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Incomplete layers

Posted by clogs51 
Incomplete layers
December 29, 2016 11:17PM
I have converted my I3 chinese aurora printer to bowden extruder,using "schlotts" extruder.Mk.7 drive gear.
e3d type hotend,0.4mm nozzle,1.75mm Esun grey PLA filament.@ 190 degrees C.
I have a severe extrusion problem,which is shown in the pic below:

As you can see,there already is a slight gap between the lines of the 5mm brim.As the actual print starts,things rapidly decline.
Gaps between the lines,and then a complete failure of extrusion.Not a blockage,as extrusion resumes,then after a few lines,fails again.
I have attempted to remedy this by doing the following:
Made sure the stepper driver was set at 4.5v.retest,fail.
disassembled and cleaned the hotend and nozzle.retest,fail.
Disassembled extruder,tightened bearing against filament.retest,fail
When testing filament feed out of bowden tube,20mm extrusion is exactly right at 20mm.
Tested belts,all ok.
Set sli3er to default settings.Slowed default accelleration to 300.retest,fail.
I,ve exhausted my limited knowledge,and am lost as to resolving this problem
I'm trying to print parts to finish my Hypercube build,but I need this printer to make the parts.

Edited 1 time(s). Last edit at 12/29/2016 11:17PM by clogs51.
Re: Incomplete layers
December 30, 2016 01:13AM
Do you have a nozzle fan? Heat creep can partially block nozzles resulting in under extrusion. If you have a fan, try turning it on for the whole duration of the print (first layer included).

Also try slowing the print down heavily (e.g. 20mm/s for infill and perimeters) and see what that does to the print quality.

If none of the above help, I'd try using a different filament as a test if you have it. Sometimes you get a bad spool that can't be cured.
Re: Incomplete layers
December 30, 2016 04:23AM
i had a similar problem a while ago, the hot end was coming loose as it heated up
Re: Incomplete layers
December 30, 2016 08:04AM
Is there any filament residue in your mk7 gear? I had the same problems with a hobbed bold. By cleaning all the tiny teeth with a scalpel knife I solved the problem.
Re: Incomplete layers
December 30, 2016 10:29AM

Made sure the stepper driver was set at 4.5v.retest,fail.
Did you mean 4.5V? What stepper driver would require that Vref, and for how much motor current?
Re: Incomplete layers
December 30, 2016 03:31PM
Brain fade.I meant 0.45.
Re: Incomplete layers
December 31, 2016 12:20AM
I am an idiot.I am an idiot.I am an idiot!
Did I say I was an idiot?
I have the printer on an old desk,which has a slightly bowed top.
So i put the printer on a piece of MDF.(medium density fibre board) to make sure it sits level.
Said piece of MDF had moved backwards,trapping the filament spool against the wall.
This must have caused the lack of extrusion at seemingly random points.
Once there was enough pressure on the roll,i presume it moved for a bit,until it got trapped again.
I also reset sli3er to default settings,which work ok for my setup.I only slowed the fill setting to 50mm/sec(default 70).
I now get very nice prints,much better than with the previous Wade's geared extruder setup.
Thank you all for your help,and a Happy New Year!

Edited 1 time(s). Last edit at 12/31/2016 12:21AM by clogs51.
Re: Incomplete layers
January 05, 2017 01:10AM
Hmm,I may still be an idiot,but for a different reason than mentioned above.
The day after I got really nice prints,it all turned to custard again.The nozzle would block after the first layer,I would clean it out,and start again.
This must have happened 4 or 5 times,before I'd had enough.
I left it for a couple of days,churning things over in my tiny mind.
Then I remembered I had changed the nozzle for a different one,after yet another clog.
I'm using a chinese e3d knock off,and the part of the standard nozzle that screws into the block is quite a bit longer than the nozzle i had fitted.
This meant there was a gap between the nozzle and the heatbreak.
I can only assume that gap filled up with molten filament,cooled,and caused a blockage.
I had a new spare hotend,so i robbed the nozzle from that,and hey presto,we're printing.
It's still not perfect,as I now have some gaps in outer layers,but I think this is a matter of extruder calibration,or maybe poor cooling.
I'll work on it some more.
New nozzles en route from aliexpress.
Re: Incomplete layers
January 05, 2017 02:49AM
The gap is most probably the cause, or WAS now you discovered it.

Usually I disassemble the hotend and counter the nozzle with the heatbrake and then screw the heatsink on the heatbrake. That way there's no gap.

Edited 1 time(s). Last edit at 01/05/2017 02:49AM by o_lampe.
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