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Movable point frog

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Movable point frog
Posted by ndbprr on Sunday, April 4, 2021 7:21 PM

Saw a picture on the net of a movable frog turnout that creates a solid rail in the frog and switchs when the points switch. Anybody know of a location in the USA?

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Posted by doctorwayne on Sunday, April 4, 2021 7:56 PM

I'm sure there are lots in the USA, but mine was on my layout here in Canada.

I'm pretty sure that Sheldon will have some on his layout, too. 

They're also often seen on real railroads, especially for high speed trains.

Wayne

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Posted by Outsailing86 on Sunday, April 4, 2021 8:35 PM

Amtrak northeast corridor, BNSF/UP powder river basin, UP around Chicago on Geneva Sub (Metra) are some examples

UP is biggest user 

 

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Posted by jeffhergert on Sunday, April 4, 2021 8:37 PM

They're common on the major railroads now.  Most of the dispatcher controlled switches on the UP across Iowa have moveable point frogs.  Some of the CNW installed switches with regular frogs still exist in some places.  Almost all UP new or replacement dispatcher controlled switches are equipped with them. 

Jeff 

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Posted by jjdamnit on Tuesday, April 6, 2021 11:50 AM

Hello All,

Can you post a link or photo?

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by Overmod on Tuesday, April 6, 2021 12:54 PM
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Posted by dehusman on Tuesday, April 6, 2021 10:30 PM

Also called a "swing nose frog".  The tall thing with a sign on it is a blower to blow air over the frog in the winter so it doesn't get jammed with snow and ice.  The duct work is for the blower.  The three part silver thing behind the ductwork on the ground is the switch motor to drive the frog point (just like a dual control motor on the switch points.)

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by Overmod on Wednesday, April 7, 2021 12:41 PM

To put this in a little context, see the difference in this picture (from an earlier thread) that shows this frog design in context.

https://www.railpictures.net/showimage.php?id=240339&key=8928380 

Note that this does not involve a stub-type 'perfect' full railhead contact patch through the frog area, as some higher-speed designs use.  But also note the difference between the heroic mechanism assuring correct geometry under load for the switchpoints proper vs. what is needed for the little movable point in the high-speed frog... 

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Posted by ndbprr on Friday, April 9, 2021 7:31 AM

Since the frog point needs to be able to move back and forth doesn't that expand the gap to the stationary rail in the direction it is thrown? Is that a potential problem from the constant impacts from the wheels?

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Posted by dehusman on Friday, April 9, 2021 8:20 AM

ndbprr
Since the frog point needs to be able to move back and forth doesn't that expand the gap to the stationary rail in the direction it is thrown? Is that a potential problem from the constant impacts from the wheels?

Don't understand which gaps you are talking about.  The whole idea of a moveable point frog is it eliminates the gap and provides a near continous surface to eliminate impacts.

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by Overmod on Friday, April 9, 2021 12:02 PM

ndbprr
Since the frog point needs to be able to move back and forth doesn't that expand the gap to the stationary rail in the direction it is thrown?

Doesn't matter because there's no way a wheel will touch the 'expanded' side gap.  When the swing nose is aligned with a 'stock rail' there is nearly perfect metal support for the gauge corner across to the rim edge of the contact patch on the wheel, all the way from the tip to the curved joint hinge or flexpoint at the 'heel'.

This also tells you why flange bearing in such a swingnose frog is not needed, as it is in a high-speed diamond crossing or some higher-number conventional frogs...

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Posted by ndbprr on Saturday, April 10, 2021 2:30 PM

I  assume the frog point has a pivot at the back end that contacts the rails after the frog and the switch machine pivots the front against either rail on the entry end. It should be impossible to move the front if the back ends are flush with the rails in both positions. So if the point is moved in one direction the back end in that position is rotated away from the exit end to some degree.  This may be an extremely small gap or as much as 1/4". When the wheels get to the back end of the frog I am wondering about wear to the ends of the frog and rail.

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Posted by gmpullman on Saturday, April 10, 2021 2:46 PM

ndbprr
I  assume the frog point has a pivot at the back end

There's enough flex in the length of the rail that makes up the frog that no pivot is necessary.

 Movable frog point by Steve Cox, on Flickr

Note the rails that make up the "moving point" are very similar to a pair of switch point rails side-by-side in that they nest due to their being carefully machined so that the base and head practically form one piece of rail but there is a "sliding action" between the two.

Three switch motors are required to operate this movable point frog turnout:

 Switch with movable frog point by Steve Cox, on Flickr

Note, too, that each motor is driving two tie bars through linkage (four tie bars total on these long points.

Good Luck, Ed

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Posted by OldEngineman on Saturday, April 10, 2021 9:30 PM

Ed wrote: "Three switch motors are required to operate this movable point frog turnout"

On Amtrak, and perhaps on Metro-North as well, the 80mph crossovers have FIVE motors per switch. Three on the points, two more on the movable frog.

That means TEN switch motors for a single crossover. If something doesn't work, the maintainer has to check all of 'em...!

And if for some reason you're on the engine and have to get talked by a signal to go over these, you've got to be watching out for misalignment on the frogs as well as the points...

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Posted by dehusman on Saturday, April 10, 2021 10:15 PM

ndbprr
I  assume the frog point has a pivot at the back end that contacts the rails after the frog and the switch machine pivots the front against either rail on the entry end.

There is no pivot on the frog, just like there is no "pivot" on the points.  The rail bends.

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by Overmod on Saturday, April 10, 2021 10:19 PM

Note that in the picture I linked, there are EIGHT motors on the points and three on the frog.

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Posted by zugmann on Sunday, April 11, 2021 3:37 PM

There's also spring-loaded frogs.  Frogs move as well, but no motors, and they return to normal after you go through them. 

 The opinions expressed here represent my own and not those of my employer or any other railroad, company, or person.

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Posted by gmpullman on Sunday, April 11, 2021 10:06 PM

zugmann
There's also spring-loaded frogs.


 

 Frog_Sprung_drawing (2016_08_17 08_08_12 UTC) by Edmund, on Flickr

Regards, Ed

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