HELP..."waves" happen on flat surface print for 4 months

Hello All,

This is my first post on this forum, I'm glad I found this place and willing to join the group.

Okay...I have a FF CreatorX and using Skeinforge+ReplicatorG for slicing
I started printing this piece 4 months ago, about 210x100 mm
however the "waving" unflatness keep happening on where it suppose to be completely flat (plz see attach images, focus on the red circle I drew)
I met a FF engineer and he suggests that I should change Edge Width over Height under Carve to 2.4.
Although the change did brought me 2 successful prints without the wave from over 30 failures ...
today the strange things happen again and I didn't change any setting from last success at all!

I use PLA, print temp 200,
no matter how I change the temp for both extruder or hot bed, the waving still there.
whats more, they happened almost on the same spot over prints and prints!

Edited 1 time(s). Last edit at 02/24/2015 07:35PM by tutu7931.

Hi tutu

My first thought was that the layer below is thicker where the wave occurs. If the head moves over the thicker thread, with a constant extrusion, then the thread gets wider => wave.
Why is the thread below thicker?....
- Filament with changing diameter? Tried you to use another Filament?
- Extruder not thight enough so it has too little grip.
- Filament roll not turning easily so the extruder must tie really hard?

But then you say "almost at the same spot".
Is your Bed uneven? Take something with a really flat corner and hold that onto the bed. Then check against a bright light if you see "waves".
Maybe your axis rods are compromised. Check them also for flatness. Ok, a bit difficult with your case. A flashlight maybe?

Interesting: I got exactly the same effect when I printed a test object that was just a large tray with a base that was only two layers thick. I have never seen it on any other object and never took the time to investigate it. I think it happens on the second layer of other large objects but gets covered over, so doesn't matter.

Also, I think I have only seen it on one of my machines, which has different mechanics, extruder, electronics, firmware and host to most of my other machines. I think the only thing I have in common with @tutu7931is Skeinforge but the waves look very similar.

I will do a few experiments to see if I can find the cause.

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[www.hydraraptor.blogspot.com]

What size nozzle are you using?

My best guess is the cross section you are extruding is too big for the nozzle size and the filament is being compressed lengthways instead of being stretched. It tends to become unstable and squirms, like pushing a string instead of pulling it.

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[www.hydraraptor.blogspot.com]

Another theory is the waves correspond to where your bed is a bit higher and the first layer flow rate is 100%. Where the bed is higher there is too much plastic and nowhere for it to go but sideways as it is laying down the first layer infill lines. When it comes back the other way there is already plastic where it wants to lay it and because the infill lines are long it has hardened. So instead of the nozzle ploughing through it it gets lifted a bit. It then lays down a line a bit higher than it should be. When it does the next line the hardened plastic lifts the nozzle and copies the waves in the previous line.

Basically when there is a bit too much plastic on the first layer it normally gets ploughed into ruts by the nozzle but when the object has a large base area the plastic is hard enough to lift the nozzle rather than the nozzle ploughing through it. So the excess plastic is deposited in waves due to the nozzle following the profile of the previous infill line. As soon as the nozzle lifts it releases some pressure and so deposits the excess plastic at that point again.

Edited 1 time(s). Last edit at 03/08/2015 04:57PM by nophead.

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[www.hydraraptor.blogspot.com]

Thanks for all your reply

It is really. really, really strange.
After over 50 times printing of the same model, the waving shape never happen to me again.
I didn't change filament, setting and all that.

Strange.