Filament chasing nozzle during skirt and first layer

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Filament chasing nozzle during skirt and first layer

Postby WalrusBrigade » 2016-Jul-Thu-14-Jul

Hello all,

I have tried to search for this issue on the forum, and while I'm sure someone is going to point out something I missed I haven't found my issue yet.

It is a problem with the first layer, but not a typical problem. While printing the skirt for my part (simple test part to get calibration right) the nozzle will often catch some of the filament from the first skirt loop as it starts the second skirt loop. This filament sticks to the nozzle, dragging the filament and ruining future skirts.

The problem persists during the first layer of the print, and even subsequent layers although the effects are different. For later layers if there is curling then the nozzle will dislodge the print. For the first layer what will happen is that the filament will stick to the nozzle, pulling up part of the first layer, creating a height increase that will hit the nozzle on the next pass and the problem will continue. I have included a picture and a link to a video of this happening.

I have tried a variety of print speeds, and have tried to fix my Z-offset but I think those settings are fine. The problem is, basically, that my nozzle catches any imperfections in a layer, which sticks to the nozzle and chases the nozzle movement.

Any help would be appreciated. I have a pretty solid 3D printing history, but almost exclusively on Makerbots.

I am using a Printrbot Metal Simple with a heated bed. I am using blue filament from printrbot with values of 1.75 mm for the diameter and a nozzle of 0.4 mm.

The current settings I have are below:
Cura Version 15.06
Print speed: 10 mm/s
Hot End Temp: 195 C
Bed Temp: 60 C
Skirt Lines: 3
Travel Speed: 70 mm/s

I also have included some gcode to prime and clean the nozzle before the print. The code basically prints a fat line of filament at the end of the board then retracts a bit and starts the print. That code is below, as well as the picture and a link to a youtube video showing an example of this problem.

Code: Select all
G90
G28                         ; Home all axes.
G29                         ; Auto-level the bed.
G0 X0 Y0 Z0.15 F9000        ; Move to the front-left part of the bed.
M109 S{print_temperature}   ; Set and wait for extruder temperature.
G92 E0                      ; Zero the extruder.
G1 X50 E25 F500             ; Extrude a fat line of filament to prime and clean the nozzle.
G92 E0                      ; Zero the extruder.
G1 E-1 F500                 ; Retract 1 mm.
G1 X80 F9000                ; Sweep right to cut any strings.
; Begin printing.


video of print: https://youtu.be/gpynkKPbMGg
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WalrusBrigade
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Filament chasing nozzle during skirt and first layer

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Re: Filament chasing nozzle during skirt and first layer

Postby Mooselake » 2016-Jul-Thu-14-Jul

I looks like that first layer isn't quite squished into the bed; try lowering your offset in 0.05mm steps and see if it improves.

Make sure that kapton surface is clean, then clean it again. IPA (isopropyl alcohol, not tasty adult beverage), denatured alcohol, acetone (don't spill that on your keyboard), or similar finger grease removing solvent.

Clean off the bottom of the nozzle while it's hot; I use a nylon scrub pad (actually a pad/sponge since Mrs. Moose buys them in big packs) to get it bright and shiny.

And perhaps an additional stick agent, like (ducks the flying hairspray) glue stick if the above isn't enough. Not completely necessary, I've successfully printed on a whole lotta stuff (kapton, PET, plain glass, sandblasted glass, hairspray, and more) but gluestick on glass has been reliable and the easiest to use and clean up. My aluminum bed is still in the box (gotta get to that some day) so I use glass on the heater PCB.

I like to raise the head about 50mm while priming, then grab the waste filament with a pair of needle nose pliers (or fingers if the pliers have escaped), never had very good luck with the prime and wipe technique.

Kirk
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Re: Filament chasing nozzle during skirt and first layer

Postby WalrusBrigade » 2016-Jul-Thu-14-Jul

Thanks for the tips. I'll try those and get back to you.
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Re: Filament chasing nozzle during skirt and first layer

Postby Mooselake » 2016-Jul-Thu-14-Jul

From watching the video it looks like a combination of insufficient squish and maybe not quite clean enough. Maybe try a nylon pad with a bit of solvent to both clean and just rough it up a bit, along with dropping the print head (with the offset) a bit.

You can embed a youtube video, it takes a specific format described in multiple copies of a sticky, and looks like this:



I fumbled fingered it the first time, but change rube to tube to make it work. No pun, or editorial comment about moose was intended. Note it's http, not the current googlian fad of https. No need to encrypt a publicly available video to the detriment of CPU cycles and bandwidth...

[yourube]http://www.youtube.com/watch?v=gpynkKPbMGg[/yourube]

Kirk
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Re: Filament chasing nozzle during skirt and first layer

Postby lairdb » 2016-Jul-Mon-14-Jul

Mooselake wrote:I looks like that first layer isn't quite squished into the bed; try lowering your offset in 0.05mm steps and see if it improves.


This, plus "Hairspray Changed My Life".

You need a good squish on that first layer, but even so and even with a heated bed, I wasn't able to get reliable and repeatable stick until I added hairspray to my Kapton. I was resistant, because I figured it would add a sticky mess, and most of why I got a heated bed was thinking I wouldn't need tape/gluestick/hairspray/juice/elf's tears/dragon sweat/etc., but once I broke down and tried it, I've never gone back.
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Re: Filament chasing nozzle during skirt and first layer

Postby Mooselake » 2016-Jul-Mon-21-Jul

Dragon sweat is best, as it's both heat resistant and sticky. However it's difficult to collect, and tends to tick off the dragon, so you need to learn how to train your dragon.

Glue stick works, and you can avoid dragon training and stressing out your sheep.

Kirk
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