foehnsturm

Definitely more fun than the ice blade covers I did before :wink: Scaled to 80%, KISSlicer, UM original, 0.1 mm layer height, 7:45 h printing time, no post-processing

That's been my assumption as well. ("I looks like it is all about print speed and - indeed - cooling. Not about cooling down the part before the next layers starts, but immediate cooling in the moment of extrusion"). I think it makes sense to distinguish between intra-layer (e.g between first, second pass and infill) the and inter-layer cooling. The first causes problems with small islands, even on bigger parts while the latter is more important for small parts and for avoiding shrinkage and warping. Depending on the part geometry, one of the two issues will limit your printing speed.

I'm using a crossflow fan, which I think should provide sufficient cooling. Drilling up the brass piece should be feasible (by taking care of the minuscule nozzle thread), I'm not sure about the PTFE part.

I don't know, but I will give the http://merlin-hotend.de/ a try. Already ordered two (3 and 1,75 mm) for around 50 €. Besides the conventional heater block the main difference are the tiny airbrush nozzles it uses. On youtube there is a of a guy printing really clean gear wheels with it (in German)I will make a new aluminum top part on my lathe, so I can use the same mount and swap with the UBIS.

+1 for illuminartis explanation. It looks like this ridge formation is a tendency of FDM process per se. Caused by cohesion, adhesion, surface tension or a mixture of all. It only develops to a problem if the underlying structure isn't solid enough to hold back the extruded filament. And this the case when there are overhangs and / or the underlying structures are significantly reheated and softened, which is dependent on heat input = printing speed.

Looking at your first picture, does it take 4 sec to print the inner pass of these tiny rectangular structures? And does the Eiffel tower feature the tiny, slicer-generated re-enforcing infill at the lips? This is where everything begins (watching requires some patience): Slow motion: 2x

1) The retraction pause was not intended as an explanation for your issue. I just found it remarkable when watching the video. 2) and 3) The lip builds up as Dim3nsioneer explains. More or less regardless how long the layer time is: Nozzle arrives on a tiny area - heats it up - returns after a very short time (too short for enough temperature drop, in the video you can see what a difference 0.5 sec makes) for the second loop - further heating- "stirring" several layers underneath - picking up liquified parts by cohesion (which I can see in my video raw material) . Regarding the overhang edge, I like Dim3nsioneer's exlpanation: Why does it happen just on the overhang side? Well it doesn't. The effect is just stronger. You get the same thing everywhere if you print small structures too fast (e.g. minimum layer time below 5s EDIT: I think it's more time between perimeter/infill lines than layer time EDIT ). But on the overhang side the amount of material to be heated up again is limited or smaller compared to the other side. So the material temperature after contact with the nozzle is higher on the overhang side.

just doubled the value: the first time sitting and waiting for priming, the second time waiting for retraction.

at 50 mm/s it's approx. 0,3 sec sitting, waiting and cooking the part and 0,3 sec printing ...

@KitWasHere I ordered at RS components (Germany). Worldwide: http://www.rs-components.com

Another thought: You see the nozzle is sitting there, heating up the part and waiting for priming/retraction to be finished. This takes a considerable amount of time compared to the short printing time in-between. Faster retraction (higher speed and/or less distance) would be very helpful. Direct driven extruders should have an advantage here. As far as I remember, Meshmixer documentation somewhere mentions a very small support diameter as the Makerbot default (of course it will move and print slower as well).

Sometimes theory doesn't match reality so well :wink: I'm still evaluating and making closeup, slow motion videos. I looks like it is all about print speed and - indeed - cooling. Not about cooling down the part before the next layers starts, but immediate cooling in the moment of extrusion. The edges raise when the nozzle returns one or more times within the next fractions of a second and the spot is not cooled down enough. Most common scenario: Tiny supporting poles with 2 perimeter lines. After the first perimeter the nozzle comes back within a few tenths of a second to print the second perimeter. If there is considerable overhang, trouble is likely to follow. Is there that tiny supporting infill at the lips? A short video:

My experience is that the PLA/PHA stuff extrudes up to 50% faster. But with frequent retractions uniform extrusion is quite hard to achieve.

One thing I will check out, is nozzle shape. The UBIS I received today has a super sharp nozzle with almost no flat area. Eventually there is more room for the filament to "escape".

That's funny, what a coincidence! Today I thought about starting a topic on this, but didn't have the time: "The tiny leg issue" or "Meshmixer support worries" My understanding so far: - The extrusion process applies some pressure to the structure underneath - slanted structures, if tiny enough, sooner or later will bend due to that pressure - bending causes thicker extrusion, especialy on the most overhanging edges - ... - if structures are rigid enough, backpressure increases and things even out by themselves - if not, more bending, more thickened edges ... and finally the nozzle breaks down the structure or knocks it over Therapy: I don't have a clue ... Extrusion *has* to apply some pressure. Small structures *will* give in. Thinner layers should increase the problem as there is less room for the extruded filament and less clearance for the print head.

Finally my UBIS arrived today, looks like German customs is quite slow. Molex connectors are scheduled for tomorrow. Very curious about it ...

@Aaron Exactly! If I would have to design a printer I would start with your idea. It's the most straightforward approach to provide an optimum thermal situation.

Cool! How is the air flow distribution over the duct width?

Still work in progress, you may want to make some modifications (fan mount etc.) Here is a link to a http://foehnsturm.com/3dp/side-cover-crossflow.zip. No sure if it helps.

That's true. I'm using 50% duty cycle as the maximum now.

The key is a laminar airflow with some cm height which covers the entire printbed. You could achieve that with an axial fan and ducts as well, I assume. But I had less than encouraging experiences when I tried to produce that kind of airflow with axial fans and ducts (heavy airflow in the middle section and nothing at the sides) . It's a matter of how much static pressure the fan can handle as well. My choice was the crossflow fan because it is used in similar situations (ovens etc.) and the "output" is exactly as I need it.

My steppers are outside (direct drive) and the upper half of the print head and the bowden tube always receive plenty of fresh, cool air. But it requires http://umforum.ultimaker.com/index.php?/topic/3890-the-crossflow-fan-approach/?p=30643. I think there is no patent on the air curtain principle.

Yes, that's why I came to that conclusion. Having the whole piece at nearly the same temperature during the print really helps. No heated bed: uniform temp but considerable overall shrinking, low adhesion and high lift-off forces to fight with Heated bed: good adhesion but high temperature gradient within the part and partial shrinking causing the elephant foot Heated chamber: good adhesion and uniform temp, very low lift-off forces due to shrinking until the part cools down

My understanding is that the elephant foot is caused by a considerable temperature difference within a small area. While the bottom layers stay at heat bed temperature (and are constantly heated), the layers above are heavily cooled by the fans and therefore shrink. So, if the heat bed temp is too low, the part will lift of. If it is high enough the part will stick but has to give in within the zone near glass transition temp. This is why I don't have any issues any more since my "cooling" air is almost at the same temperature as the heat bed. Perhaps the main secret of a heated chamber.

I assume a thickness of 0.4 mm should work quite well. If not, two oscillating lines will do it. It might be visible, depending on wall thickness and material color, like the normal infill. The curve is an interesting question. I like the idea of having longer segments in touch with the perimeter and peaks facing inwards, like bracings. However the peaks should be printable without any risk due to the sharp corners.