Color becomes darker in some layers

[adenovirux 0]

Hello,

The color of my prints changes from layer to layer. Usually the first darker layer appears in around 0.5cm above the bed, and may last for three layer, etc, and becomes normal. Then after certain layers, this phemenon happens again. Each time/layer the degree of darken varies. And no matter what kind of objects or PLA filaments I tried, it just happens. I supposed it is a temperature problem, so I played with printing tmeperature and minimal layer time. But it doesn't work. Anybody has an idea?

Thank you very much!

Here is a photo:

http://flic.kr/p/isVsMd

adenovirux

 

[IRobertI 521]

That's weird. Does it really happen with any PLA? I'm thinking that it could be the infill showing through on slightly translucent plastic. Do you have a picture of a more plain object, like a box? I think that would help in diagnosing what's happening.

To rule out wild temperature fluctuations you could watch the temperature during the print and see if it remains stable. Both cura and Pronterface can give you a temperature graph if you use them to print if you don't want to stare at the ulticontroller during the print.

 

[gr5 2,234]

I have heard 100 problems on this forum and this one seems new. At first I thought maybe temperature but you said "different PLA filaments" and *most* PLA colors are not temperature sensitive (a few are).

So I don't think it's temperature. Also you said it seems to happen 5mm off the bed every time. This makes me think it is related to the Z height. Maybe your screw threads aren't equal. Or maybe the Z axis gets stuck a little. This kind of thing happens a lot. So maybe the "darker" layers are closer together than normal (over extruded) or maybe they are farther apart (under extruded). Either could cause the layers to be darker.

Could you post pictures of other objects? Does this only happen on transparent colors?

 

[adenovirux 0]

Hi, there:

Here is the new photo. http://flic.kr/p/ith2xx

Both of them are PLA. The gold is not transparent, while the green is.

As you can see:

1. Similiar shape tend to has similiar pattern of darkeness (as the deers), but not necessary(the frogs).

2. The layer of darkeness varies a lot (compare the lower neck, middle, neck, the chin and the mouth of the deers).

3. The degree of darkeness also varies a lot (the one on dog's leg is of super dark!)

@ IRobertl: the temperature fulcturation in general happens only within the first 5-10 min, with the variation less than 3-5 deg. But for the small objects like these, which take 20min - 1hr, to the large objects, which takes 3hr to print, almost none of them can be escape from this effect.

I will print a square with another color later.

@ gr5: If it is the unequalness of Z-axis movement that cause the over and under extrusion, does it also means the outer contours will be slightly wider or smaller? But I feel quiet smooth....

Also if it is the case I should see the general darken effect once lowering down the layer thickness, right? But, as the middle frog and the left frog, which have a 0.2mm and a 0.1mm thickness seperately the degree of green is the same in their "normal" parts.....So I am wondering what is the real problem.

But how can I test the z-axis? I did unintentionally spray the sewing oil on Z-axis and caused a disaster - the oil dry up and clog within the screw. However, I used tooth brush and WD-40 to clean it up and now it works smooth and quiet.

Thank you for debuging with me! I have been bothered for a long time.

 

[gr5 2,234]

I am thiking more now that this is a Z screw issue. Did you put the green grease on the screw? Every UM1 and UM2 comes with a small plastic tube of green grease. Put one drop on there and move the Z platform up and down 4 times to spread the grease.

The problem isn't how *thick* the layers are - the problem is overextrusion versus underextrusion. You can simulate this by increasing flow to 150% for a few layers and then changing flow to 75% for a few layers and see if you get the same color changes.

If the Z stage is TOLD to move .2mm but it actually moves .15mm then you will get overextrusion. If later you tell it to move .2mm but it actually moves .25mm then you get underextrusion (not enough plastic to fill the space).

 

[chelys 0]

Maybe the problem is related to the use of the transparent filament. The transparency could be influenced by the speed and by the temperature of the extruder. Try to use a "solid" filament and check if the problem persist.

Whoops, I've not read that gold filament is not transparent...

[xeno 108]

I had the same happen, and while the print is smooth it shows these darker bands,

and I think it was caused by (very) minor temperature fluctuations,

when the cooling fan is a bit obstructed during the print, and not blow as much air around the print head.

and only shows itself with this particular silver PLA I Have

it looks a bit the same when I cast polyurethane resins with added silver or aluminum powder, you always get these lighter and darker bands, in swirly patters that show the flowing of the resin.

this is also caused by not stirring the two components properly, and the resin not curing (heating) evenly.

 

[adenovirux 0]

@ gr5: It was the green grease that has caused the disaster. After about 3 weeks of putting that on the Z-axsi, it became brown powderlized clog attached on the rod. That’s why I had to use the tooth brush and WD-40 to remove and dissolve the deposition, as well as re-lubricate the screw, otherwise a lots of noise had been generated during the z direction movement. I am wondering what the ingredient of green grease is and what the material of the z-axis rod is? Maybe the z-rod material serves as a catalyst for this chemical reaction because the green grease works very well for the x and y rod.

@ Xeno: I saw a lot of prints from thinkgiverse, many of that are not in good printing conditions but none of that shows this kind of problem, so I am wondering probably the temperature fluctuation is tolerable. But you mention the unevenness of mixing the resin and the colorant, etc. which reminds me the possibility of mixing some unwanted elements during the manufacture process. May I ask do you still smell an ill odor during printing process or not? If ABS is 100% then PLA is around 40% of the bad odor in my print, regardless the difference of the odors. It is not the case of Makerbot machine and filaments, where I was almost not able to smell anything significant when putting my nose close to the nozzle.

p.s. your model is awesome!

 

[illuminarti 18]

I don't know what happened to the green grease on your z-screw. That same grease has been used on UM1's and UM2's for years, and I've not heard anyone else complain of the same thing.

Note however that the green grease is NOT intended to be used on the the x and y rods. Use sewing machine oil for those. The grease is too thick, and will attract dirt and generally make a mess.

 

[gr5 2,234]

The smell should be like any PLA printing machine. Almost no smell compared to ABS. And the smell should be pleasant - like popcorn but not as strong.

 

[adenovirux 0]

I replace the hotend nozzle after 8 month of usage and even though it is still usable. I also change the filament to white-transparent and of course Cura (it's printing quality is much better than v13.11, though I haven't reach the best setting). Happily, it seems the situation of uneven darken color have disappeared, or at least temporary, if it is not the case where the white-transparent filament is not obvious for presenting the effect.

Here is the old nozzle:

http://flic.kr/p/iA76BU

http://flic.kr/p/iA6TVZ

Does it look normal? With red oxidized brass and dirty burned-like material on it?

But there is still some “dirty spots” even after 5 hr of printing. This phenomenon had also happened quiet often:

http://flic.kr/p/iA7DAn

Does anybody have an idea on what going on?

I guess it comes from the leakage through the junction between hotend isolator tube and the nozzle, to the outer part of the nozzle, and then to the print. Am I right?

After changing the nozzle the smell becomes better, but still not as pleasant as popcorn. Well, like *brown sugar* will be acceptable as this case…

I use only sewing oil now!