... meant by gcode files being specific to a printer. As a matter of interest, attached is the gcode file generated by Templot for the 4mm scale BS-95R bullhead rail: 2_111752_390000002.jpg Don't try to use it on your printer, but you can load it into the preview simulator in Simplify3D to watch the process -- File> Preview G-Code File... menu item. Notice the half-keys being inserted into the rail web. The slab on the right is a purge-patch for the nozzle. 2_110807_280000000.png It won't escape your notice that I still have a long way to go, but I think I have at least proved the concept. I do now have the radio-control stuff to use in a test loco -- intended for the boat kit, I wonder which will get built first? cheers, Martin. p.s. all -- although this is a gcode file, it's not suitable for actual printing as it stands, unless you have a Bibo printer with a 0.6mm nozzle on the left, loaded with ...