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Extrusion flow

Posted by DRepBRo 
Extrusion flow
March 09, 2013 05:57AM
Hi, I have my RepRepPro Mendel for a week now, trying to get good quality prints, (very) slowly improving (still a long way to go). On some issues, plastic flow in particular, I find I could use some help, it will be greatly appreciated.

  1. I can't get a consistent flow. After starting a thread, for the first 30mm of extrusion (roughly) flow seems ok (I get good solid walls here) - but for the next 30mm or so there is almost nothing (or much less) coming out. Most noticeable on perimeters, where I get thinner / weaker / messy / saggy walls - it happens consistently in same spots. Also noticeable on infill where I get (much) thinner or missing patches. I made sure my hot-end is clean, sliding the filament down the tube goes without impediment, extruding hot plastic by hand works nicely. I tried high and low (and none) retractions, lowered the feed-rate, fiddled with Oozebane, Dwindle, higher / lower temperatures, tightened the hobbed gear, etc - I must have missed the right settings. Any advice please ?
  2. I observe the infill pattern, high solidity - the filament should be put with constant distance between adjacent lines. My infill lines come in noticeable batches - a pack of denser (closer together) lines (for a good 2mm in the X direction), then some wider apart (1mm or so in the X direction) - so I get a pattern: dense, loose, dense, loose, ... My thinking: maybe some impediments on the X axis prevents the X motor to maintain constant speed. I will check that, but some advice would be great.

Edited 2 time(s). Last edit at 03/09/2013 06:00AM by DRepBRo.
Re: Extrusion flow
March 09, 2013 09:19AM
Do you have any pictures of the results?
That makes it easier to see what is going on.
May also want to try Slic3r or Kisslicer, settings are a little easier out of the box.
Re: Extrusion flow
March 09, 2013 11:12AM
Thanks for responding. Unfortunately I only have a phone camera so the image quality is very bad. Nonetheless, something can be seen. It's the first layer of the front panel of Black Nightmare Puzzle Box ~ ( The irony ! ). I've added comments for the outer perimeter flow, the infill is also obviously very bad.

I have checked the X axis movement as I mentioned above- didn't find problems. I calibrated the E steps / mm, so that I get the length I requested - but in SkeinForge or Slic3r I have to crank up the flow rate or else barely anything gets extruded. The print in the picture was sliced with Slic3r; I had to up the extrusion multiplier at 1.9. Layer height is 0.35 + 130% for the 1st layer. I would like to use Slic3r but I get better prints with SkeinForge.
open | download - 20130309035.jpg (289.4 KB)
Re: Extrusion flow
March 11, 2013 03:10PM
Since I started this thread, I will post an update on the issue. Well, I guess I never get to choose how to learn something - I eventually just get there taking only the bumpiest of all possible paths. So I found out I didn't secure the big extrusion gear with the small bearing that holds it firm. That's it.
Re: Extrusion flow
March 21, 2013 08:28AM
It sounds to me like the stepper driver is incorrectly set for the extruder. If you have the amps turned up too much the driver will shut down for a short time so it can recover and can be a very short cycle that is hard to notice. This will give you a pulsed output that will result in a lowered filament output like you are describing. The same can happen if the stepper driver gets too hot due to overload. Has it got a heat-sink and a fan to keep it cool?
Re: Extrusion flow
March 21, 2013 01:42PM
Thank you for replying. The issue is resolved now. Like I mentioned in my previous update, I didn't build the big extruding gear mechanism properly. The small bearing wasn't in place to keep the big gear steady enough. Once I installed the small bearing the plastic flow became consistent.
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