Compact Compass

thingiverse

I got the idea for this project from John Heisz's recent video on his YouTube channel, which you can find at https://ibuildit.ca/tips/making-a-compact-compass/. He also shows the tool in action. I thought it was a pretty clever design, so I decided to try making a 3D model suitable for printing. It probably would have been quicker to make one of these out of wood or metal than to write the OpenSCAD script and several test prints before I was happy with the result. Mine is basically his design except I set the dimension so the max radius is 10 cm and added a scale with markings from 1 to 10 cm. It also has an extra nub for the center pin. I'm not sure this is actually needed; John's seem to do just fine without it. I've uploaded the script in case you'd like to play with the sizes and shapes. The placement of the markers is in the module on line 47: ```javascript module markers(Rarm) { linear_extrude(Th) { for(i=[1:10]) { rotate([0,0,180-marker_angle(10*i,Rarm)]) translate([Rpiv, 0]) { rotate([0,0,180]) circle(2.5, $fn=3); translate([1.5,0]) square([3,4.4], true); } } translate([Rpiv, 0]) square([3,2]); } } ``` The $fn=3 term is how you coerce the circle command to give you a polygon, in this case a triangle. The marker_angle() function computes a rotation angle based on the arm radius parameter and the step size (10 mm) times the index variable i. That one uses a little trig to get the job done. ```javascript function marker_angle(x,r)=2*acos(x/(2*r)); ``` If you wanted an Imperial measurements version, it's pretty easy to modify the code. For a max size of 4" with gradients every 1/2", change Rarm to `4*25.4/2` at the top of the code and replace `10*i` with `i*25.4/2`. You'd also need to change the iterations in the for loop from 10 to 8 or you will get errors. Once printed, you can assemble it with a #6 machine screw and wingnut. I think it will work with M4 hardware as well, but I don't have any handy at the moment. You might have to adjust the machine_screw() sizes or ream it out a bit. Thanks for looking, Bob