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Extruding Problems on my Prusa i3

Posted by crenn 
Extruding Problems on my Prusa i3
September 14, 2015 09:25AM
Hi All,

I've got a Prusa i3 with a slight (understatement) grinding problem which is causing plenty of issue successfully printing. I'm attempting printing onto a 130c glass bed (which has worked well if the extruder behaves) using a J-Head nozzle I got a few years back. I got a 2nd hobbed bolt earlier this year thinking that was part of the reason the printing was failing, but similiar problems are occurring. Usually if I can get the printer going, it will do an ok print job (thin or missing parts of extruded lines), but at present the printer is grinding filament like no tomorrow.

-Pushing through filament fast, plenty of thin plastic noodles, rarely grinds
-During prints, extruder puts out a few blobs here and there, but not consistent. If I stop the print (usually on layer 2), there is a nice grind mark and plenty of plastic dust to show
-When extruding, the gears are moving smoothly, but I have noticed the 608z bearing is not always moving. The bearing is in place with a piece of 8mm threaded rod, not smooth rod. I don't have smooth rod to replace it
-Usually use dual springs on each 4mm bolt and have tried to tigthen it excessively and only just, with no success remedying the issue.

Prusa i3 with Aluminium frame
Polulu A4988 Black Stepper Motor Drivers
Arduino Mega (1280) with RAMPS 1.4 Shield (10A polyfuse removed and replaced with a short)
PCB Heated bed (Cannot remember the part number/version apart from it needing 12V)
850W Chinese ATX Power Supply (Came from a computer that couldn't use it)
J-Head 3mm filament extruder nozzle in a peek insulator, fishbone wades extruder block (http://www.thingiverse.com/thing:18379)

Any ideas on how to fix this issue?
Re: Extruding Problems on my Prusa i3
September 14, 2015 01:26PM
Ok ,let's start from the beginning...
There was a big band and the universer came into existence.
A bit later, oh, wait, wrong topic, sorry...
Start over...
First rectify if the problem originates with the extruder or the hotend.
I'll start from the bottom:
Assuming a thin nozzle, the common problem with the classic J-head is the inner teflon liner.
Telfon starts to soften around 200°C and printing a lot in ABS can weaken the liner.
As a result it can slip down into the nozzle part and decrease the inner diameter - jamming and hard extrusion.
Best remedy is to replace the liner with a new one.

For the extruder:
A smooth rod is always better for the bearing than a threaded one, the diameter is not right.
If you don't have on cut the smooth part off a long 8mm bolt, check the hardware section and you will find the long ones without a complete thread.
Next is to check that the filament actually moves freely through the extruder - especially eith the filament roll near the end the filament with the extrusion marks loves to get stuck in the lower bit.
If in doubt drill all holes for the filament to 4mm - or to the filament that matches the outside diameter of your teflon liner.
This way, if the filament makes too much trouble you can add a teflon liner winking smiley
I never really liked this types of extruder as the printed bearing mounts (IMHO) don't always offer the support required.
On the ones I tried the biggest problem was that a spacer was required for the bearings, otherwise they would grind on the plastic of the extruder.
I simply printed a ring 16mm outside, 13mm inside so the bearing outer ring would rest against the extruder but not the inner, spinning part.
Re: Extruding Problems on my Prusa i3
September 15, 2015 09:55AM
Just to update, I switched out the threaded rod for a bit of smooth rod (first time using the grinding disc dremel attachment) and it seems to have made extruding very consistent. There was also another piece of the puzzle, the bed was too low resulting in the filament not being able to be pushed through, resulting in grinding, so I've been able to print to a degree. Unfortunately it seems I still have issues, which either extruder calibration, or slic3r is not pushing enough filament through in the gcode. Not getting a solid base when printing objects. I ran out of time tonight, but got a good starting point for tomorrow.

Thanks for the help Downunder35m smiling smiley
Re: Extruding Problems on my Prusa i3
September 15, 2015 11:35AM
To get good bed adhesion, make sure that the first layer extrusion width (multiplier) is above 100%. I have mine at 160%, so it will extrude 60% more plastic on the first layer then normal.

Master Tinkerer
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