Fixing a cracked ABS print, part 1
The other day, I showed a pic of a print that had cracked quite late in the process.
The reason for ABS prints cracking is due to the temperature issues. Normally you get a lot of warping issues if you have poor print plate adhesion, but I am printing on BuildTak on a heated platform.
I also cheated and used helper disks on the print at the bottom, and I printed near one edge, so once the helper disks were completed, I put clamps around the heated print bed that clamped the helper disks to the bottom, so even if they would let go, it would prevent the base from warping.
It can, however result in the tension traveling upwards in your print, and that can create a crack. As in my case, a quite sever one that went through 1/3 of my printed piece.
The best way really to combat cracks and warping, is to put your 3D printer in an enclosure of some kind. My printer, the Makergear M2 that I’ve mentioned earlier in this blog, have a print bed that is moving on the Y-axis. This means that if you want to build an enclosure, it would have to be a rather large enclosure to allow the print bed to travel all the way back and forth.
I simply do not have that space at the moment.
So, I try and do what I can to combat the cracks in my print by tweaking numbers. Making thicker bottom layers to force the plastic into my build surface. Tweaking the extrusion multiplier to get enough plastic to create better layer adhesion. Working with different amount of perimeters on my print, and different types of infill patterns (and settings) to try and reduce these tensions.
I still have not come up with the perfect formula, but I do know that ABS plastic dissolves (quickly) in acetone!
So, I have in the past taken off parts that have shown the possibility of a crack and simply taken a paint brush and painted acetone on the surface. The surface will melt and blend together and create a chemical bond that is as strong as the material itself.
I have also taken filament remnants from an old roll, cut them in small pieces, placed it in a glass jar and added acetone to create a sticky goo that once it cures, it will once again be pure ABS.
THIS .. is my secret weapon for this.
I started by brushing the entire print with acetone. I made sure to get a little extra into that crack. I did not try and force the crack shut, that would only have create more tension in the model.
Instead, once the surface had started to set, I added some ABS goo to the model and tried and push as much inside the mode as I could in the crack, and then used a piece of a break blade knife to spread it out on the surface.
Now, this stuff melts the surface FAST, so there is no real time to do some fancy stuff here, as once it starts to dissolve the surface, you really need to stop working.
I went a little too far, but at the time it was really necessary. This is the result when I left it to cure.
Tomorrow when it is all cured, I will add another layer of goo into what is left of the crevice and once cured fully, I will sand the ankle, and it should be as strong as ever, and ready for a paint job!
