Whiteboard compass

thingiverse

This compass can be mounted on a whiteboard to draw precise arcs and circles. The supported radii range from 40 to 175 millimeters, with 5-millimeter detent intervals. Testing has not been conducted for the extra-long radius of 330 millimeters using two arms bolted together. Whiteboard markers ranging in diameter from 15 to 18 millimeters have undergone testing. A recommended STL file with supports and bed adhesion for the marker holder is available (disable supports/adhesion in your slicer). To install the arm, drill or tap an M5 or M6 into the base, or simply install a single M4 screw (the M4 should self-tap). Small slides for the marker holder may require minor filing or post-processing. For cheap suction cups, visit http://www.ebay.com/itm/50PCS-Clear-Transparent-Hanger-Kitchen-Bathroom-Suction-Cup-Sucker-20mm/311566424293?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649