Circular Things: Not So Circular

Recently, I found that circular things were not printing circularly. I also noticed that my infill was not connected to the perimeter in some cases and that my solid infill wasn't so solid. At first, I thought these things were not related. And to be honest, I thought the infill problems were a bug in slic3r because they were intermittent and happened only on certain models.

Tiny Toy Truck: The wheels are out of round and the solid fill isn't solid.

Notice the infill near the zig-zag perimeter. It doesn't connect.

I wasn't sure when this had started. I could remember printing circular things before and having them come out nicely. The first thing I did was to quickly start adjusting things. I played with my y rod mount figuring that since it was printing oval shaped things, my y axis must not be perpendicular to my x axis. I quickly found out that this wasn't going anywhere.

After a brief time of frustration, I decided I needed to be more analytical about it and create a model just for testing this problem. The model was simply a disc or coin shaped object that was 3 layers tall. I printed this with zero infill so I could just see how the perimeter turns out.

Note the two points in each circle. Also you can see from the blobbing that my extruder had some backlash which i talked about in my previous post.

The first thing I noticed after printing is that the circles weren't just out of round. They in fact each had a point in two distinct locations. So instantly I knew it wasn't a calibration issue. If I had a calibration issue, like inaccurate x/y steps or x/y axis not perpendicular to each other, the print would've still come out smooth. It would have just been out of round. This was starting to look like something was loose somewhere. I printed it a few more times and watched as it printed. It seemed that at each of the points is where the x axis was changing directions. I started hunting around the x axis looking for loose parts. I finally found that my x pulley's set screw wasn't holding the pulley to the motor shaft well enough. Such a simple problem can cause a lot of havoc in your prints. I tightened up the set screw and recalibrated my x/y steps. Voila! Perfect circles and solid infill. Nice.