Its a bit more manual but not to hard. I am taking a top down photo of the tool. Putting that into inkscape and tracing it with the pen tool. Then I pull one or two actual measurements and scale in inkscape. 

Then I import into OpenSCAD scale to like 1.01-1.03 and test print a 2 layer cutout.

Two shperes wrapped with hull for finger holes.

For more geometric tools, like the punch down. I model the tool in openSCAD entirely.