... print the chairs onto them? Is that a sensible idea, or have you just fallen off your chair laughing? Some progress with the coding, we now have the inner jaw finished with the insert in the rail web: 1. prototype rail dimensions: 2_260016_310000003.png 2. SMP rail to your dims: 2_260016_310000002.png Notice that the inner jaw insert is much less robust because of the thicker rail web, and the key is significantly deformed because of the excessive head depth. You can see that better on the end views: 2_260016_310000001.png 2_260016_300000000.png The SMP rail is significantly under scale width, the head is too deep, and the web is too thick. The deformed key which results and the weaker inner jaw is evident. It can't be beefed up much because of the need to clear wheel flanges. I assumed a fishing angle of 1:1.5 for the SMP rail, that's just a guess, but I doubt it matches the prototype 1:2.75 fishing angle. I suspect other model rail will be similarly compromised. What all this means is that I ...