Poor ABS Print Quality

[Humpty 0]

Hey everyone.  I'm fairly new to 3D Printing adn have been loving it so far.  Started with PLA and everything has went well so I decide to give ABS a try.  

ABS is not going so well.  The print quality is turning out very poor, especially with overhangs.  I did a retraction test and got that sorted out, no stringing.  I also ran a bridge test and it turned out near perfect.  But some bridges on this recnt test I ran did not fair so well. All ABS prints the overhang is bad. I have an enclosure and have tried a bunch of different temps.  I run a slow speed of 40mm/s.  I need some advice on other things to test out to improve this print quality.  I've attached a few pics so you can see whats going on.

Any suggestions?

[gr5 1,270]

Are you using any fan?  It looks like you have the fan off.  what kind of printer is this?

 

ABS needs just a little bit of fan for overhangs and quality in general.  But too much fan and it will have bad adhesion and very poor strength along layer lines and might even split while printing along layer lines.

[Humpty 0]

The fan is used when doing bridges  I have edited the profile to have 10% fan speed but have not tested it yet.

I am using Anycubic Mega-S and Cura 4 Beta.  I've been printing at 250 degrees as the filament roll says 245-265, bed temp is 110.  No issues with first layer adhesion.

[gr5 1,270]

That looks like a marlin based printer.  That's good as I know Marlin well.

 

Well I would play with the fan.

 

You need fan for overhangs as well when printing ABS.  So basically you want it always on - but on low.

 

On some of my printers (but not all) 10% fan will not actually do anything - it won't spin the fan (on other printers it works fine).  But it's more complicated.

 

If I set the fan to 30% and lower it to 10% it's fine (usually).  And if the fan is off and I set it to 10% Marlin over powers the fan for 1/4 second and then drops to the programmed value.  Which is great.  But if I go to 2% and then 10%, it doesn't work.  And cura tends to do 1/5th of the fan for each layer until you get up to full requested fan (so if you request 10% it does 0% first layer, 2% second, 4%, 6%, and so on and for a few of my printers that means the fan NEVER turns on - well it turns on for 1/4 second when gcode requests 2% - but that's it).

 

Anyway assuming you do all these tests and the fan is definitely spinning, I would still consider increasing it a bit.  Play with the fan and listen to the sounds and run it at what sounds like half power (not half frequency - I think cooling power is proportional to rpm to the 3rd or 4th power).  Basically half as loud.

 

For all filaments - if overhangs or bridging is bad then increase the fan.

 

 

[Humpty 0]

OK so i tried a couple of the over hang tests.  With the fan at 10 it was trying to move but just twitching. When i set it to 20 it was working, man what a difference, got higher with the angles before they started getting worse and the front was just cleaner and nicer looking.  Overall the 20% made a huge difference. 

 

I did the overhang test at 230 and 30% fan.  looked good, but when i tried a normal print it wasn't hot enough and it ended up failing because the layers werent sticking together.  Im going to try a rpint at 250 and 20%/

 

Anyways thanks so much for the advice, you clearly know what you are doing.  You've been a big help.  Any other ABS advice you could give me that would save me hours of googling? lol