Help solving under extrusion

Hey there everyone...

I've been trying for months on and off to improve the prints form my Prusa Mendel IT2 RepRap.

Recently I've been able to print usable enough parts that I was able to start making enhancements to my printer, but I'm still dealing with some under-extrusion issues.

I just added a 40mm fan and fan duct, which focuses the air nicely, and an fine-tune adjustable Z-endstop which helped a great deal. I also improved things by adjusting the position of my filament spool to be up higher behind the printer, with the spool freely turning on metal Ikea table leg (round) – weird, but works somewhat. Seems to greatly reduce the tension on the filament I saw earlier.

I do see groups of layers that appear to be close to perfect (highlighted with the green overlay), and the rest look undersupplied with hot filament (in red).

I suspect I need to further reduce the tension on the filament, and am planning to use a 608 bearing insert for the spool.

I just wanted to get some eyes on this, and any other suggestions you all think I should be pursuing.

This skull was printed at 210c, heated bed at 60c. .35mm budaschnozzle, PLA (from Ultimachine)
0.2 mm Layer, speed at 40%

Thanks!

Edited 1 time(s). Last edit at 02/02/2015 12:43PM by jonkeegan.

What extruder setup do you have? If it's geared, what gearing.

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Please add your printer design to [reprap.org]

I'm using Wade's Accessible Extruder, using standard NEMA 17 motors.

Here's my Marlin config file:
[gist.github.com]

I used prusa's calculator to get the extruder settings, but possible i need to re-do these.
I think these are the key lines:
#define DEFAULT_AXIS_STEPS_PER_UNIT {80, 80, 3200/1.25,1400} // new settings for prusa it2
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 25} // (mm/sec)

Quote
jonkeegan
I'm using Wade's Accessible Extruder, using standard NEMA 17 motors.

Here's my Marlin config file:
[gist.github.com]

I used prusa's calculator to get the extruder settings, but possible i need to re-do these.
I think these are the key lines:
#define DEFAULT_AXIS_STEPS_PER_UNIT {80, 80, 3200/1.25,1400} // new settings for prusa it2
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 25} // (mm/sec)

What is the gear ratio of the gears you are using?

Are you using a direct motor or one with a gearbox?

What is effective diameter of hobbed bolt?

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Please add your printer design to [reprap.org]

This is my extruder: [www.thingiverse.com]

Think this is accurate (not at home right now)
gear Ratio: 43/10
pinch wheel: 8mm hobbed bolt. probably between 7-5 mm

Also looked at the formulas listed here; [reprap.org]