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revjb

Odd print defects on RHS of prints

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Hey Guys,

I have been having a small problem with my Ultimaker 2 and i was wondering if you could offer some assistance.

Quick background, got the machine last week done a couple of test prints but i have run into a small issue.

Overall the prints have been great and i have been majorly impressed but i have noticed a small issue. On the right hand side of the prints there occasionally crops up an issue in areas that require support..or building out from the edge.

I first noticed it on the Ultimaker robot default file, the right hand 'ear cup' has some flaws.

Image 1 - Left ear, fine: http://imgur.com/N9khP4Z,Dp2AhfN#0

Image 2 - Right ear, not fine: http://imgur.com/N9khP4Z,Dp2AhfN#1

I assumed this may be an issue with the file (silly me) but when i started another model today.

Here are some WIP that shows the same defect creeping in.

Album showing problem: http://imgur.com/a/Uyy48

As you can see the left most fin is perfect, crisp clean line but the others have a slight wibbly section. I am unsure how to proceed, being relatively inexperienced. I thought maybe supports might help but then having one fin fine seems to go against that logic.

Having finished the model i can highlight the defects in more details. Pictures in this album: http://imgur.com/a/AK6mU

As you can see in the first two images the bit at the top of the fins (printed first as upside down) there appears to be a major issue that is not present on the other fin. We also see some excess flash and almost laddering on parts of the vertical structure. Observation during printing showed that this excess was in the place where the printhead stopped and started (i.e. it would do a loop around and the start/stop point of the loop would have the notch on the side)

I am using standard settings:

PLA 2.8mm

0.1mm layer height

0.8mm shell thickness

0.6 Bottom/Top Thickness

15% Fill

50mm/s print speed

5 sec minimal layer time

cooling fan

nozzle temp 210C

Bed temp 70C

Any help would be greatly appreciated.

Also as a side, anyone have any amazing tips for bed levelling other than the eyeball/paper guess work method.

Many thanks.

Josh

 

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It's an issue with cooling - my machine does exactly the same thing. If you watch carefully while it is printing, the robot's right ear (left side as it faces you) will curl up on the first few layers, causing the issue.

You can try to minimize it by using the lowest heat setting that will extrude your PLA, setting the fans to 100%, and slowing the print speed. Replacing the metal fan shroud with a more effective printed one that doesn't leak cooling air can also help.

I've not been able to completely eliminate the issue on the robot yet.

 

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It's assymetric because the nozzle is to the left of the head and the right side doesn't get as much fan.

You can still print a perfect robot though.

lower print speed to 35mm/sec, lower bed temp to 60C (or even 50C but no lower than 45C as around 30C to 40C it stops sticking) and maybe possibly lower nozzle temp. 210C should be fine but maybe that particular PLA needs it a little cooler. Maybe 200C or even 190C. If you lower it too much you will get underextrusion. Every PLA color is a bit different in viscosity versus temp. Make sure min and max fan speeds are at 100%. Make sure fan comes on full by 1mm or so off table.

 

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Cool, thanks so far guys.

I am currently printing off another robot having altered a few settings.

Bed temp 50

Print temp 200

I also tried to alter the fan speeds but ran into issues, i couldn't find an obvious place to change it in Cura (14.07) but i may just be missing it, i have found the 'Tweak at Z 3.1.2' plugin and that seems to give the option of setting a new fan speed, so i se that to 'Z height to tweak, 1mm' and 'New Fan Speed, 255 (0-255 scale) but i noticed that according to the LED display the fan as still very low <25% up until around 5-10mm.

I have noticed during the first few stages that some of the edges are still curling up a little on the right (not on the hotbed, on top of the print) and some of the bridging looks maybe slightly worse than before.

I will post a picture or two when it has finished!

 

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You change the fan behaviour in the expert settings (Expert -> Open open expert settings...). By default the fans are set to come on gradually and reaching full speed at 5mm which matches what you're describing. I like to set it to 1mm.

As for those little bumps on the surface. Those are a slicer issue so there's not much you can do other than trying some other slicer. You can however try increasing the z-speed on the printer (which is done via the menu system on the printer) and slowing down the print speed and see if that helps.

 

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The dual extrusion readiness is at the same time the biggest problem with the UM2 IMHO. The smaller the diameter of your model the more you see it. Luckily once the (XY) diameter grows... say to 50mm the problems seem to disappear mostly... as the print heads move more over the target area + the layers have more time to cool. The issue manifests with angles also... because of the cooling issues the right side overhang always seem to come in different angle than the left side.

Personally I would like to "downgrade" my printhead to support only one nozzle so that the fans would be at equal distance from the business end of the hot end.

 

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for symmetrical models like that I also rotate the model on the bed facing the airflow - so at least they are the same.

This worked really well with the 3dhubs Marlin which used to have a strange eyelid on the right hand one (UM 1) until I rotated it - now they are the same.

James

 

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I also try to rotate the model in cura so that most of the overhangs are facing left. Most of my things unfortunately are cylindrical with overhangs going around the whole item. In these situations you see it most clearly by rotating the final piece and see the overhang angle vary 5-10 degrees.

 

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