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coen

Struggling with 20mm boxes

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My ultimaker has been running for a while now, printing fluorescent green, after calibration of the steps per E setting with 20mm boxes giving great infill and quality. However, I always had problems with the bottom flaring out, and was not able to fix this.

I recently changed to transparent dark green PLA (3mm), which caused some problems:

IMG_0149.thumb.JPG.d09d27b35370b3e453f343b5b8754b35.JPG

Keeping the steps per E the same and just changing the measured diameter of the filament resulted in the bottom layer being too thick, so in the 2nd or 3rd layer there was so much plastic that the head would bump in to it and scar it.

Print settings are:

0,1mm layer height

0,8mm wall thickness

0,2mm bottom/top thickness

Fill 100%

skirt

150mm/s speed

225 C print temperature (PLA)

No support, no rafts, just simple 20mm boxes

Bottom layer speed 20mm/s

Initial layer thickness was originally at 0,2mm, later changed to 0 (same as normal layer)

Z-height was adjusted with the aluminum multimeter trick and http://www.thingiverse.com/thing:11033

Changing the initial layer thickness to 0 was the fix for the problem posted above.

However, before finding that out I thought the steps per E might be the problem, so I also lowered that 30%. After the first box was printed it was clear that infill was very far away from 100%, so I started printing more boxes to get the infill exactly right:

IMG_0151.thumb.JPG.b81dc8808be6e82a575404c1ab4fc712.JPG

The dark green ones are getting better and better infill. The last one however, is not completely filled, and is suffering from two other problems:

- the sides are starting to get 'wobbly'

- the bottom of the box is still flared (which all boxes suffer from)

IMG_0152.thumb.JPG.f709b3dbf1cf82c4561de23e9b669349.JPG

The last box actually has 30% more steps per E than the fluorescent green baseline setting.

Closeup:

IMG_0154.thumb.JPG.506ebbb440bbf3dca03619f2edaefdc0.JPG

Two questions remain to get my print quality better:

1. The knob I had found to fix the top infill (adjusting steps per E), has now been exhausted, because I start getting back other problems from it (the wobbly side). What is the correct approach to get a properly filled top?

2. The flared bottom is something I have not been able to change in any of the print. I tried the following:

- Adding some retraction at the start code (hypothesis: pressure buildup during raft/initial layer printing)

- Offsetting the z-height a little (setting +0,1mm to 0)

- printing at faster bottom speeds (ruined the print)

- Printing the bottom layer at the same thickness as the other layers

I get the feeling that the gcode does not account for the slower bottom speed, or that something else is going on. Has anyone seen this? What have you done to fix it?

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My solution to the flared bottom has been to print slower and with the bed slightly lower. You need to slow it down to give the deposition ample time to adhere to the surface before the printhead moves on. Basically, when running at the higher speed on the bottom layer, you have to press the deposition into the tape/printbed. Because the Z is not properly adjusted, it presses the excess material outward further than the slicer anticipates. This is also why you get the ridges on the surface fill that you can see very apparently in the middle square. If your bed is properly adjusted for the height the slicer anticipated (and your steps per e), you should rarely see those.

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What do your settings looks like?

I calibrated the z-height in this second instance by having an A4 below the printhead,and adjusting the z-end stop in such a way as to when it's I can feel a little friction when pulling the paper away (not totally free, and also not so much that you really have to use force to get it away).

I have now adjusted it in the start gcode to zero at 1=+0.1mm (which is also my layer height). So basically I have the thickness of a sheet of paper + 100 mu as the zero height when I start the print. Is this comparable to what you are doing?

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Honestly, my z height calibration is just a feel thing. I have my first layer printing at 18-20 mm/s. I turn the bed down to where it is just sticking at that speed. I also kind of know approximately how thick the lines should be. If it's too thin/not sticking well, I will turn the bed up in that area. If it's too fat, I'll turn it down slightly. Once I have it correct, it usually holds for ten or more prints.

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Wow, seems like your tip was right on. I used the printed z-adjustment screw to lower the bed a little bid (using the leveling screws seems kinda risky due to skewing the bed as well). And the flared bottom problem is gone.

Now I can actually see what my gcode was doing too... the z-height reset actually did nothing (trying to move the bed 1.6mm before the print didn't work. Besides, the retract I added at the start of the print is apparently only added after the raft has been printed, so it only resulted in the bottom layer of the print not getting any PLA. So all gcode reset to basic version and back to printing again!

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