... . It's fiendishly complex. For example the REA bridge chairs (L1) have a larger corner radius (1.3/4 ") than ordinary S1 chairs (which have 1" corner radius): 2_161458_330000001.png And GWR slide chairs have a full semi-circular end on the inside, for example. Templot does all the positioning and rotating of the chairs, and calculates where bridge chairs are needed to fit the space. For 3D printing it needs to be in the DXF file. So this is where I've got to: 2_161458_330000000.png Just the chair bases so far. The next job is to change the rails to a proper bullhead section. Then add the keys, and the chair jaws. And the chair screws. There is a lot still to do. I may be gone for some time. Just to be clear, the above wasn't drawn in a CAD program, it is the DXF export from Templot. The CAD program is used simply to view it, and then save it as an STL file for 3D printing. All the dimensions ...