Blackboard compass

thingiverse

This compass is designed specifically for use on a blackboard. I typically employ only a string as a compass on the blackboard, but this approach becomes impractical when the circle arc grows too large or when drawing full circles. This model features a central hole (which may be used to center the compass accurately or to pass something through and secure it in place). A crosshair is also present to ensure that the center of the circle is precisely located, and there is a recess for gluing a magnet (more practical for full circles or arcs with a very large radius). I utilized a magnet with a central hole so that visibility remains excellent even when positioning the compass. A clip is used to adjust the length of the string. The Openscad file is included, allowing you to modify the dimensions according to your string's size, magnet, and/or the central hole.