Ormerod2/original 0.5 nozzle/abs/burn on closed angles

Hello,

i'm pretty happy with my settings and hardware setup except one thing ..

everytime i print a "closed angled" surface i get abs burn on the layers ..

i've attached two pics of the problem, do you have any idea ?

Abs homemade
230C hotend
110C bed
Ormerod 0.5 nozzle
Simplify3d

Yes, that effect is very familiar to me! It happens on overhangs and is caused by curl-up. If you watch the print, you'll see that the edge or corner of the overhang starts to curl up just after the perimeter is printed, each layer curling up more and more. The nozzle hits the curl-up as it prints the following layer, with the side of the nozzle ploughing through the previous layer and creating the burnt effect (and a very uneven perimeter). If you are unlucky the nozzle does not manage to ride over the curl-up and causes the motor to skip, ruining the print.

To stop it happening you ideally need to have a separate print cooling fan directing cold air just below the nozzle - preferably only switched on when it prints the overhang. However, if you don't mind "babying" the print through the overhang there is a simple but crude method that I have often used when necessary and it works very well.

Orient the print on the build plate so the overhang is toward the front or side of the printer - get it reasonably close to the edge of the bed if you can. Now, during the entire time that the overhang layers are printing, get your head down to the level of the print and blow on the nozzle every time it comes around to printing the perimeters of the overhang. (Yes, it is a very boring job!). With ABS you need to do that whenever an overhang is more than about 30 degrees from vertical for more than 5 layers or so. It is extremely effective in preventing the curl-up and you can get perfect overhangs even up to as much as 60 degrees. Overhangs also benefit from setting the number of perimeters higher than usual - 3 or even 4 perimeters, and always print from inside out.

I've been planning on fitting a second fan and cooling ring for a while for that reason (there are some good designs available). One drawback though is that none of the slicing programs will control the fan in the way that is needed. It needs the air to be turned on only when the sections of perimeters at the overhang are being printed, but turned off for the rest of the layer. Leaving the fan on for the whole layer will cause weaker layer bonding. So unless I manually edit the G-code file (which is only worthwhile if I intend to print the item multiple times), I will still be babying the print, using a pushbutton to turn the fan on & off instead of my lungs.

I therefore try to avoid any overhang greater than 30 degrees on my own designs. When that is not possible, I will usually cut up the STL into different sections and print the item as several parts, each part oriented so there are no large overhangs, and then I bond the parts together afterwards using acetone.

Dave

Hi Dmould,

it's exactly this problem ^^

thanks for your advices, i will try to cool the zone with a fan, i've added a feature request for S3D regarding selective fan control but ... i doubt they will add this feature.