

Trusting in Adam's forbearance; this is my Lion Class Boiler/Firebox/Smokebox unit. On the left (applied in OpenSCAD) are the knife edge supports on the bottom edges, which themselves are on a 'grid' to tie them together. It's very likely that the 'bottom' of the grid will be poorly formed, but as they're sacrificial that's OK. On the right is the veritable forest of fine Chitubox style 'grid' supports added by Blueprint Studio. In an ideal world these on their own would be sufficient for a successful print, but my 3D prints seem to have great difficulty in getting started accurately without assistance. The 'assisted' boiler print in my humble Anycubic Photon Mono 4K, was very accurately printed, a huge advance on the unassisted version produced on a more state of the art Elegoo Saturn with Chitubox 'grid' supports before I could do my own 3D printing. The Elegoo print had better surfaces (probably due to having Anti-Aliasing that actually works), but neither the dangling cylinder fronts nor firebox sides were where they should have been.
The grid and knife edge supports stay on for washing and curing, keeping everything aligned nicely, but they do need to be placed so that they can be safely and easily removed post-curing. Usually this involves cutting grid members and snapping off the now free to rotate knife edges by scoring and bending. As an aside it's only now dawned on me that we have two varieties of 'grid' supports causing some confusion - an 'actual' grid (frame?) and point supports 'on a grid' - alternative terminology needed!


Of course some prints don't need a 'frame', just the knife edge supports to start any 'bottom' edges accurately as with my two faced Lion Class buffer unit. For a brake van end I'd add the knife edges under the 'bottom' edge of any verandah tops and see if the point supports when added would then be sufficient to get those started OK. On my Beattie tender I employed knife edge supports to keep the buffer beam and footplate straight, and a row of knife edge supports on a frame to form the axlebox retainers in a nice straight line, none of which could be achieved (on an Elegoo printer with Chitubox supports) without them. In this case the fairly random point supports were created by Lychee Slicer before I had moved over to Blueprint Studio. The idea of knife edge supports was not mine*, and where I found out about them correctly attributed on one of my other threads.
[Edit] *It was Paul Sterling and his project 65033:
https://www.rmweb.co.uk/forums/topic/164432-project-65033-a-3d-printed-lner-j21/?do=findComment&comment=4438911