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topic: 3165Slips and Half-Scissors
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posted: 30 Dec 2017 15:25

from:

RogerW
 
Northampton - United Kingdom

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Slips and Half-Scissors

What are the general rules for determining what to use regarding a double slip vs two points heel to heel?

Similarly what would determine whether to use an inside single slip vs outside single slip vs half scissors configuration.

Many thanks - RogerW

posted: 30 Dec 2017 20:10

from:

Rob Manchester
 
Manchester - United Kingdom

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RogerW wrote:
Slips and Half-Scissors

What are the general rules for determining what to use regarding a double slip vs two points heel to heel?

Similarly what would determine whether to use an inside single slip vs outside single slip vs half scissors configuration.

Many thanks - RogerW
Hi Roger,

Inside or outside ( or even semi outside ) slips ar usually determined by the crossing angle of the tracks. The radius of the rails on the slip tracks needs to be within sensible ( lower ) limits. Try using the make slip function on tracks crossing at different angles and check out the positioning and radius of the slip tracks. Check rail space also needs to be considered depending on what gauge/scale setting is in use. It may depend if the slip was being added to an existing track layout as to what will give a suitable fit with operational flexibilty.

The prototype is the best guide as to what would have been used if you can find a suitable reference.

Rob


posted: 31 Dec 2017 13:16

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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RogerW wrote:
What are the general rules for determining what to use regarding a double slip vs two points heel to heel?
Hi Roger,

Two turnouts would require a lot more space than a double slip. Slips are often arranged in a ladder formation diagonally across several running lines. To replace them all with double turnouts would use vastly more space, and also mean traffic on the ladder road would be subject to repeated reverse curves.

p.s. such turnouts are toe-to-toe, not heel-to-heel.

Similarly what would determine whether to use an inside single slip vs outside single slip vs half scissors configuration.
This is usually down to radius and crossing angle. Inside slips are generally not shorter than 1:6, the slip road is very sharply curved at that angle and subject to a severe speed restriction. You wouldn't find a 1:6 slip road as part of a running line.

Outside slips allow a much easier radius and can be used at shorter crossing angles, but require a lot more space. Here's a nice outside slip. You can see how much longer it is than the diamond-crossing. It would be an impossibly severe curve as an inside slip entirely within the diamond:

outside_slip_shrewsbury_1978_600.jpgoutside_slip_shrewsbury_1978_600.jpg

The choice between an outside slip and a half-scissors is simply one of track alignments as to which best fits the site. Half-scissors are even longer than an outside slip. If the slip above was replaced with a half-scissors, the platform would need to be narrowed, the platform capacity would be reduced a bit, and the far turnout might conflict with the square crossing just visible in the distance.

Note that there is an important difference between a double outside slip (not very common) and a full scissors crossover. In the latter both side roads can be used at the same time. That's not possible in any sort of slip.

regards,

Martin.



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