Material Estimation Way Off (Almost 30%???)

[DarthKatana 0]

I just finished a print that had an estimated material usage in Cura (v4.8.0) of 412g but the actual material used is 290g. What would cause this/How do I fix it?

 

I have been 3D printing for a few months now so I'm fairly comfortable with it. My print settings are pretty dialed in and are producing beautiful prints at 0.12mm layer height with PETG. I have also created a custom profile for the Overture PETG that I am using and I feel as though it's spot on. Switching the selected material to the generic PETG increases the estimated material usage to 437g.

 

Custom Material Settings:

Density: 1.30 g/cm3

Diameter 1.75mm

Filament weight 1000g

Filament length: 320m

 

I am using a Ender 3 V2 and the only major upgrade is a dual gear extruder that required me to increase the extruder transmission ratio from 93 to 139.1 (33% increase). Is this the cause? If so, is there any way to reflect this change in Cura? I have been unable to find any such setting, but maybe I'm not looking in the right place.

 

The time estimates are also pretty close as that print was estimated to take 2d5h and actually took about 2d3h so that's not a problem. My biggest issue is I'm printing a large project that takes multiple spools and an accurate estimation prevents wasted filament on the spool.

 

Any help would be greatly appreciated.

Edited March 13, 2021 by DarthKatana

[GregValiant 1,409]

Cura knows the layer height and line width and the total length of extrusions in a model.  The filament diameter allows a calculation of the length of filament used.  From there the density determines the weight.  If the filament diameter or density are inconsistent in "extruder settings" vs "printer settings" or from material to material then I suppose variations could/would occur in the total weight of filament used.  The error you're reporting is huge.  Your Esteps/mm matters to print quality but I don't think Cura cares.  It is noted in the "printer settings".  If that isn't present with the other settings you will need to load the plugin from the marketplace.

[DarthKatana 0]

That confirms my understanding of the calculation. I couldn't find any inconsistencies in the filament diameter or density anywhere. Changing the Esteps/mm had no effect on the calculations. I did another run through the settings and couldn't find anything that would cause it.

 

I'm about to start a 5 day print that's expected to take 868g and I'll see if the error gets worse or stays at 30%.

[DarthKatana 0]

I just remembered that I had a extruder skipping issue during the infill of the print before this one. I thought I had solved it. Could occasional skipping cause that much of a discrepancy though?

[GregValiant 1,409]

If the extruder is skipping then the E number in the Gcode is being met, but filament isn't getting pushed.  The result is under-extrusion.  If the under-extrusion was to fall off to say 50%, then yes, the Cura calculation will appear to be way off, but the reality is that it's the print that is off.

 

Whether it's Cura doing the calculation, or you with your calculator, the amount of filament is pretty easy to figure out.  With Cura, there might be a discrepancy due to certain settings (like Coasting), but it's going to be pretty close and certainly closer than 412 vs 290.

 

I always clean out my hot end before long prints.  It has always been the problem with my Ender and although it's now a Micro-Swiss, I don't trust it to go much beyond 40 hours without a good cleaning and a trim of the bowden tube.  With Silky PLA, that's about 20 hours.  That stuff is just sticky.

[DarthKatana 0]

That makes sense. Funny enough I just switched to a Micro-Swiss hotend yesterday before starting the 5 day print and the original hotend was in...rough shape. It seems there was about of cm of bowden tube stuck at the bottom that must have broken off when I removed the tube for a cold pull.

 

So far the print is going well with no issues so I guess I just need to clean it out more often than I was. I also like the design of the Micro-Swiss hotend much better then the original. I didn't realize that the bowden tube literally went all the way down to the threads on the nozzle until I swapped the hotend; I always thought it stopped at the heat break.

 

Anyway, thank you for your help. I really appreciate it 🙂