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...a technical digression

kitpw

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The system devised to motorise the 11 points on Swan Hill may be of interest to others. I wanted a simpl(ish) mechanism using servos controlled from a Megapoints board and toggle switches – all new to me – to drive a protypical angle crank (rather than a slot in the baseboard type arrangement).

 

The photos show servos mounted under the baseboard in a piece of aluminium angle slotted to carry the servo. The servo drives a short length of 2mm steel rod fitted with spade connectors each end. This drive rod turns a vertical 3mm steel shaft mounted in a 4mm steel bolt bored 3mm lengthwise. The 3mm shaft is turned down at the top end to make a 1.5mm diam x 1mm long stub to which a point crank is hard soldered. The whole assembly is mounted on a small piece of plywood and the 4mm bolt holds it against the underside of the baseboard, assisted by one or two screws as necessary. On top, the bolt head is lost in the track underlay. The whole lot can be assembled and tested on the bench before fitting.

 

Above board, I end up with a fairly p/t (prototypical) arrangement with an angle crank located adjacent to each set of point blades. The cranks are the correct p/t length from pivot to pin connection but a bit beefier than scaled p/t cranks. The crank sits on the small rectangular base plate (p/t cast steel), itself sitting on a larger plate (p/t sheet steel) which often carries more than one crank/compensator or whatever.

 

The point blades are joined using a version of the excellent system devised by David Nicolson and described in his article 'Floating Scale Pointwork' in MRJ 227 but amended dimensionally to make use of 2mm diam red plastic straws as supplied with WD40 (actually ex Ebay by the handful) for the insulating joiner. The rail section is drilled using jigs to control dimensions, all as described by David Nicolson, and the sleepers are set out to suit those dimensions. The remainder of the point rodding is cosmetic and I have yet to devise a sliding connection of cosmetic rods to working cranks... more on that when I've cobbled something together.

 

The loose fittings in the last photo are parts for the only facing point lock on the layout - work in progress.

 

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Andy - all the angle cranks are hand cut, filed and drilled out of 0.95mm brass sheet. A bit of a labour but they need to be robust enough to do the job without buckling: they are also silver soldered to the 3mm steel drive rod and have to be able to stand that amount of heat.

Kit PW

 

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