Determining optimum flow rate for a filament and nozzle

[JohnInOttawa 104]

Good morning!  This might have been covered elsewhere, but my search didn't reveal it, so apologies for any repetition.

 

I've got a range of nozzle sizes with my HardCores as well as a number of non UM materials that don't neatly fit the mold, such as hi temp PLA, etc.

 

I've read at least some of the threads that provide guidance on selecting layer width based on nozzle size, but in most cases there seems to be a bit of a recursive loop as one determines the correct temperature, layer height and print speed to go along with that width.  

 

Some here have already done the homework and identified filament volume for a given nozzle diameter and temperature.  I'd like to understand the process for finding that volume for any filament.  My hope is that having this volume would allow me to dial in the correct combination of line width and layer height for given applications - for example, if I want a strong part with simple geometry in a carbon fibre filled nylon filament, I probably want the widest lines I can manage - so what would be the correct layer height to avoid under or over extrusion?

 

Knowing this would probably have saved me the fun of unclogging my print core after my last Copperfill print.

 

Thank you in advance for your thoughts and forebearance in the case this is a re-hash.

 

John

[yellowshark 153]

Hi John, OK there are a lot of factors involved in your questions and I think it is helpful to split them in two. Generally speaking under extrusion results from a hardware problem. Firstly your filament. If it is wound on the reel really tightly, and being 50%+ through your reel will exacerbate this, then the filament can stick when it is coming off the reel. If the filament is poor quality then its diameter will vary and go beyond specification and stick in the Bowden tube. Good filament is 2.85mm +/- 50 microns. Poor filament can go to 3.0mm and beyond and will stick.

All feed systems have a filament drive wheel which is either at the start of the system and pushes the filament or at the end of the system and pulls the filament, which is how the Ultimaker works I think (?). Allied to the drive wheel is the pressure spring which determines how tightly the teeth on the drive wheel grip the filament. If the spring is too slack then the filament can slip when the drive wheel is trying to move the filament. Conversely if the spring is too tight then pieces of filament can be “eaten” by the wheel and lodge themselves between the teeth; the end result being the toothed wheel that becomes a smooth wheel and again the filament slips. Plus if you have an Ultimaker then the drive wheel is, or was, plastic with a fairly short longevity. My drive wheels are metal and are the same ones that were fitted to the printer when I bought it 5 years ago. The point is you need to keep on top of your drive system.

I have never experienced it but I guess you could have a duff or damaged Bowden tube which would cause the filament to stick.

Finally you have the extruder and nozzle and burnt filament stuck in here will cause under extrusion.

And yes if you print with .300 layers at 100 mm/s with a temp. of 180 and a 1.2 nozzle you will likely under extrude – but you would not do that would you J

 

OK before moving onto over extrusion let us first change your mind-set. In your software settings you do not use layer height to control under/over extrusion. Layer height determines your resolution i.e. the quality of your print. In principal I guess you could use it to control extrusion but then you lose control of quality, bad. You use layer height and print speed to control your quality and time needed to print the model. You use extruder temp. to control the extrusion.

Over extrusion comes from printing too hot and a lot of people print too hot. Just because the specs of a PLA filament say you can print at 220 or 230 that does not mean you should use that temp and yes when I was a beginner I used to use 210/215. These days I use 190 +/- and I cannot remember the last time I went as far as 200. I would advise you to print as cool as possible, for the settings you are using to deliver the quality and time you want.

Looking up a volume table to get the extruder temp – which someone else has produced. Don’t know. Bear in mind that everybody’s printer is different; at any moment in time your drive system could be highly efficient or it may be poor, the same for the guy that produced the table; even different colours of the same manufacturer’s PLA can have  different extrusion characteristics.

I have always followed the discipline that when I try a new filament I test it and find the optimum settings for me.

[JohnInOttawa 104]

Thanks.  I think perhaps you answered a different question (or questions) though.

 

I'll try to think about a better way to ask this question.

John