Overhang issue

Hi,

I just complete the assembly of my tricolour mendel. I've printed a few mono pieces, then finished the 2 extra extruders assembly and print the first 3 color print.

Now, i want to optimize the settings of my printer to get better print results. I use the standard 0.5 nozzle and 1.75 PLA.

In addition to the great assembly guide, i follow the instructions found in this thread reprap topic and i had amazing improvement. I think that tighten the belts (both X and Y) and the bed springs are very important, i was to gentle when i first build the printer...

Here is what i get now :

10*10*50 mm Tower, 0.3 layer height


22.5 * 22.5 * 10 thin wall (0.5 wall), 0.2 layer height


20 * 20 * 20 box, 0.2 layer hieght


and the faulty print, (honeycomb infill)


The issue is that the nozzle is pushing everything down (only on the overhang part) when adding a new layer on Y and worst, when the nozzle turns to X, it kind of pull on the stack of layer on the overhang. The first few layer are ok but it always ends up with the result you can see in the picture after being push and pull every layer. The overhang part seems too soft.

I try to print at 185° instead of 200° like in the picture, it seems to be a little better but it is far from what i think i could expect from this printer. It became fast annoying to print only vertical walls

Do you think an extra fan pointing at the print would be helpfull ? Maybe it will help to cool the layer so that the overhang is more solid when the hot nozzle come for the next layer.

I also had this same result on a much larger print (over 10 * 10 Cm). I print perimeters at 30 mm/s and small perimeters at 20 mm/s.

Any help to improve / solve this issue woul be appreciated.

Thanks and excuse my very bad english
Sebastien

Hello Seb,

Quote
seb_reunion

Do you think an extra fan pointing at the print would be helpfull ? Maybe it will help to cool the layer so that the overhang is more solid when the hot nozzle come for the next layer.

Absolutely, I would start by that.
What happens is the plastic is still hot and flexible when the hotend comes back to lay another layer on top of it, and as there is not enough material under to keep it flat the plastic is lifted and curls up.
Layer after layer this effect adds up and leads to your blob situation.
Blowing fan would make it cool down faster.

Another solution is to slow down the printer, but that sucks


Et au passage si tu es de la Réunion, il y a une partie francophone : [forums.reprap.org]

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

So I will definitely try to add a fan direct to my print.

I found this printed part. Do you think I can mount it on the fourth (and last) hot end slot available ? I already assembled the 3 hot ends on my tricolor mendel.

Is there a link anywhere to power this extra fan? Where can I plug this extra fan on my master / Slave board card so I can use the slicer settings regarding this fan (power after n layer) ?

Another question : I've no idea of the correct speed to use when printing such part with overhang.
Do you think my settings 30 mm/s for perimeter and 20 mm/s for small perimeter are alright or should I go under ? Is the speed function of the size of the print ?

Thx for your help.

Et effectivement, je suis de la réunion (au soleil avec 30° dans mon bureau avec la clim, peut être cela joue t il sur le refroidissement des couches), je manquerai pas de poster dans la section française Next time.

Thanks to you all.
Seb

Edited 3 time(s). Last edit at 03/28/2014 12:46PM by seb_reunion.

Overhangs are always a problem. It's not that the nozzle keeps pushing it down, it's that the overhanging portion keeps curling upward. A cooling fan definitely helps.

So I set up a cooling fan and it has been very helpful regarding the overhang issue.
I found the settings in slic3r to manage the cooling fan, I don't really understand how it is managed... I start it up manually.

I fitted a 0.3 nozzle because my large gear on the extruder became loose on the hex hole. I had extruding issue as the large gear didn't rotate the screw with the hobbed thing.

I temporary fix this and I will print another large gear.

Regarding the retraction parameters in slic3r, with a Bowden tube, what length seem OK (1 default but I still have some extra deposit just before the axe travel to the next position).

Thx

print with 0.3 nozzle, 0.2 layer height, 200° first / 185°, quite slow (i will try to print faster without loosing any quality sometime)

Here's the result of the printed large gear, i'm very pleased with the result :






I print the tapei 101 tower, scale so it goes 10 Cm height and the result is quite good, but not perfect. The bottom is quite perfect (except the 4 little round thing), the layers are good.





The problem comes from the top of the print. This antenna is exactly 1.4 mm wide (so quite thin) and the result is quite blobby...Even the part below this antenna is quite rough.
I think that the layer print time is too short for the layer to cool down before another one is added. Quite the same issue as in my first post regarding the overhang issue, only on quite smaller part of the print.

The fan beside the nozzle was full on, i even add another fan in front of the printer pointing toward the print.

Any idea to improve the quality on this very small detail ?? The only idea i've got is to try to reduce the temp to the minimum without stopping the extrusion...

Thx

Edited 1 time(s). Last edit at 04/01/2014 10:06AM by seb_reunion.

Nice results on the gear.
The fan can be software controlled if you plug it into your electronics (it is often plugged to the 2nd extruder heater connector, or have its own dedicated plug) and update your firmware settings to tell where it is plugged.


Regarding the tower's antenna, with such a little surface to print for the top, you should print multiple instance of the same part together.
Otherwise the PLA will never have the ability to cool down enough, even with a very slow speed and a fan, because the nozzle will always be around the same place and keeping it hot.
If you print multiples towers together the hotend will move from one to another, allowing the plastic to cool down between layers.

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

Hi DeuxVis,

Thanks for your advice, i will print multiple instance to let each layer cooling down. It seems to be the only way on such small parts.

I plugged my fan on my master board as it says in the reprap documentation. My question regarding the management of the fan was in fact related to slic3r. I do not understand why it keeps powering on / off the fan. As i print exclusively PLA for now, i just set the fan always on after the first layer.

FYI, i set the retraction lenght to 3mm, it seems to be better, nicer print. I read on slic3r website documentation that if your printer has a bowden tube, you could set the retraction up to 4 mm (1 default) due to the friction inside the tube.