You may already be familiar with the problem of belt slippage on 3D printers. If your belts are too loose, or are worn, or maybe your motor doesn’t get enough current, you’ll start skipping steps. Then you end up with prints that go all slantyways across the offending axis, and that makes for not very useful prints. Belt wear and slippage used to be a recurring problem with the old pulley-and-line belts used in the first instar of my Printrbot Simple, but is less of a problem (but still sometimes a problem!) with the G2 timing belts that are now used.

But, that kind of slippage is usually consistant. Either it’s regularly back and forth for a wobbly appearance, or it’s a uniform slant as each layer is just a bit further off base than the one before. Sometimes it’s just one layer that skipped over a mm or two, but that’s enough to ruin your whole print.

A very odd sort of slippage started showing up on my printer recently. It’s a back-and-forth type, but I noticed on my second attempt to print the model, after I tightened my belts, that it was skipping back and forth at more or less the same layers.

After much troubleshooting, including switching slicing engines and host computers, I finally narrowed down the problem as mechanical in nature. It turns out that it wasn’t a loose belt, but a loose set screw on the pulley for the x-axis. The assembly instructions clearly call for Threadlocker Blue to be used on each of the set screws, as the vibration of the printer will shake them loose over time. I must have missed the threadlocker on this one screw because it didn’t have any crud on it when I pulled it out. I put it back in, with threadlocker, made it very, very tight, and then gave it some time to cure. Things are now printing straight, so problem solved!