[Prusa i3] Too much extrusion, only on edges

[hernejj]

Thanks a lot for your answers !

I'm having two opposite adivces here haha !

I'm currently printing at 180 for the extruder and 85 for the bed. I think the bed may be a little hotter than necessary, i'll try printing something at 75.
I will also try to significantly increase the extrusion temperature, just to see what's going on, but it seems completely at the opposite of what printbus what saying, that is layers don't have time to cool down before the next layer is made. I'll try anyway, PLA is cheap
...

Yes, I see that Printbus is very knowledgeable on the subject of 3d printing. He has helped me with many problems. I do not mean to contradict his advice at all. I'm just trying to point out my personal experience.

I use a 5" desk fan to cool my prints. With that much cooling (admittedly, it is overkill) they tend to pop off the heated glass about 20 minutes into printing. So when cooling I usually need to use blue painters tape as my surface. In any event, I have only seen a small improvement on my overhangs with cooling. The benefit really came when I increased print temps.

As far as bed temp, I am now running at 63 degrees. I find that when I use a higher bed temp my longer/flatter PLA parts tend to warp/curl up off the bed at the corners.

Final note: All printers and environments are different, My 63 will not be the same effective temperature as your 63. You will need to observe the results and make adjustments as needed, one way or the other.

[awanegenebayo]

This is the result of printing at 210 and 75:

IMG_20160501_140417.jpgIMG_20160501_140431.jpg
Il looks better, but still not what i reach for ^^

I'll tune the temperatures and check if it's any beter !

[printbus]

Yes, I see that Printbus is very knowledgeable on the subject of 3d printing. He has helped me with many problems. I do not mean to contradict his advice at all. I'm just trying to point out my personal experience...

It could be that we're both right. Depending on how the 180 correlates to an actual temperature, I agree that could be too low to be providing good adhesion to the layer below. On my printer, I don't think I can get good results with any of the PLA I have being printed that low. But I'll stand by my suggestion that your best prints will result from printing on layers that have fully hardened.

It could be that a desk fan doesn't provide a focused enough airflow for the small area it is needed. My first experimenting with airflow involved a can of compressed air. I was only printing a small extruder gear at the time, and was having issues getting a result that meshed smoothly with the large gear. I eventually realized the teeth were squishing around quite a bit as the nozzle moved. I ended up following nozzle around with the tube from the can of air, cooling off the print as it was printing the gear teeth. Not a full blast of air - just a light touch on the can trigger. Awanegenebayo, that could be another method to try as an experiment.

[printbus]

Back to add that there's another trick that I sometimes apply on overhangs. I try to be in the area when I know a print is getting to a tricky overhang, and have a metal blade like a putty knife handy. If I see a soft edge or the unsupported edge starting to curl up, I'll quickly and gently rest the metal blade on the curl to flatten it; touching the extruded filament with the cool metal pulls heat out of the filament and hardens it flat. Sure, this can be tricky depending how quickly the nozzle returns to that same area of the print, and too much pressure with the blade can compress the soft material that leads to other problems. But I figure it's worth a shot if I'm likely to have to scrap the print anyway.

I'm ready to do this even though I'm usually using my print cooler blower. Print coolers typically blow in air from one side. That means not all sides of the print will get the same cooling. Due to heat from the hot end, the part of a print downwind from the hot end can end up with less cooling effect. Edges that are in-line with the airflow direction get more airflow exposure than edges that are perpendicular to it.

[awanegenebayo]

Thank you very much for your help everyone!I managed to achieve some pretty good prints mostly by reducing print speed on small objects. I think you were right printbus, thanks a lot.I think i will still install a cooling fan, to see if i get better results. I'll keep you updated if you want.I stumbled upon another problem lately : when printing small objects, the extruder tends to clog, it did twice in a row yesterday printing a small figurine with a lot of support material. I think i may be printing support material too fast, what do you think?

[printbus]

... I think i may be printing support material too fast, what do you think?

Hard to say. You haven't shared your support settings. We don't know what you have for a hot end. We don't know what you have for an extruder scheme. We don't have a link to a specific product page where we could figure out what you have there for a printer.

For me, extrusion stopping has typically been from being too aggressive with retraction settings. I have a hobbed bolt extruder scheme, and aggressive retraction can cause the same area of filament to roll back and forth on the knife edges of the hobbed bolt, simply causing the filament to be carved away...