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poor print quality with prusa I2

Posted by n2Jesus 
poor print quality with prusa I2
September 23, 2015 12:52PM
Hi all,
I just finished building a mendel I2. I'm in the testing & tweaking stage now.

When I print, instead of extrusions that bond together I get individual lines that do not connect.
On a 3 perimeter print I can see blue tape between each perimeter extrusion. My solid infill looks like a basket weave instead of a solid print.

To me, it acts like I'm starving the extruder.
I have made sure that slic3r knows I'm using 1.75mm filament instead of 3mm.

I've tried increasing the flow rate to 150%. this hasn't helped much.
I increased the temp from 205C to 215C thinking it would help it flow better.

I'm about out of ideas. Would lowering temp help?

I'm using a .4mm nozzle printing in .3mm layers.

any input would be greatly appreciated.

Re: poor print quality with prusa I2
September 23, 2015 01:10PM
1. Is it just the first layer in which the perimeters don't bond, or all layers? If it's just the first layer then you don't have the Z=0 height set correctly.

2. Have you calibrated the extruder steps/mm?

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: poor print quality with prusa I2
September 23, 2015 02:05PM
I have calibrated, and my Z is set correctly.

Every layer has problems. A print eventually sticks together enough to maintain its form, but it looks horrible.

If perfect is Rembrandt, this is a toddler trying to copy it with chalk.

Something I just thought of...
My previous printer uses lead screws. How tight do the belts need to be to prevent backlash?
Re: poor print quality with prusa I2
September 23, 2015 02:56PM
A few thoughts:
1. Is the nozzle diameter correct? With a new nozzle you often find out that 0.3 is actually more like 0.35mm.
That means the calibrted extrusion is for a smaller diameter.
Filament always expands a bit when extruding but measure a string once cooled and if it is close to 0.5mm your nozzle might not be just 0.4mm.
Here it can help to check a print with the nozzle set to 0.45mm.

2. Feeding problems.
No, stay here, I did not mean you should get something to eat winking smiley
The cheap all metal hotends love to mess with the filament.
So double check the filament does not require excessive force to be pushed through the nozzle.

3. If the above is all ok try to lower the layer height.
You are pretty close to the limit for a proper print with your current layer height.
To bond on the sides the filament needs to be pushed onto the previous layer, which can be tricky if the layer is almost as heigh as it is wide.
Re: poor print quality with prusa I2
September 26, 2015 09:24AM

I finally got back to it. My extruded pla measured .52mm

I set the diameter up to .45mm and it helped a lot, but I think it could go even more.

how much does pla expand? is .45mm a good number, or should I go higher?

Re: poor print quality with prusa I2
September 29, 2015 08:09PM
Couple other things can sometimes cause this. Your filament might be smaller in diameter than what is in the slicer. If you have 1.75 in the slicer and the filament is actually averaging 1.6 you might get this. It helps to have a set of digital calipers/micrometer to measure the real diameter. Measure multiple spots and multiple angles.

Double check steps per mm extrusion. It may seem like a waste but go ahead and mark 10 cm or so as precisely as you can and then extrude 10 cm manually and make sure it hits the mark. Sometimes the teeth of the filament drive get filled and then the filament can start slipping a bit, so this is a good way to test your extruder without taking it apart to inspect the hobbed bolt.

Nozzle might be partially blocked. If you are using PLA it is pretty easy to get it to pull out at around 80 C or so and get it to all come out as one piece. Then look through the nozzle and make sure it is completely clean.

You might be trying to extrude too fast. Your extruder motor might skip steps when printing if it can't push plastic as fast as the print settings require. You could try slowing the print down to half speed and see what happens.
Re: poor print quality with prusa I2
September 29, 2015 09:27PM
In the slicer, check ALL of your extrusion widths, like infill, perimeter, and things like that. make sure that they are something logical.
smiling smiley

Master Tinkerer
Re: poor print quality with prusa I2
September 29, 2015 11:57PM
I had this exact problem with my i2 also.

After 12 months of trouble free printing, the extrusion started to get leaner and leaner (over the course of three or four projects), finally the prints would no longer hold together.

I removed and disassembled the J-head.

I found (molten) plastic had worked its way up behind the Teflon sleeve down by the hot end.

The sleeve had distorted enough to either-
a) provide friction to the infeed
b) (partially at first) block the nozzle.

or may have been a combination of both.

Would you like the steps to disassemble the J-head.. ? (Not really a big job, can be done with the tools supplied with the machine).

Edited 1 time(s). Last edit at 09/29/2015 11:57PM by buildit.
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