Saftey Compass (Parametric)

A compact tool for drawing circles and arcs. Sometimes called a “safety compass” (because it doesn't have the sharp point of a traditional compass), this is easy to print and use. I created it for the Drawing Templates contest, but wasn't able to submit it due to some printer issues before the deadline.

I uploaded STLs for two variants, one with radii at one sixteenth inch intervals and one with radii at two millimeter intervals - the imperial version is shown in the pictures.

The model uses OpenSCAD and is fully parametric, so it should be easy to adjust the size, available radii, or pen diameter. I recommend using a development snapshot of OpenSCAD with the “manifold” feature enabled for much faster rendering, but it will work in release versions too.

Usage

The compass has two parts: the “plate” (the large, triangular piece) and the “head” (the round, spinning part). There are three ways to use it:

1. For very small radii, trace the templates in the head
2. For small radii, hold the plate, insert a pen into one of the holes in the head, and rotate the head by moving the pen
3. For larger radii, hold the head, insert a pen into one of the holes in the plate, and rotate plate around the head by moving the pen

(It's also fun to play with as a fidget toy when you're not drawing circles) 

Printing

I printed in PETG for the flexibility and translucency, but it should work in PLA or other materials. You need to print one head and one plate. The plate comes in two variants:

• A version with the marking lines built-in. You can either print this in a single color or insert a color change right before the marking layer. Note that the clips will also be the marking color if you do this.
• A version with no marking lines, with the markings as a separate STL. Use this if you either don't want markings or if you have an MMU/AMS and want to print the markings in a different color.

The model is designed for a 0.2mm layer height. No other special print settings are required.

If you find the tolerances are too loose or too tight, I suggest adjusting them in the source file and then exporting new objects from OpenSCAD. Scaling the model in the slicer will mess up the radii values (but you might not care about this.)

While it should be possible to print in place, I recommend printing the plate and head separately (this also makes it easy to use different colors.) To assemble, insert the head into two of the clips and then flex the plate to snap in the third clip. The head should spin freely.