Ugly print artifacts on modest overhangs

[drumrboy44 0]

I am getting really bad print quality issues on what I believe to be relatively modest overhangs. Typically I print at 0.1 mm layers, 50-70 mm/s print speed, 220 deg C, PLA on an UM1. I think I still have the default 5 seconds per layer overhang. The ukulele (which I have printed fully, successfully once and it is awesome ( http://www.thingiverse.com/thing:268090 ) is printed at 100% infill for strength. Even the frets, which barely overhang at all, print awfully.

 

 

The wine stopper picture below is an extremely modest "overhang" on the outer edge, and it too has the same issues (which look like strings, but I understand "stringing" to normally be used to describe a different problem.

What is likely causing this? I feel like my printer wasn't always so bad on such overhangs. Any suggestions on settings that can improve or eliminate this?

 

[gr5 1,663]

Print those at half speed and they should improve quite a bit. For highest quality I print at 20mm/sec. Here is a picture showing speed versus bumps quality that you speak of (on the pumpkin):

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/?p=24010

Regarding the 100% infill - I really don't recommend that. 50% infill is amazingly dense and leaves no room for the PLA to expand/shrink. How about trying 50% infill? It's very strong.

The bottom curve of the ukelele is always going to have overhang bumps for a few inches but that white piece you should be able to get perfect.

 

[gr5 1,663]

Also for overhangs, FAN IS CRITICAL. Make sure fans are at 100% by 1 or 2mm above print bed.

 

[drumrboy44 0]

Do you mean to manually ensure fan is at 100%, or is there some way I can ensure that in Cura? Also, I don't want to turn an already-18-hour-print into a 36 hour print. On the black ukulele base, you can see the overhang is only for the first inch or two. Would it work to just turn down flow rate percentage for that portion of the print manually, and then adjust to full speed for the less steep portions?

 

[gr5 1,663]

Do you mean to manually ensure fan is at 100%, or is there some way I can ensure that in Cura?

I mean make sure your fans work. Both of them. Also make sure in Cura they turn on gradually over the first, say 5 layers. So in Cura you could just set that easily.

Also, I don't want to turn an already-18-hour-print into a 36 hour print.

Well going to 50% infill will speed things up. You can have a fast infill speed and slow skin speed if you want but if you do that I would make the skin at least 3 layers thick both to keep the infill from showing through and also to give the speed change time to adjust.

Also you can control the print speed as it is printing so you could set it to print 50mm/sec in cura and then slow down to 50% print speed for the first - heavy overhang - area. The "print slower" is going to help that white part more than the ukelele itself. The ukelele didn't have many (any?) bumps as the overhang got more vertical than 45 anyway.

If you really want the ukelele to be strong, do it all in the shell - consider maybe 10 layers of shell (4mm) and then only 24% infill. That should be strong enough to stand on. Maybe.

Usually the strength is all in the outer layers. So for example when you see construction of structural things that need to be light weight they often drill holes in the center where it doesn't affect strength so much. Or like how plumbers and electricians are only supposed to drill holes in the *center* of studs and joists. Of course *some* infill will definitely make it stronger.

 

[gr5 1,663]

Wait - I just looked at the thingiverse model - I take it all back about infill. Yes 100% infill makes sense. I thought you were filling in the area that is normally "air" in a regular ukelele. I didn't know it was playable!

 

[gr5 1,663]

So don't change infill speed. To speed things up you can manually slow down the print on the overhang areas and the go back to 100% when things are more vertical.

 

[mnis 11]

By the way,

I do not know if it has already been said, or someone has already tried:

I have found that large overhangs are more successful when they are positioned on the build platform as possible to the machine's rear panel.

Placing, only the first two or three layers at the standard bed temperature (75 degrees). Then try it at 65-60 degrees to keep for the rest, which should work with a good bed-to-nozzle adjustment. Nevertheless, it may be difficult for objects with large contact surface without additional adhesive.

- If possible, use low printing temperatures object quality can generally improve.

- Print Extremely slow, with many and large overhangs.

- Very stable objects, already with 22-33 percent infill are possible.

- Objects with layers greater than 0.1 mm can also look very good. In any case, you can save with a little thicker layers selected a lot of time.

- Avoid drafts.

- Glass cleaner may adversely affect the adhesive properties of the glass.

Markus

[drumrboy44 0]

I printed at 35 mm/s instead of 60 or so, and that made all the difference. Ukulele sounds great, too!