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Showing posts from April, 2007

Coupling Rods

The spacing of the coupling rod centres is critical to the free running of the loco. I measure each side separately and comparing it with the drawing. Any inaccuracies in making up the axle-boxes or in setting the crank-pins will show up here. I started by marking out the centres and outline on the rod blank, then drilled the centres, starting with a small centre drill, then drilling out at (say) 2BA clearance at one end, and 2BA tapping at the other. The rods tapered from 3/8 to 1/4 in. - i.e a taper of 1/16 in. on each side. So I marked out the centre line on the support bar, and another, offset by 1/16 in. I drilled and tapped a fixing for one end of the bar on the centre line, and attached the rod blank. Then I lined up the other centre on the 1/16 in offset line, clamped and drilled through 2BA tapping. Now I removed the rod blank, and opened the 2BA tapping hole on the rod blank to 2BA clearance. Also I tapped 2BA threads in the support bar and bolted the two together. I clampe