1. What did you do?
I looked at the Assembler 1 animation.

2. What happened?
The Assembler 1 animation is not perfectly looped, some of the gears jump back/forward a bit when the animation restarts. Refer to the attached video, it can be seen when the metal I-beam in the top left reaches it's left ...

Really cool drills! But they have a small issue that i found with their model/hitbox. As you can see in the picture if you put 2 drills diagonally of one another, it seems like that there is enough space to squeak through, but that is not the case.