In anticipation of building my first routed wood track I have been using my 3D printer for many things. The latest gadget is a lane spacing jig that replaces the standard baseplate on my router and enables me to router, along with a 1/8" x 3/4" strip of Lexan in a previously routed lane slot, a perfect (ok, near perfect) second (and third) lane at 3 1/2" centre to centre spacing.

I posted the file on thingiverse.
If you want different lane spacing just pop the file into your favourite 3D design application and either add a solid flat ring or a "hole" ring to the existing object and modify your overall diameter.
Peter
I posted the file on thingiverse.
If you want different lane spacing just pop the file into your favourite 3D design application and either add a solid flat ring or a "hole" ring to the existing object and modify your overall diameter.
Peter
Comment