Extruding Issues

Hi All,

Another day, another problem.

I have 3mm filament and a J-head Mk IV hot-end with a 1.75mm nozzle. I'm using a Greg's extruder with a bought hobbed bolt - M4 tap.

I was attempting to extrude some ABS on friday. I heated the hot end to 240ºC but the rate of extrusion was very slow, to the point where the hobbed bolt appeared to slip on the ABS and the plastic couldn't move. The plastic was a free sample, so I don't know whether it's just not of a great quality (?)

Anyway, I was wondering if anyone has had this issue or if anyone could suggest a fix? Also, whether I should try with PLA instead - is it easier to deal with?

Thanks!

Quote
RocketBoy87
I have 3mm filament and a J-head Mk IV hot-end with a 1.75mm nozzle.

Are you using 3mm filament with a hotend designed for 1.75mm filament?

That would be your problem right there.

Apologies - was a typo.

3mm filament with a 0.35mm nozzle orifice

You could try cleaning the nozzle hole with a fine piece of wire or 0.35 drill.

I have also found to clean it you can try using a bamboo skewer to push all the molten plastic out of the hotend and then push a new piece of filament in and remove it really quickly. This will usually pull any leftover filament out of the chamber with the contaminants.

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The J-head nozzles seem to work quite consistently from what I hear. Have you checked to see that the extruder thermistor is giving you the correct values?

I extrude ABS at 230 - 250 deg C depending on the feedrate.

You can also try tightening the idler springs by 1/2 turn until the hobbed bolt stops slipping. ABS needs to be squeezed into the teeth more than PLA does.

cool thanks for your suggestions. will give them a shot tomorrow!

OK, so I cleared the nozzle and tried again today. Still no extrusion. Only when I set the extruder temperature to 265ºC and I forced the filament through by hand did I get a little bit of extrusion...

So, either my thermistor is reading incorrectly or, could it be possible the batch of ABS I have has a higher melting point?

In another thread about extrusion problems in the general forum someone was having a similar issue and it was caused by over tightening the j-head nozzle or set screw in the top which caused the inner liner to compress and bulge down near the bottom and stop the filament from going through to the melt chamber.

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Thanks Sublime. The J-head came pre-assembled, but I'll try and loosen off the nozzle and see what happens.

Thanks sublime. That did the trick. I've printed my first cube! But in PLA. Another little question though. I attempted to print a few more cubes yesterday to see the affect of certain settings on Slic3r and for all about half way through the print (1cm^3) the extrusion became lumpy or didn't extrude at all. Any idea why?

Hard to say with out knowing which settings you changed.

A good starting point for a 0.35 nozzle would be:

0.35mm nozzle diameter
0.25 layer height
30mm/s perimeter (Marlin) 15mm/s (sprinter)
50mm/s infill (Marlin) 40mm/s (sprinter)
40mm/s solid infill (Marlin) 30mm/s (sprinter)
100mm/s travel (Marlin) 65mm/s (sprinter)
0.5-1.0mm retract at 25mm/s
195c (PLA Marlin) 190c (PLA sprinter)
First layer temp 5-10c hotter
Filament diameter = low average of measured diameter

Leave the rest alone. If the prints are not turning out the problems will most likely be mechanical or firmware calibration (E steps per mm).

Note: The temperatures and speeds should work well with 4043D PLA as well as good quality Chinese filament but that is hard to determine if this is your first machine. So if you are using Chinese filament and have a lot of problems it may be your issue.

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver

Lifesaver! Will try those settings over the weekend.