The effect happens at corners, not overhang edges. The effect moves slowly from the corner to the whole outer edge but the problem is a corner issue. So at the tip of the gear teeth and the 2 corners of Aaron's overhang tests.
Yeah you are definitely correct, when I started this thread I hadn't spent as much time watching the output as I should have. The edges look fantastic, this machine is quite something.
That the inner border "repairs" the problem is fascinating - I hadn't noticed that - I guess maybe because I never went down to 5mm/sec? Don't you print inner shell before outer shell? Is it the next layer up inner border repairing the blob?
Yeah, the inner shell prints before the outer shell does on that same layer, and on the next layer up the inner border is repairing the blob. I think because the nozzle is spending more time at the corners during the inner boarder move, heating up the blob created on the outer boarder move, then it sticks to the nozzle and gets dragged back into the print.
The effect is cumulative as Aaron and I both mention so it's not surprising that it looks good for a while and then you start to see blobs. The effect is visible earlier but not until you get blobs does it really stand out.
Yeah, you can start to see very tiny lips the curl upwards form at the beginning of the print, for a couple of layers it looks like the layers are going to be smoothed out again, but the curling gets compounded until the curl disrupts the outer border.
Yes! One might think the effect would be smaller with smaller layers because the overlap is lessened (the layer above touches more of the layer below). And it is. Except the problem is cumulative and with thinner layers you have more layers for the problem to build up. So thinner layers can be better or worse... depending... on I'm not sure what.
Great point, yeah it's hard to see the effect happening in real time with thinner layers; but it's definitely a cumulative effect and not really apparent right away.
POSSIBLE CURA SOLUTIONS
1) move away. Inner overhang corners are fine. So if the nozzle could leave the corner moving away it might help. But you would need to do a retraction to avoid a string. Seems crazy. I don't think this would be good but it's a possible idea.
2) Print inner shell last. Maybe if the inner shell is printed second it will keep the corners from lifting. Unfortunately this might have to be done at 5mm/sec on the corner.
3) Non printing push down corner repair. After the outer shell is printed for a layer, the head could retract filament, and then revisit every corner printed on that layer and remelt it by hovering over each corner for some amount of time (.5 seconds?) or re-tracing the inner shell at 5mm/sec within 1mm of each corner?
4) Do option 2 but only slow to 5mm on every N layers. Maybe every 3rd layer is enough to keep the problem from getting serious.
Very interesting suggestions:
1. Do you mean, lift the head at the tip of a corner?
2. I'll take a look at Cura 13.04 and see if reversing the shell print makes a difference.
3. Yeah, the head would have to remelt and lift then you would have to press down rather quickly, I've tried to mend the corners right after the head moves over them with a metal rod but the plastic solidifies too fast and perhaps the metal rod wicks away heat too quickly. Maybe a warm metal rod?
4. I see what you mean here, every nth layer gets repaired so the cumulative effects don't build up.
I like your suggestions for the jerk and acceleration, I'll give them a try as well.
I'll report back my findings; what are your opinions on doing these tests on the overhang piece? I've modeled it so I don't have to wait for the entire bottom gear piece to print out, I was trying to find a quicker way to test different ideas out.
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gr5 2,157
A few things to note...
The effect happens at corners, not overhang edges. The effect moves slowly from the corner to the whole outer edge but the problem is a corner issue. So at the tip of the gear teeth and the 2 corners of Aaron's overhang tests.
That the inner border "repairs" the problem is fascinating - I hadn't noticed that - I guess maybe because I never went down to 5mm/sec? Don't you print inner shell before outer shell? Is it the next layer up inner border repairing the blob?
The effect is cumulative as Aaron and I both mention so it's not surprising that it looks good for a while and then you start to see blobs. The effect is visible earlier but not until you get blobs does it really stand out.
Yes! One might think the effect would be smaller with smaller layers because the overlap is lessened (the layer above touches more of the layer below). And it is. Except the problem is cumulative and with thinner layers you have more layers for the problem to build up. So thinner layers can be better or worse... depending... on I'm not sure what.
Great Stuff Aaron!
POSSIBLE CURA SOLUTIONS
1) move away. Inner overhang corners are fine. So if the nozzle could leave the corner moving away it might help. But you would need to do a retraction to avoid a string. Seems crazy. I don't think this would be good but it's a possible idea.
2) Print inner shell last. Maybe if the inner shell is printed second it will keep the corners from lifting. Unfortunately this might have to be done at 5mm/sec on the corner.
3) Non printing push down corner repair. After the outer shell is printed for a layer, the head could retract filament, and then revisit every corner printed on that layer and remelt it by hovering over each corner for some amount of time (.5 seconds?) or re-tracing the inner shell at 5mm/sec within 1mm of each corner?
4) Do option 2 but only slow to 5mm on every N layers. Maybe every 3rd layer is enough to keep the problem from getting serious.
One could test option 2 by setting the jerk speed to 3.5mm/sec which would mean the head would slow to 5mm at a 90 degree corner and then also set the acceleration to 37.5mm^3/sec (wow that's low!) it will still be under 10mm/sec 1mm away.
But again - the old cura, cura 13.04 let you choose the print order so you could do outer shell before inner shell:
http://software.ultimaker.com/old/
Maybe that alone would help. I'm pretty sure this "inner shell" pass that Aaron shows in the video is on the layer above - doing it on the same layer might help even more.
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