that the Bambu is a proprietary machine and all that, but at the end of the day it's "just another" CoreXY machine.
 
Doesn't this essentially come down to the steppers?
Steppers have a finite resolution, round can not really be round, ever.

Now i am really curious how the Bambu gets this roundness.
 
This is VFA and comes down to tuning. Being Machine or slicer.
The K1 picture looks like to much belt tension to me. Each like looks like it can match the belt teeth.

As far as your Trident goes, you can try slowing down a little in speed and accel. Or try tuning the motors and steppers more.
 
The Trident print looks more glossy, as if it was printed at a higher temp? Printing at lower temperatures will make the filament more viscous - which provides a natural "smoothing" to the extrusion flow.

Also, check your model to see how the facets look. It's a bit counterintuitive, but the better a printer is tuned, the more accurately it can reproduce the original model - INCLUDING its faults.
 
Doesn't this essentially come down to the steppers?
Steppers have a finite resolution, round can not really be round, ever.


Actually stepper don't have a finite resolution. They can be driven in a continuously, smooth, non-stepped mode. After all, a stepper is nothing more then a two-phase BLDC motor with many pole pairs. That said, you =are not going to be able to drive them in a stepless mode with the electronics and softwarte typicaly found inside a Voron printer.

The other thing I'd look into is the idlers. Are you running the toothed side of the belt against a flat pulley? This is a design error and should be fixed. I'd bet you Bamboo printer does not have the same error. Gates makes toothed idler pulleys and also smooth pulleys that have a better profile than stacked flanged bearings.

Bamboo has raised the bar simply by doing everything right and by not limiting itself to commodity and plastic parts.

Running a stepper in contiinous mode requires quite a lot of hardware. Each motor needs a good rotray encoders and a typical MCU can drive only one motor befor it runs out os "compute power". Youcan Google "FOC" otr "Field Oriented COntrol" for details. I've got a demo running on my desk. An RP2040 does fine, an ESP32 does better. A mid range STM32 would work too. Then you need a $15 sensor attached to the motor shaft. Ho, and you need to measure current in both phases.

The other op=tion for continously motion is industrial servo motrs as found on higher-end machine tools. But these are $200 motors, even in the tiny sizes we needs and the controllers are $100+ per motor.

The next thing we need to do is get away from STL files and use CAD files like STEP. These file contain the perfect precision mathmatical models of the shape, not a bunch of straight-line triangles.

And while on the subject, we need to print with the Z-motors running and not just on slice planes. Look at how 3 and 6 axis CNC machines work.

The future is exciting. There is so much more to be done. Today in 2024, the low-hanging fruit is mostly gone, getting much better will take a LOT more work and cost.

But for now? Try setting the number of microsteps as high as you can and print slower. And do NOT accept a 0.25 mm error. That will put flat sides on your round parts. If the computer can't keep up, go slower.
 
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Also, check your model to see how the facets look. It's a bit counterintuitive, but the better a printer is tuned, the more accurately it can reproduce the original model - INCLUDING its faults.
I think the Bambo was printing the exact same STL file as the Trident. The Bamboo printer is doing a better job of it. The question is "Why?" what is it doing that the Voron printers are not doing. It might be informative to look at the g-code.
 
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