Fillament flow not constant

Hey everyone, how are you? So I bought my Prusa i3 in the beginning of the year, and since then had a constant struggle with a lot of things...Most of my problems was sorted out once I figured out the guy who sells it sells cheap chinese knock offs, and I replaced my entire hot end with a top of the range one...but now I have one last issue...

None of my print finish because my flow is not constant at all! Me and my brother (a mechanical engineer) spent the entire weekend trying to find the problem, and we were able to eliminate a few possible issues...

So what we can eliminate as a issue is the following:

- extruder motor slip
- any blockage
- hot end + cooling chamber diameter
- above mentioned is also lubricated properly

Issues we think it may be:

- inconsistant fillament diameter
- Extruder gear slip (specifically the rough part that actually pushes the fillament)
- we even considered that the fillament could have a rapid thermal expansion before it hits the nozzle

So what do you guys think?

Well you want the extruder motor to have enough current to be able to push the filament through but not too much that it grinds the filament if it jams. You want the motor to skip if it jams.

The idler bearing in the extruder needs to be very tight. If you're using a wades extruder tighten it lots. Some people do away with the springs and just use bolts and nyloc nuts.

It's only too tight if the filament gets squashed out of round. Make sure your drive gear hotbed bolt isn't getting clogged which it will do if it's grinding the filament when it jams due to too much motor current. Maybe take your hot end off, and set the current and idler tension without it attached so you can see if the filament is getting squashed and grab the filament to see how much force it takes to skip the motor.

Make sure you have enough heat at the hot end. If it's not hot enough the filament might become very difficult to push through at speed. Try extruding into free air at different speeds for a range of temperatures to get a gauge of how much heat you need. Push it through by hand see how it feels.

What extruder are you using? What filament diameter? 3mm is much harder to push through.

Measure your filament diameter at many points. Check at different angles for oval filament. Make sure when your hot end is assembled that the heatbreak and nozzle mate evenly and are tightened when hot.

Edited 2 time(s). Last edit at 10/03/2016 04:40PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Hey Dj, thanks for the reply!

I think problem may lay with the fillament...I know for a fact that there are no places for the fillament to jam, and I tightend the screws for the extruder very hard.

Im still not sure of the problem

Well changing filament is easy enough.

When I had an i3 with a wades extruder and 3mm filament I was never very convinced of its ability to push filament through with great control, the stiffness of the 3mm filament meant that depending on head position it would struggle to pull it through against the sideways tension the stiffness of the filament generates.

I could mitigate this problem by hanging my filament reel a good 3-4 feet above the printer.

Changing to 1.75mm and there is no such worry, and with e3d titan you almost forget about the extruder - it just works.

Edited 1 time(s). Last edit at 10/04/2016 04:00AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
James@Archi
Hey Dj, thanks for the reply!

I think problem may lay with the fillament...I know for a fact that there are no places for the fillament to jam, and I tightend the screws for the extruder very hard.

Im still not sure of the problem

I would start with the basics and go from motors and step settings, Myself would be to take off the hotend off and using M302 (cold extrusion) and finding out if your steps are correct. I used this as a starting block Triffid Hunter's Calibration Wiki it may give you over extrusion on your result but basically what i do is check when i say to my extruder pass 100mm in 10x10mm jog moves it does that, any differences you can work out what your true steps where your +/- from 100mm.

Once done that I would do 1 layer prints to adjust your idle screws, what I found that when I had issues I would have too much filament getting pushed out, that was due to my idle screw was too tight, but can also stop you from extruding what kind off hotend are you using? is it all metal or has a pfte tube?

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