As a member of the Winchester Railway Modellers on occasions I get asked for help or suggestions for other members projects.  The most recent came from our chairman who is building an OO gauge GWR layout and wants to build a route indicator box for a signal. Of course as he is a bit of signalling enthusiast and the layout would be controlled via mechanically interlocked lever frame the route indicator would have to work.  He sent me a rough sketch with some dimensions based on a standard GWR  pattern box with the question "any chance you could 3D print one of these?".

The whole indicator box will be about 10x9x4 millimetres and it needs to have 3 working indicator boards that slide up in to view as required.  I have a Wanhao duplicator 7 resin printer so it sounds as though it should be possible.  I knocked something together using my favourite CAD program, Designspark Mechanical, and attempted to print the complete box a a single entity.  It came out OK but I couldn't successfully clean out the uncured/semi-cured resin from the slots where the indicator boards were meant to slide. Back to the drawing board then...

Mark II was created from a kit of parts, a rear panel, a couple of dividers and a front panel.  Here's the parts as they came from the printer.  They are about 0.7mm thick at their thinnest and were printed directly on the print bed..

You can clearly see there is a ridge around the edge, rather like flash on a plastic moulding, which is caused by the first few layers being fired longer than the rest to bond the model to the build plate of the printer.  A couple of gentle passes with a small file easily removed the ridge but these parts a pretty delicate!

The pieces were bonded together as a sandwich with super glue (cynoacrylate).  I simply positioned the pieces the put a few spots of very thin blue along the outside edges. Capillary attraction was enough to draw the blue into the joins.  I then cleaned the assembly a bit more with a file then set about roughing out an indicator board to test it. A bit of work with some thin brass, a piercing saw and a file and something good enough for testing was obtained.

The pics below show the completed prototype.  A kit of parts will be posted off to Mr. Chairman for him to build the final model, mount it on a Dapol signal and figure out how to drive it with 3 servos!

Cheers

Dave