[PRCo] Re: Fwd: Re: Double--Point__RR__Turnouts-__-1940--1950

[Bob Dietrich]

Fred and Jim, your explanations are very good, but hey raise a question in
my mind.  You both say that the right wheel must ride on the flange in the
flangeway.  I was under the impression that the tread spanned the gap
between the rail and the point, much like a standard railroad frog.  If the
flange rode on the casting it would quickly wear a grove in the casting and
cause some nasty bumping and deterioration.  

Am I misinformed on this?  Is the flange-way plus the width of the point in
the right-wheel casting really wider than the wheel tread?  I know models
span that gap but model wheels tend to be wider than prototype - but then so
do clearances.

Bob 

-----Original Message-----
From: pittsburgh-railways-bounce at lists.dementia.org
[mailto:pittsburgh-railways-bounce at lists.dementia.org] On Behalf Of Fred
Schneider
Sent: Wednesday, December 13, 2006 8:42 PM
To: pittsburgh-railways at dementia.org; McGuire Mark
Subject: [PRCo] Fwd: Re: Double--Point__RR__Turnouts-__-1940--1950

Mark and any one else who wants the long explanation:
I'm not sure if you got the gist of the single point switch versus  
double point switch from the model builder's diagrams but these two  
pictures are great explanations.

The first two URLs show double point switches ... both points move  
back and forth like a railroad switch.   Go out and look at any CSX  
or FEC switch in Jacksonville and you will understand the concept.    
Wheels rolling over it are always solidly guided on a steel point and  
the outside rail no matter which way it is set, left or right. (or  
left, right or center in the case of a three-way switch.)     The key  
to understanding here is that with a double point switch, the tread  
side of the both left and right wheels (and tread side of their  
flanges) always rides on the point or a fixed rail.  You will also  
notice, on the outside rail adjacent to the frog in each switch,  
guard rails, that prevent the wheel from following the wrong rail at  
the frog and derailing.

Now look at the Drake picture -- the third URL -  there is only one  
moveable point and that is built into the casting on the left rail.    
The point can move left or right.   At the present time in is moved  
to right and it will lead the car around the curve to the left.   The  
backside of the wheel will be forced by the tongue to roll to the  
left.   If the switch point is moved to the left, then it will force  
the front side of the flange to ride on to the point and the car will  
go to the right.   Note that the entire wheel may or may not ride on  
the point depending on which way it is thrown.       The small box  
near the hinge just contains a spring (in case) so that once thrown  
in will stay in that position.   The common position for the Drake  
switch was the other way from the way shown was the loop was finished  
and in service.

Now look at the casting to the right in the Drake loop picture ...  
the casting opposite to the frog ...  it has no moveable point .   It  
doesn't need one because the single point on the other side will  
force a car to go either way.   All it needs to do is support the  
weight of the car.   And because there cannot be a running rail where  
the car diverges, the car rides on wheel flanges.

Now where are the guard rails opposite the crossing frog in the Drake  
loop?   Ah, you don't need them because girder rail is used and the  
entire rail has a built-in flange along the inside.

If you study railroad switches, you will also see some self-guarded  
frogs with lips build onto the edge of the frog castings for use in  
industrial sidings but I know of no instances where they were used in  
high speed turnouts.

The single-point switches were quite adaptable to low speed city  
street operation.   They worked well at 5 to 10 mph.   But a high  
speeds cars tend to derail.   And that is which I noted that the  
European systems often use double-point switches in city streets and  
they tend to run like hell.   And they do it with safety.

If the explanation isn't clear, please come back at me.

Fred Schneider
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> http://lists.dementia.org/files/pittsburgh-railways/RR%20Double% 
> 20Point%20Turnout%20096.jpg
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> http://lists.dementia.org/files/pittsburgh-railways/03-Tylerdale% 
> 200096%20195xxxxx%20RSchramm.jpg
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> http://lists.dementia.org/files/pittsburgh-railways/03-Track%20Drake 
> %20Loop%20Construct%201953xxxx%2001.jpg 
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