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Tuesday 28 January 2020

Project 20 - 0 Gauge Layout - Part 4

This is the third time I have scratch built turnouts. Previously I made turnouts for 00 and EM gauge layouts. Now it is the turn of 0 gauge. I am making my own to save expense. The cost works out to be about £10 (using some heavily discounted products off eBay) whereas proprietary r-t-r turnouts are about £50.

The parts that were troublesome for me to make in the past were the switch blades, to achieve good electrical contact with the stock rails and effective switch blade movement. The former was a problem because I do not use a direct frog electrical feed, which would require the complexity of an electrical switch to supply the correct polarity (usually automatically operated by a point motor). I need the switch blade to provide a reliable frog feed with the correct polarity when it touches the live stock rail.

I had already decided operation would be manual for this small layout and I wanted control to be my means of a lever alongside the turnout similar to the prototype.

I proceeded with trepidation, not really having solutions at the outset for the above. But, along the way I came up with reliable designs for those parts.

The fundamental parts for the turnout are:
  • 3mm plywood sleepers stained a dark oak.
  • Peco chairs and slide chairs.
  • Peco code 124 rail
  • Fabricated brass plate foundation for the frog and closure rail assembly.
The sleepers were lightly glued at the ends to a Peco paper template. The template peeled away after completion.

The rails were cut and formed using the template as a guide and the chairs slid over. Each chair was glued to the sleepers. Now, I found MEK liquid did not work and superglue was dodgy (Peco advises pins). I used 'tacky white glue' that claims to stick virtually anything. It did work but needs a long drying time. Some chairs that are under stress came adrift and were reinforced with superglue.

The only gauges I used to set the rails was a vernier calliper set to 32 mm and a 1.75 mm drill shank to set the check rails.

And so to the switch blades.

I made the switch blade and closure rail to be one piece (usually they are separate and hinged with a rail joiner) and soldered it to a brass foundation plate together with the frog. Thus, the whole lot is electrically joined. To aid movement I cut nicks in the bottom flange of the rail at the hinge point.

To set the gap between the two blades I used stretcher bars, like the prototype. The bars need to be stiff. I used pieces of EM gauge rail I had in stock. The style of the bars is not exactly as the prototype but they are in the correct place and look the part.

Needless to say electrical contact between switch blade and stock rail was unreliable. I spent a long time thinking of a solution and nearly reverted to a separate electrical switch until I had a eureka moment.

Taking some springy phosphor bronze strip I set it in the baseboard and in line with the open switch blade such that the blade pushes into it slightly for a good contact when 'on' (top blade in photo above). Each contact is wired to the opposite live stock rail beneath the baseboard. The position of the contact must be checked to avoid touching the wheel of a passing loco when in the 'off' position (bottom contact in photo above).

The manual lever control of the switch blades is quite novel, I think. I believe the prototype uses a sprung mechanism such that the lever is pulled and released in only one direction for each movement of the blades. I could not see a way of doing that so my lever is pulled one way and then the other to switch directions.

Looking at how the Peco 00 gauge mechanism works I adopted the same sprung method but, offset it from the turnout.

I 3D printed a sliding tie bar and housing for a Peco 00 gauge spring taken from a broken turnout. The tie bar has a 1mm wire through the middle that locates in a loop fixed to the nearest switch blade. The other end is upturned to fit into an angle crank.

A platform with a slot holds the lever that pivots in an integral bracket. The bottom of the lever locates in the same angle crank beneath the platform.

The platform and crank fit over the tie bar rod and is fixed to the sleepers either side.
The 00 gauge spring gives sufficient movement to hold the switch blade against the stock rail.

To Part 5.

To Part 1.

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