Sunday, 6 September 2009

Switch blades

I had quite a productive modelling session yesterday afternoon - at least by my current standards -getting the remaining four switch blades filed up and ready for installation.

Filing switch blades isn't a particularly difficult or even time consuming task, but does require a bit of care. By the time I got to the fourth blade it took me about 10 minutes to make. The process is nothing revolutionary, but for those who are unfamiliar with it, here's what's involved:

First the rail is cut to length, allowing for a small (0.5mm - 1mm) insulation gap at the heel and for the toe to be flush with the leading edge of the first slide-chaired timber. Depending on the curvature of the turnout, one switch blade will be marginally longer than the other, so it's important to remember which blade you are working on.

After cleaning up the rail ends with a file, the rail is clamped to the right hand edge of an offcut of veneered chipboard, leaving a couple of inches of rail free to work on and with the end of the rail flush to the front end of the board. Using a small flat needle file, a taper about 25mm in length is filed into the head of the rail only (taking great care to avoid the base of the rail). The taper should just cut into the web of the rail at the extreme end.

Then, using a small pair of pliers, a very slight bend is made in the rail at the end of the taper, so that the tapered edge lines up with the straight edge of the rail - a bit of eyeballing down the length of the rail is called for.

The rail is then turned over and clamped down again but with the protruding flare of the rail base slotted into the groove so it lies flat. A full-width taper is then filed into this side of the rail, the length determined by the angle of the turnout (for a standard 'C' turnout this equates to around 33mm - at least for the GWR type I model). The rail should taper to a fine point a the end, with just the base on one side protruding.

Finally, the end of the blade is rounded off slightly at the top, and cleaned up ready for installation.

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