After trying out pretty much every setting to escape the warping in the corners I focused on trying out an acrylic build platform instead. It seems like makerbotters and reprappers like it cause the ABS plastic sticks pretty good to it. The result was actually great. Although I found out that my X and Y axis wasn't square, but hey, you cant have everything. So follow me to the acrylic world...
The reason for trying a acrylic build platform is that I had some big trouble with warping as you can see below. I have tried with different amounts of adhesive paint and calibrated and adjusted to nozzle height. The large prints allways curled up around the edges. And yes I´m using ABS plastic.
|This plastic is just put onto the acrylic to show the warping, it was not printed on this.|
I lasercut some acrylic that would fit the build platform, this was standard 3mm and 2mm acrylic. The reason I wanted to try the 2mm was that it would probably had transferred the heat better from below. It didn't hold up to the forces though.
First try was to screw a acrylic plate onto the build plate without making any new holes around it, this meant that I only used the two holes for attaching the plate to the heater and then taping down the edges. I must say I underestimated to forces of warping. My 3mm acrylic just bent up and later snapped due to the forces.
Second try was to use the 4 holes in the corners to hold it down better while the plastic cooled. This worked out really good, I´m now able to print a 115x95x20mm print without it curling up in the edges. It really bites down to the acrylic platform.
|Don't forget to countersink those screws so that the nozzle bumps into them.|
I had another problem although that I think was the result of my ball bearing breaking in the middle of a print causing the machine to scream with a horrible sound. After this the prints are skewed, due to that the X and Y axis angle isn't 90 degrees to each other. Going to try to fix that later.
What was learned:
Make an acrylic platform if you need to print large prints or something that needs to stick really hard onto the platform. It's a lot more hassle to remove it from the platform but in some cases it might be worth it, it prints great.
Here´s the SVG file for laser cutting a platform for the UP! printer.