Horizontal lines

Hi there,

I have had my Mendel90 for some time now and gotten over all the major hurdles but the layers in the side of my prints have always been slightly bumpy. I mostly print mechanical parts so it isn't much of an issue but some parts I would like to look slightly better. I have done some looking and no suggestion I have found has made much difference. The part below is this http://www.thingiverse.com/thing:33974 from Thingiverse printed with a layer height of 0.19mm, 30% infill and a brim (don't worry about the bottom, it's just my poor clean up) it took 1:24 to complete and I used white Faberdashery PLA filament. Sliced using slic3r, g-code attached. My printer has an E3D V6 after my J-head got clogged with cheap filament and the print cooling fan is working but is set to run more slowly otherwise the hotend can't stay at 210^oC while printing but it is otherwise stock. I'm open to any suggestions to improve print quality.

Thanks.

Edited 1 time(s). Last edit at 02/28/2016 01:35PM by lexman26.

Looks like something severely wrong with the Z axis. Are the couplings well centred?

Also check that it is actually resting on both nuts. Sometimes the bed levelling procedure can leave it resting on just one and then it stick / slips at that other end giving very uneven layer increments.

The model isn't the best for looking for errors because it is a wavy distorted version of a building. I thought at first your print was much worse as I expected the roof to be straight, etc. Something more geometrical would be a better test.

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[www.hydraraptor.blogspot.com]

The brass nuts don't seem to be completely sung inside of the X motor bracket and X idler blocks. It makes sense because I reprinted them following the change to the way that the X axis smooth rods were clamped so my prints then could be at fault. I will re-print them again to make sure the nuts are snug and re-assemble. In the mean time here is a geometrical 20mm dice.

Thanks.

If the protruding lines go all the way around and are spaced about 1mm apart then it is definitely something wrong with the Z axis.

If they are not regularly spaced it could be filament that changes in diameter or perhaps the bed is flexing as it turns on and off. Try switching the bed off half way through the build. The part will probably detach before the end but if you get a smooth patch before that it would indicate bed flex.

If they go in at one side but out at the other, i.e. shifted laterally, then there is problem with the XY motion such as loose belts or the hot end is loose or maybe the z bearings are loose.

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[www.hydraraptor.blogspot.com]

Hey Nophead, so I reprinted the two main parts of the X axis and the brass nuts couldn't be tighter. The '2nd Dice' files are what I printed straight after I reassembled it, the '3rd Dice' is the one that I turned off the bed exactly 50% through the print. The 2nd dice is very similar in print quality to the first but the ridges are a little bit smoother and less pronounced. The ridges match up on all 3 dice with the 3rd having an additional line through the middle where I turned off the bed. I also wanted to show you how the texture and location of lines change based on the Z cross profile of the layer, it can be seen under the dots on the dice where the layers protrude more but is far more visible on the top of the X motor bracket part that I printed (photo was before installation). Turning off the bed didn't really affect print quality, my rebuilt helped slightly and I don't think my extruder is loose or my Faberdashery filament off. Any other things I can try?

Thanks.

It seems that your Z axis doesn't move equal amounts for each layer.

Which version of the Z couplings do you have, the original ones with PVC tubing or the newer ones with neoprene?

Are they well centred or do the threaded rods gyrate?

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[www.hydraraptor.blogspot.com]

I do have the old Z couplings with PVC and I haven't touched them since I built the printer. The threaded rods do seem to gyrate but I didn't think that was an issue due to the smooth rods holding the X axis in place, maybe replace the threaded rods? Would this explain the different texture based on the layer it is printing?

It's OK for the top of the threaded rods to wobble due to them being slightly bent but the bottoms must be well centred in the couplings. Otherwise I think as they rotate the spiral thread contacts at different places in the nut and that causes unequal layer height increments, especially near the bottom. When the layer height is too small the layer bulges all the way around and you get a ridge every 1mm.

It isn't an issue displacing the X axis unless your bearings are loose in the X ends. That can be fixed by wrapping them in tape. It doesn't create ridges all the way round though, the whole layer would be displaced in one direction, so I don't think that is your problem.

I am not sure what you mean by different textures but thin layers tends to come out more matt and thicker layers more glossy.

I changed to neoprene tubing when I discovered the hole was not very central in PVC tubing. It is also more elastic whereas the PVC deforms permanently. At the same time I moved the nut to the top X ends to reduce the effect of any eccentricity. I never saw anything as bad as yours though and it was very regular and definitely reduced with height. I could measure it with a dial gauge and I tried lots of alternative coupling designs before setting on the neoprene version that closes fully. The PVC ones could be closed too tight and crush the tubing asymmetrically.

It is also important to orientate the couplings so the flat on the shaft is pointing to one of the gaps. That minimised the eccentricity. Ideally the Z motors would not have flats.

PM me I can send you some new couplings and the neoprene tubing. I think they work more reliably whereas the PVC ones are a bit hit and miss. In the mean time you could try releasing them and re-centring them if they are indeed eccentric.

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[www.hydraraptor.blogspot.com]