Everything is OpenSCAD with help from Inkscape for the DXFs.

Ramp dimensions (main base - not including extra stuff on top) are 5cm high x 20cm long x 3cm wide. The slot in the ramp is 1.5cm wide x 0.5cm tall with a 0.5cm opening for the slider.

The slider piece sits on a base that is 1.3cm wide x 0.3 cm tall with a vertical piece 0.4cm wide. The whole piece is 2cm tall if I remember correctly. I'm not sure how much leeway is needed for it to slide smoothly so I tried to leave 1mm in either direction. Because of the size I imagine one of those army guys might fit right in there (the kind we used to torture with a magnifying glass).

The sphere is 4cm wide and could probably go bigger. It's mostly for illustration, any ball of similar size will work. I have a crystal sphere on my desk that I had in mind while I was creating the ramp.

Would appreciate any comments on the printability of the ramp. The slots are at a sharp angle but it's very small so I'm not sure. If not I have two easy solutions in mind.

Thanks to everyone out there making great tutorials!