Dave Holt
Western Thunderer
0.27 mm for Gibson medium (2 mm) knobs, according my trig.
However, there are two holes in the cab spectacle plate that locate the ends of the hand rail and these are much closer (approx 1.325 mm - I can just get a 1.1 mm drill bit between the hand rail wire and the boiler) to the boiler than the medium knob standout so I'm going to use Gibson shoulder-less knobs. The shank of these is 0.6 mm diameter, so the 0.65 mm holes I've already drilled are slightly oversize, but not enough to warrant plugging and re-drilling - just plenty of glue.
The drawback with these knobs is that they have no mounting flange (by design) but I've found some custom etched washers (1.3 mm diameter, 0.125 mm thick) that will represent the flanges on the boiler. There should be 13, including the front of the smokebox, but unfortunately one pinged off and defies being found, so the front will have to manage without.
However, there are two holes in the cab spectacle plate that locate the ends of the hand rail and these are much closer (approx 1.325 mm - I can just get a 1.1 mm drill bit between the hand rail wire and the boiler) to the boiler than the medium knob standout so I'm going to use Gibson shoulder-less knobs. The shank of these is 0.6 mm diameter, so the 0.65 mm holes I've already drilled are slightly oversize, but not enough to warrant plugging and re-drilling - just plenty of glue.
The drawback with these knobs is that they have no mounting flange (by design) but I've found some custom etched washers (1.3 mm diameter, 0.125 mm thick) that will represent the flanges on the boiler. There should be 13, including the front of the smokebox, but unfortunately one pinged off and defies being found, so the front will have to manage without.