strange under-extrusion symptom

[bearsfeat 0]

Hi all,

I am getting this strange build quality issue. Take a look at the photos - notice the first 7-9 layers look passable, but then things get bad. This is a UM3 w/ 0.8mm nozzle, PLA - I have played with speed and temp (from default 50mm/s down to 30mm/s - from default 205° up to 235°)  My extruder tension is in the middle ( I could try to increase that...) Any other thoughts?

Thanks

[TestingIsKey 1]

hello bearsfeat!

 

I would like to know your flow rate and layer height. Prints can turn notoriosly bad when using larger nozzles. 

 

 

 

 

[Torgeir 228]

Hi bearsfeat,

 

Well, 0.8mm nozzle default speed is 25mm/s (50mm/s is for 0.4mm nozzle!)

 

So when starting with this nozzle, make a test print take max (10-15) minutes, during this time you can find the proper speed to use with your printer.

 

So; 25mm/s and 205 deg C would be approx default for a 0.8mm nozzle. Should print ok., with this setting.

 

To test, increase speed "a little by little" and monitor temperature, if temperature drop 1 deg C, increase the temperature 2 degrees. Stable, If not, increase speed gradually more, adjust temperature(as above) and so on, do this as long as print looks ok. You will find the sweet spot at some speed and temperature.

 

The main problem here is ozing and blob due to high temperature, so avoid using to high temperature.

 

Tension is only a problem if printer start grinding the filament.

 

Just take care of this issues and I'm sure you would be ok.

 

Good luck

 

Thanks

 

Torgeir

 

 

 

 

 

 

[bearsfeat 0]

Hi folks!  Thanks so much for your input and questions. I will try the suggestions you've given me. I do not remember ever changing the default settings in Cura - So I am surprised that I am printing too fast! Hopefully taht is hte problem

 

BUT...

 

As you can see in the original photos, the first 7-9 layers look really good and this is longer than the "10-15 minutes" for a test print. And this is very repeatable. So, if I ran a test print for 15 minutes using my current settings, I would get good results, but the longer print would end up with issues.

 

My layer height is 0.4mm (sprint) x nozzle 0.8mm x print speed 35mm/s = flow rate 11.2 mm^3/s

This seems high to me... What is recommended for flow rate?

 

Thank you friends!

 

 

 

 

[Torgeir 228]

Hi bearsfeat,

 

I'll think during the first layers there is not much travel and retractions, so it's possible to see some good printing at such steady condition. However, when things change, as deceleration layer change and traveling etc.  When this occurs, -all this hi flow is hard to reduce as the filament parameters is much changed, -as hi temperature reduce the density of the melted filament and this require a number of parameters to be corrected.. Here we will go into the "experimental" mode with our printing and all predictability we want is pretty much reduced.

 

I would think that above 10 mm^3/s is on the high end of the scale, but the limit for UM3 printing your object is something to test for to see.

 

So start with your print, at default speed and temp for 0.8 nozzle. If your object seems to print ok after 5 minute, increase speed until temp drop 1 deg.C then increase temp 2 deg. C. Let it stabilize. If stabilized, increase speed again until drop 1 deg.C. Don't go to fast, make sure that your printer deliver good quality.

 

It is always wise/better to be a notch below max printing speed to make sure that you're working inside the envelop that the printer can deliver good printing.

 

Thanks

 

Torgeir

 

[gr5 2,071]

11m^3/sec should be fine with a 0.8mm nozzle.  I've printed that fast with a .4mm nozzle (barely) and the 0.8 can do (in theory) 4X faster.

 

I'd try lowering the temp a bit.  (190C) I'd look at the layer view carefully to see if the marks are happening at movements.  Exactly at movements.   Larger nozzles are going to leak more.  You can fix this by lower temperatures.

 

Also check your bowden to make sure it doesn't move up or down on either end.

[gr5 2,071]

I took another look at the photos.  Make sure all the printing speeds are the same speed!  There's like 6 printing speeds (leave travel speed fast - 150 to 300mm/sec).

 

Also try cleaning the top 2 inches of the Z screw (where it is used to print these shield holders).  Make sure to get all three grooves as the UM3 and S5 have triple helix.

[bearsfeat 0]

Wow - these are all great tips. I am feeling armed with new tools to solve this - this has been an issue for me for some weeks now. I have many things to do now and I have new hope! Thanks again for your input and suggestions. I do intend to report back with my findings and let the community know how things progressed.