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

[Edward H. Lybarger]

Could it depend in some degree how worn the rail is?  We have lots of street
specialwork at PTM where the wheel flanges clearly make the contact, but
none of it approaches new.

I had always been taught that riding on the flange was normal, too.

Ed

-----Original Message-----
From: pittsburgh-railways-bounce at lists.dementia.org
[mailto:pittsburgh-railways-bounce at lists.dementia.org]On Behalf Of Bob
Dietrich
Sent: Thursday, December 14, 2006 10:17 AM
To: pittsburgh-railways at dementia.org
Subject: [PRCo] Re: Fwd: Re: Double--Point__RR__Turnouts-__-1940--1950


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