5" and 7 1/4" dual points

 
  goodlife Beginner

Help required please.  I have a large trackwork in 2 loops, one 5" and one 7 1/4" .  I am now wishing to make the 5" into a dual gauge with the 7 1/4".  Trackwork is no problem but I need assistance with point work.  A clear photo or drawing of a dual gauge point would be very much appreciated.
Regards
Barry

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  TomBTR Chief Train Controller

Location: near Sydney
Hi Barry, and welcome to the forum.

Sometime you should tell us about your track.

I can't help with photos at the moment although someone at our club posted several from South Australia on the wall last year. If you have not had an answer by then I could copy one or two next time I am there.

Just a hint:

The wheel profile of full size standard, broad and 3'6" gauge trains is near-enough the same. This simplifies multi-gauge special work.

Unfortunately the wheel profiles for 5" and 7 1/4" gauge trains are different. So, in theory, it should be impossible to set a check rail gap that is correct for both. Hence the complex moving-frog non-trailable points at Fairfield NSW and maybe other old club tracks. This remains true for fine scale 5" trains.

Fortunately 5" gauge trains built to the current AALS wheel profiles have a wheel tread that is wider than scale (although not the same as the 7 1/4" profile). If your 5" gauge trains are recent (I guess younger than 50 years but others might know better) then then the wheels are likely to be wide enough to allow you to widen the gauge of the 5" track through the points from 127mm to 129mm while leaving the 7 1/4" at 185mm. Then you can set the shared check rail gap at 9mm and it will pass both wheels without the opposite wheel going the wrong way.

I hope that this of some use.

Tom
  Allison1947 Station Master

Location: Campaspe Valley Railroad
Barry ignoring radius there are four basic kinds of points.

Standing at the sharp end of the points and looking up towards the two diverging legs you can decide which combination you need.

First is the curved or diverging route heading to the left or right?

Second is the common rail on the left or right?

When you have this you can as an example define the points as "A left hand" route and a "right hand common rail".

There will be 2 "Frogs" where the rails cross over. Their position s determined by the "handed" info e.g. LHRC (left hand and right common).

I do have some info on the ones at CVMR Echuca.
Allie
  Ned Ludd Assistant Commissioner

Location: Touched by the noodly appendage
G'day Barry,

Here's a pretty good photo I found: http://www.minitrains.com.au/images/products/T0M0-g3.jpg

The resolution is good enough to zoom in and look at the two dual gauge turnouts in the background. I must say the dual gauge single slip is rather nice, but definitely not for beginners!

Don't get too worked up over what seem to be conflicting wheel standards. The spacing of the wing rail (beside the V in the  crossing) is not important, as that rail is not touched by the wheel flange. It is actually just there to reinforce the end of the closure rail. The important dimension is the checking gauge, which is from the back of the check rail to the toe of the crossing.

When the wheelset meets the check rail, the check rail engages with the back of the flange, and ensures the flange of the wheel on the other side cannot strike the toe of the crossing. So if the flangeway of the crossing is built at 9mm for 7 1/4 gauge, it has no effect on the 5" gauge wheelset - the stock rail prevents the wheel going the other way. The worst you might get is a click if the outside edge of the wheel drops off the closure rail before the tread meets the toe of the crossing. I actually doubt that would happen.

Widening gauge is a good fudge if the check rail is on the common rail, but bear in mind that on real railways they often swap the common rail from one side to the other in order to simplify the geometry of the dual gauge turnout.

There is a lot of geometry involved in building turnouts, but you can get away with a hell of a lot too, as long as your back to back and checking dimensions are correct!

Where are you? I haven't done a dual gauge turnout, and wouldn't mind having a go...

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