Periodic setting based under-extrusion

[Alexandergubski 0]

I see major under extrusion problems that seem to be random from job to job. I use Wanhao Duplicator 6 that is very well tuned and I get perfect models when there are no g-code glitches. Brim seems to be printed normally and rest of the model looks like was sliced using 3mm filament even though everywhere in settings it is 1.75mm. Increasing flow to 250% helps but it would be good to get to the bottom of it. See attached image as an illustration.

[gr5 2,172]

I find that increasing flow over 110% is a losing situation but if 250% truly helps a lot then you are probably right - it is slicing for the wrong filament diameter.  The actual ratio is 265% (1.75 versus 2.85 filament) so try that.

 

I would look at a line segment in the gcode and multiply it out and see if the gcode is wrong.

 

Anyway if you want to set to 1.75 filament you have to configure BOTH the printer and the filament.  Cura has lots of 2.85mm (or 3mm) filament in it's database so you have to be careful to use 1.75mm filament profiles in cura.

 

[Alexandergubski 0]

Thanks! Could you pls expand on "I would look at a line segment in the gcode and multiply it out and see if the gcode is wrong."?

 

I didn't know that you could add multiplier to affect feed rate...

 

 

[gr5 2,172]

I would test the gcode to be sure - absolutely sure if it's assuming 3mm versus 1.75mm.

 

So for example you can look at these 2 gcodes:

 

G1 X123.7 Y100.0 E5.000

G1 X133.7 y103.0 E5.010

 

Now you can find the diff in X (10mm exactly) and the diff in y (3mm) and find the hypoteneuse (square root of the sum of the squares) and determine the length.  The height is your layer height, the width is "line width" you specified in cura.  Multiply those 3 values to get the volume of plastic needed for that.

 

Now take the difference in E values (here it's 0.01mm).  Now figure out the volume that .01mm of linear filament creates for 2.85 versus 1.75 filament and see which of those matches the expected volume.  (volume of cylinder is area of cross section times length.  Area of cross section is 2 pi r squared)

 

That's what I meant by "do the math".

 

[Alexandergubski 0]

Now I get it. Thanks a lot for explanation

[gr5 2,172]

Wait - so one job prints fine and the next not so well with no changes to profile or settings or filament?

 

If that's true then you need to talk to wanhao experts but I can think of one explanation that would affect all bowden printers and that is excess retractions.  What is your retraction distance?  I've seen prints where there were over a kilometer of retractions in a single print (yes, truly).

 

Even a small print can fail if you have more than about 10 or 20 retractions on the same spot of filament.  You can reduce retractions if you play with cura settings.

 

This is one of about 20 possibilities on a Ultimaker printer.  I don't know anything about wanhao printers.