Beginner: Cause of mess

Can anyone give me some advice on what would be causing the wiggly mess that is coming out of my prints? There doesn't seem to be any pattern to when it happens. Some prints are perfect and are others covered with it.

Also, the top of the octopus' head it is a little melted. I assume this is because the tiny area on the last few layers of the slice. I guess the way to combat this is to slow it down on these layers to allow more heat to be removed, I have tried playing with the cooling options in skienforge but it doesn't seem to make too much difference. What else should I look at?

Thanks in advance, Samuel

The wiggly lines are caused by the extruder stalling during retract. This seems to be due to the gears being meshed too closely, or possibly not lubricated. For me it happened on a machine where I knew the gears were a bit tight but it went away after two small prints.

As printed gears are never perfect there will be a worse case tooth combination where a high spot on one gear corresponds to one on the other. Since they have prime numbers of teeth that will only come round every 11 turns of the big gear and 39 of the little gear, which is about 250mm of filament.

I think the best way to set the motor position is to remove the hot end and manually pull that amount of filament through the extruder checking for binding. It needs to be done with filament in place and the springs tensioned because the hobbed bolt is 0.2mm smaller than the bearing so it gets pushed closer.

Edited 1 time(s). Last edit at 08/29/2013 11:46AM by nophead.

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[www.hydraraptor.blogspot.com]

I just tried that, I found a little bit of binding and positioned it so there is none now. I have also applied more grease.
But it has not fixed the problem. Any other ideas?

Are you printing from the SD card? It can also be caused if your PC pauses occasional if you are running over USB.

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[www.hydraraptor.blogspot.com]

Yep. SD card and monitor/watch off

You could try reducing the extruder acceleration in the firmware but I can't see why you would need to.

What diameter are the loopy bits and what layer height are you using?

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[www.hydraraptor.blogspot.com]

I'm printing 0.3 layer height. The loops seem to have a diameter just a little bit less than .3, its hard for me to tell as I don't have a micrometer and it is hard to tell on my callipers.

I was doing some really flat prints and I realised that the Z home point was off (.2mm), so I fixed it. I did another print and it still has the same loopy issue.
How do I turn down the extruder acceleration? Can I do it in skienforge?
Also, could the fact that the loops never happen in the top third where the gradient is toward the center be a clue to something?

cheesemunger Wrote:
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>.... How do I turn down the extruder acceleration? Can
> I do it in skienforge?

Tak a nosey at the (current) discussion thread here: [forums.reprap.org]

Alan

Tried halving the E acceleration, didn't work. Any more ideas?

If anyone cares the solution was new filament. It seems to be printing perfectly now.

cheesemunger Wrote:
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> If anyone cares the solution was new filament. It
> seems to be printing perfectly now.


That's interesting, care to share what the old filament was and where it came from?

The old filament was the sample that came the kit, I believe from Faberdashery. I hate to blame that, as I have only good things about it online, but as soon as I changed to a new filament and calibrated the prints were perfect.