Monday, 8 July 2013

A pair of points

I'm finally nearing completion of the track-laying, so here is the story of the most tricky part - the points of course! I'm very glad I only have two to build for this layout, I'm sure I'd get better with practice but point building is very tedious to me, especially using the spiked construction of the KB Scale track representing the sectional industrial track.

The rails were cut and shaped onto plans of the points. Without soldered construction and with so few sleepers the crossing vee (frog) area of the point would be very weak. I decided to assemble this onto a small, thin sheet of brass, justified as these type of industrial points often had steel plate under the crossing. Track spikes help with the assembly here.

The point blades have wire droppers soldered to both the hinge end and the tie-bar end, these will form the pivot and the attachment to the tie bar. The "proper" construction with tiny brass tabs under the blades riveted to tie bars is well beyond me, so I have a cheat method. Once ready, and not forgetting to add feed wire droppers, the rails were then transferred to the plastic sleepers on the layout.

The rails were carefully spiked in place checking the gauge. Slots had been cut under the tie bar for the wire droppers, and holes through the sleeper and foam-board at the hinge point, so the blades could be dropped in place. The tie-bars are made from 40" plastic (they will be cut down) through which the droppers pass, although these are largely cosmetic they do help keep the blade spacing. At present I have yet to fit the check rails.

The real action is underneath. The real tie bar is a strip of PCB (sliding on a piece of black plastic), through which the droppers pass, then small pieces of PCB are soldered to each dropper to act as "nuts". The droppers are therefore free to rotate relative to the tie bar as it moves sideways. The same method of PCB soldered to the wire is used to hold the pivot wire in place too. Note that the blades are electrically isolated from each other and a wire feed will be attached to the bottom of the hinge wire.

The points are operated by wire-in-tube, a steel wire through the tie-bar passes through a plastic (PTFE?) tube which is held in place by lots of hot-glue and pieces of foam board so it cannot move sideways. A Z-bend in the wire by the tie bar acts as a spring for any slack. The other end is attached to a slide-switch, which not only will switch the electrics for the point vee, but also acts as the latch to hold the point over. Actuation is by dowels to the side of the layout, attached to the slide switches with a screw, more on this when I get to the wiring.

This isn't precision engineering but so far the points seem to work, which is the point ... if you excuse the pun. That said, they've not been tested by a loco yet! Time to finish the last bits of track and connect up the wires.
Posted by Picasa


JeffB said...

Looks great Michael! I'm always impressed with what you are able to accomplish with a minimum of tools... That is true skill and talent!

Christian said...

Looking really good! I totally agree with the bit of plate under the crossing vee - as you say it's very prototypical and has saved me from madness a few times. Liquid solder is also handy to flow around the vee.