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UM3 Feeder limitations on print resolution

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Posted · UM3 Feeder limitations on print resolution

Does anyone have any experience regarding the minimum resolution I can print with? Any help or ideas shared are highly appreciated 🙂

 

According to the UM3 manual, the layer resolution is:

Quote

 

0.25 mm nozzle: 150 – 60 Mikron

0.40 mm nozzle: 200 – 20 Mikron

0.80 mm nozzle: 600 – 20 Mikron

 

 

Thus, I expected the minimum printing resolution to be x: 0.25mm; y: 0.25mm; z: 0.06mm However I'm not getting good results for my fine structures.

 

I then had a look at the Ultimaker 3 feeder:

  • Moons 17HD6482_01N stepper motor (200 steps/round)
    • powering a 11-tooth gear
  • Transmission to a 36-tooth gear
    • powering 10mm diameter feeder wheel

These characteristics lead to a minimum filament feed lenght of: 1/200*11/36*10mm*3.1416 = 0.048mm / step

For the 2.85mm diameter filament, I thus assume a minimum extrusion volume of 0.048mm*(2.85mm/2)^2*3.1416 = 0.306mm³ per feeder step.

For a line printed with the 250 Mikron nozzle and 60 Mikron layer height I get a single line minimun printing lenght of 0.306/0.250mm/0.06mm = 20.4mm per feeder step

This value seems quite high I think. Am I really limited to print such long lines when it comes to a small printing layer hight? Is there maybe an errror in my calculations and assumptions?

 

Does anyone have any experience what happens when the amount of required material for a structure is below the minimun volume to be extruded by one feeder step? (e.g. printing a single line, 5mm long, 60 Mikrons layer height, 0.25mm nozzle)

I have the impression that in this case, the feeder stays still and the print core moves along the printing path, but doesn't extrude/print significant amount of matrial. However, I couldn't confirm my suspicion so far. Probalby I need to check my printed structures under a better microscope to measure width and hight of my line/layer.

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Posted · UM3 Feeder limitations on print resolution

0.048 mm/step is what you came up with.  Usually this is shown the other way around:

20 steps/mm

However the actual value on the UM3 I think is 369 steps/mm (according to some json file in the firmware I just checked).  UM2 is 282 steps/mm and I think the UM2+ and the UM3 are similar and have more steps than the UM2.

 

The difference from what you came up with (20) and 369 is about 18X.  I think it's because there are 16 microsteps per step so the actual value is probably 369/16 or 23 whole-steps/mm which comes out to 0.071mm/step.  Your math seems pretty good but the effective diameter of the feeder sleeve is probably closer to 8.7mm which makes your formula work out.

 

Anyway, 16 microsteps is about right - that's the same value used for X,Y and E for UMO,UM2,UM2+ and the Z drive for some of those is 16 microsteps and for some it's 8 microsteps.

 

Anyway what's a microstep?  Well you can look it up in wikipedia servo articles.  Basically there are 2 sine waves sent to the stepper and you can change the phase slowly and get as many substeps as you want but the chips that Ultimaker uses in the UM3 I think only go to 16 microsteps.

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Posted · UM3 Feeder limitations on print resolution

Please note that you can also get 0.15mm and even 0.1mm cores for the UM3 at my store (yes, I'm biased) or at 3dsolex.com.

 

Printing at 0.25 and smaller nozzles requires lots of experimentation to get the settings right.  I've printed some amazingly small stuff with 0.15mm nozzles.  One problem is cooling - I had to print many objects so that each object had time to cool while printing the next object over.

 

I think these were 0.1mm layer and certainly 0.15mm nozzle.

 

a.png

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Posted · UM3 Feeder limitations on print resolution
22 hours ago, gr5 said:

However the actual value on the UM3 I think is 369 steps/mm (according to some json file in the firmware I just checked). 

 

 Your math seems pretty good but the effective diameter of the feeder sleeve is probably closer to 8.7mm which makes your formula work out.

 

Anyway, 16 microsteps is about right - that's the same value used for X,Y and E for UMO,UM2,UM2+ and the Z drive for some of those is 16 microsteps and for some it's 8 microsteps.

That's good to know, thanks for your help! Both the microsteps and s slightly smaller feeder sleeve diameter make sense. As the feeder sleeve has some sort of bumps on its surface (probably to increase grip) I might have measured the outer diameter (including the bumps) rather than the actual diameter of the feeder sleeve.

 

With 369 steps/mm, the 250 Mikron nozzle and a layer height of 60 Microns I would get a single line minimun printing lenght of ((2.85mm/2)^2*3.1416) * (1mm/369steps) / 0.250mm / 0.06mm = 1.15 mm per step

That seems a lot more realisitc than the 20mm I calculated in the first place and might fit the detailness of your model prints. I was hoping to create even smaller structures, but probably that's how it is 🤔 I will print some more test lines...

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Posted · UM3 Feeder limitations on print resolution

Well you could convert to 1.75mm filament.  In your specific case - if you are printing a lot of 0.25mm parts - I think it's worth doing.  3dsolex sells a conversion core.  It's a bit tricky since you have to change the bowden but really - after you've done it a few times you can swap cores in just 3 minutes.

 

3dsolex also has a 0.15mm nozzle and 0.1mm nozzle for that conversion core.  I sell this stuff too.

 

The existing UM3 feeder works fine for 1.75mm filament.

 

Assuming 1.15mm per step calculation is correct (it sounds right) then with 1.75mm filament you will get 1.15*(1.75^2)/(2.85^2) or 0.43mm per step at 0.06 height (again - I prefer 0.1mm layer height - I'm not sure why I need higher resolution in the Z than I'm getting in X and Y.  But maybe if I tried it I would have my answer 🙂

 

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Posted · UM3 Feeder limitations on print resolution

Doesn’t retraction also play into this? If you print a shorter line than one step’s worth of feed, it will retract at the end of the feature.

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