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jsamuels

Flared bottom on prints?

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Hi guys – new Ultimaker owner, and I’m having some issues with my prints. The bottom several layers of my prints are flared pretty heavily, so much so as to be unusable without some tedious hand-finish work. There’s also a groove in the side of the prints where the nozzle makes the movement between the inner and outer layers of the perimeter. I took some photos which shows the problem:

http://i.imgur.com/VTuMI.jpg

http://i.imgur.com/ZFNxw.jpg

These objects are sliced with the default settings in Cura and printed using Printrun, I haven't played with the advanced settings yet but I think I should be getting better quality.

Things I have tried:

I leveled the bed using a dial indicator, as best as I can – it’s within the flatness of the acrylic build platform at least.

I measured & set the filament diameter – roundness is quite good, while diameter varies only a bit from 2.79-2.81 mm; I used 2.80 as the average.

I zeroed the bed using a fine-adjust Z axis limit, a .0005” (.012mm) feeler gage fits with slight interference, while a .0015” is very snug and deflects the bed slightly. I did this in the center of the bed where objects are printed as there is some irregularity in the bed flatness, a “potato chip” shape if you will. But unless I’ve done something wrong, the center of the bed is flat and zeroed.

I checked the extruder steps per mm as per the first-run wizard, and it’s quite close, within a few mm. I didn’t alter it from the default value.

I adjusted the Z-axis zero, if I raise the nozzle higher on the bed it’s improved a bit but I can’t raise it very much or the parts won’t stick, even with 2 layers of blue tape.

I’ve also tried temperatures from 190-210, printing speeds from 30-75mm, and two different batches of filament. Cooler and slower has some improvement, but it’s not perfect.

Deleted/reinstalled Cura, and tried it on a 2nd machine (both are Win7 64bit). Same result.

I also note that objects are undersize – the 20mm calibration cube is ~19mm on the upper layers, and an M3 screw / nut won’t fit in the holes per the design:

http://www.thingiverse.com/thing:24809

Is it possible somehow I’m not getting enough plastic extruded past the first few layers somehow?

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Did you level the bed with a cold or hot nozzle? the nozzle slightly expands when heated up, and thus sits lower. This could mean your bed is actually too high which explains the flared bottom layers.

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My first thought would be the difference in speed between the first layer and your subsequent layers. Running at a slower speed increases the chances of sticking but also lays down a fatter line of material than higher speeds. Have you tried either slowing your print speed during the upper layers or upping your print speed during your initial layer?

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Thanks for the replies.

Daid: I leveled the bed while cold, and zeroed the Z axis while hot (after running a few prints actually). The tip of the nozzle is barely touching the bed. I can feel slight interference with a .0005" feeler gage. I'm not sure how to get it any more exact? BTW - it would be nice to have Z-axis compensation in your Cura software, instead of fiddling with a screw.

MSURunner it's a good thought. I'm not sure how it might account for this effect as the higher speed above the bottom layers should also extrude more plastic? I can test it though.

I will test these suggestions this evening, and report back. Thanks!

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I believe it does to an extent... Have you changed any of your speeds though? When I bumped mine up was when I started noticing this more. Flowrates aren't dynamically changed based upon speed as far as I can tell (Daid, please correct me if I'm wrong). For instance, if your printer slows down towards the top of a conical shaped part because of minimum layer time, the flow remains the same, thus you get a thicker line there again. The reverse is also true in my experience. But, that could just be my experience.

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Flowrate is an old term which we should no longer use because we have step-extruders. If you are seeing "speed related extrusion difference" you could have an extruder drive that is slipping, or you are printing too hot, causing oozing during printing.

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OK, I have adjusted Z axis, to where I can barely get adhesion to the printed bed. I've changed the initial layer to .2 mm, and lowered the temperature to 195. I added 5 skirt lines to hopefully work out any issues with the first plastic coming from the nozzle, and lowered infill and infill overlap to 10% - though I now have gaps in between perimeter and infill, so I'll need to raise this back up.

I created a simple test part in TinkerCad, a 20mm disk 5mm thick, with 8mm 4mm and 3mm holes and printed quite a few of these as I performed each adjustment. The best result:

Thickness of the skirt is approximately .25 mm.

The part thickness is 4.95 to 5.00 mm; the edges are slightly curled, making them thinner than the center.

The bottom flared area measures 19.95 to 20.05 mm.

The straight area on the sides measure 19.65-19.75 mm.

Also, the holes are undersized, but I understand this is likely due to the low poly count on the circles combined with thermal shrink. I don't have pin gauges handy to get an exact diameter, but I'm unable to fit an M4 screw (OD = 3.9mm) into the 4mm hole, nor will an M3 screw (OD = 2.9mm) fit into the 3mm hole without threading them in. They cannot be easily threaded into or through the bottom due to the flared ridge (which exists inside the holes as well).

Here are a few images:

First layer printing :

http://i.imgur.com/VETPo.jpg

Bottom of the object:

http://i.imgur.com/xD4HR.jpg

Side view of the object:

http://i.imgur.com/VxucU.jpg

It's obviously improved, but still a quite obvious ridge. I'm still not happy with it... I will keep tweaking though I'm not really sure what else to try just yet.

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