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Solution to curling overhangs?

Posted by stoof 
Solution to curling overhangs?
October 23, 2012 01:33PM
I've always managed to get some really good prints out of my machine since I first started, but one problem I've always had to deal with was the overhangs curling. Whether I'm printing something with a semi cylinder overhangs such as this or a vertical hole, the edges of the over hang will tend to curl upwards and can ruin my print, either by making the print unstick from the bed or by causing my y-axis to lose steps, like in the picture attached.

I've tried adjusting the temperature, slowing the perimeter speed, cooling with a fan, adjusting the flow rate, pretty much every variable I can think of, and I still run into this problem very often. The only thing that reduces the overhang curling is increasing the layer height to be the same as the nozzle size (0.35), which makes some sense to me because the extrusion does not get squished or stressed on the layers. I would really like to be able to print overhangs at smaller layer heights though.

I'd appreciate any advice.
open | download - IMG_20121023_132005.jpg (278.3 KB)
Re: Solution to curling overhangs?
October 24, 2012 10:45PM
Are you printing in PLA? This problem has been haunting me from day one doing just that. I've heard that lowering the infill reduces the stress that causes the topsides to curl upwards, but I don't like how there's so much retraction during printing when my infill is too low (I use slic3r).

My solution was a brute force solution: use a stronger fan. Before a fan it was a crap shoot when it would curl and when it wouldn't, and my bridges were horrible, too. Adding a fan mount to my X carriage helped somewhat, and the first fan I used was a 5.62 CFM fan in 40mm and it improved things a lot. When I tried printing a stock T5 pully it would start curling upwards so I upgraded to a stronger fan. Anything larger than 40mm was a no-go for my set up because it would strike the frame, but I picked up a faster fan that now pumps out 11.3 CFM and it's been keeping things put for the most part. I did try a print recently that STILL curled upwards when it had overhang of a large angle (I would think it would droop downwards instead), but at least it didn't dislocate my hotend, knock the print off, or cause missed steps. I don't feel like this is a good solution, but I too am out of ideas.

Also, since I'm using Sanguinololu electronics, there's no [stock] fan control, so my beefier fan is always on, and it's fighting with my heated bed and making it difficult to keep the first layer from curling and lifting.

On my to-do list is upgrading my electronics to get PWM fan control, and replacing my extruder setup with something based around a geared stepper, probably Makergear's design: the wider Prusa with a gap to compensate for the extra size of the stepper. Once that's there with the wider profile, I can mount a larger sized fan. Delta actually makes a 40mm fan that shoots out 26.3 CFM, but it also makes 58 dB of noise! spinning smiley sticking its tongue out so I'd want to upgrade by fan size instead of making myself deaf.
Re: Solution to curling overhangs?
October 25, 2012 08:56AM
Mazaw Wrote:
> Also, since I'm using Sanguinololu electronics,
> there's no fan control, so my beefier fan is
> always on, and it's fighting with my heated bed
> and making it difficult to keep the first layer
> from curling and lifting.
> On my to-do list is upgrading my electronics to
> get PWM fan control,

I totally agree with Mazaw that fans are the solution to PLA curling.

However I'm not sure if Mazaw is aware but Sanguinololu CAN support fan control if you use firmware that has software PWM (e.g. repetier) and you can then just use a cheap transistor/MOSFET to switch the fan - works fine for me and totally worth the small effort given the benefits of slic3r-controlled fans. Slic3r's fan control settings allow you to use a large fan and vary the power as needed - a great solution to minimising curling whilst minimising layer delamination when fan cooling is not needed.
Re: Solution to curling overhangs?
October 25, 2012 07:09PM
Interesting, thanks for the advice.

Yes I am printing with PLA, sorry I forgot to mention it previously. I am using RAMPS 1.4 and have a small 40mm fan mounted to the x carriage with a fan shroud that points it towards the print. I use slic3r as well, now I wish there was a separate fan setting for doing overhangs as well. I do run the fan when I'm doing a lot of these prints, but maybe my fan is not strong enough. My bridging works phenomenally though. Also, I notice that the curling tends to start on corners then builds up gradually as the overhang gets steeper.

Just now a 5 hour print got ruined in the 4.5th hour due to this very issue angry smiley
Re: Solution to curling overhangs?
November 14, 2012 08:54AM
I know this thread is a little old now but I had teh same issues and have a prusa mendal running off of ramps 1.4 and marlin software. i had a 40mm fan with a nozzel and found that I was getting more air blowing on the heat be than the part. i printing a fan off of thingiverse that is called circular fan duct, I think. It is a ring that is mounted around the bottom part of the hotend and blows downward as a 50 something degree angle to the air is more focused on the specific area of your print instead of blowing it accross the part. i also realized that a fan mounted on any side will have some air blocked from when the air gets to the hot end. The big issue I have is that the lm8uu bearing holder I have accompanied with my j-head V-b bot end (short) is to tight for room. I just finished designing a new x-carrage that is wider and removed the mound on the ends to compensate for the extra length. That will buy me 20mm more room between the bearing holders. I am also designing a ducted fan like the one explained above that will fit my carrage nicley. I guess the point is, if you can get your air focused on the area you need to cool you will see an awsome improvement in bridging and overhangs (I also had HUG isssues with overhangs and the circular fan duct I am using was terribly hard to print becasue of that.)

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