Do point rails bend or pivot?

Model Railroader General Discussion (Model Railroader)
1

I’ve been out and about looking at prototype turnouts and noticed that the older turnouts, esp. the ones that are sharp, have the closure rails in a different section than the point rails. The points appear to be about 1/3 the length of the closure rail. Don’t know if that radio is a hard and fast rule.

On modern, esp. high-speed turnouts, however, the closure and point rail is a single segment and instead of pivoting, the rails seem to bend when the switch is thrown.

3 questions:

  1. What is the ratio supposed to be of the closure and point rails?

  2. Are prototype point rails actually bent when the switch is thrown?

  3. How accurately do our model turnouts reflect the prototype w/regard to the dimensions and movements of the 1:1?

(as you can guess, I’m building turnouts and this info will be helpful)

2

On my layout, both! [banghead]

Seriously, I feel certain that they all pivoted and slid on greased timber. It would fatigue the metal otherwise, and reguire mountain apes to bend the rails.

3

Prototype switch points all bend unless the tracks run in the street (light rail or trolleys). Railhead configuration is equivalent to a modified I- beam, which makes it very stiff. The points are essentially filed into a thin flat plate which makes them very flexible (ever push on the hood of your car). This thin crossection requires relatively little force to move. The low stress level an infrequent motion eliminates the possibility of fatigue. Model turnouts have to pivot because the alloys (nickel-silver, brass, or steel) is not as proportionately as soft or flexible and prototype rails. This is why modelers who handlay their track can get away with spiking every fourth tie instead of every one that the prototype has to use.

The street tracks use a pivoting point because the flangeway used to protect the pavement makes this rail very stiff and unbendable…

4

thanks, Leon for clearing this up.

5

Yes, thanks. I learned something.

6

Thanks, I’ve been wondering about that one for a while too!

7

In the last 45 years, I have seen numerous articles on hand laying track where the the points bend instead of having pivots.

8

Actually, in “classic era” turnouts, the points are attached to the closure rails with standard joint bars, which allows for a modest amount of pivoting at the heel of the point – it only takes a couple inches movement over a point length of typically about 16 feet. The newest turnouts I’ve seen, however – on the LA-area commuter rail system at San Bernadino, Calif., were actually made just the way I build model turnouts, with a continuous length of rail forming the point and closure rail. The ends of the closure rails are ground down to form the points, and the rail bends as the points move.

There isn’t a ratio between points and closure rails. More typically, a railroad uses a standard-length point for all or most turnouts, and varies the length of the closure rail as the lead – distance from sharp end of point to point of frog – increases with the frog number.

Model turnouts built to NMRA standards vary quite a bit from prototype turnouts, primarily in the width of the flangeways and the clearance between open points and stock rails. The wider model flangeways affect the proportions of most turnout parts. Compare typical HO turnouts made to NMRA standards with those built to Proto 87 standards and many of the differences will be obvious.

You can make one significant improvement without adopting finer track and wheel standards, however. If you use isolated frogs and hard-wire the closure rails to the adjacent stock rails – as is typically done for so-called (but mis-named) “DCC-friendly” turnouts – you can reduce the point clearance to equal the flangeway clearance. This will make any commercial or handbuilt turnout look more realistic.

so long,

Andy

9

OK, I feel better about my post earlier on; don’t come aboard me too hard, guys, but I actually have not walked amongst rails and switches in about 40 years…yeah, I know, I know.

So, my experience was in a steam system in the Andes back in the late 50’s and early 60’s. I was sure that I recall the points pivoting. Whew, I thought the KRAFT disease was starting early! [:D]

Thanks, again, Andy, for setting us straight.

10

Andy writes: “The newest turnouts I’ve seen, however – on the LA-area commuter rail system at San Bernadino, Calif., were actually made just the way I build model turnouts, with a continuous length of rail forming the point and closure rail.”

Andy,

So your closure and point rails are one rail like most prototype that I’ve seen. Are you bending or pivoting the rail? If bending, how far towards the point to you spike it? That’s an awefully long rail to pivot if you’re using that method, without support (other than the spikes at the end towards the frog. (hope my question is clear).

11

Prototype switches are (for the most part) “kits” the railroads buy from manufacturers. the points are separate pieces that come in standard lengths. Each point length is used with several frog numbers. There is an upper limit to how long a switch point can be since if it gets too long its essentially an “unspiked” piece of rail and the weight of the train will cause the rail to move out, widening the gauge and derailing the train.

Dave H.

12

So then you would have your ‘good points’ and your ‘bad points’ right Dave?

Sorry, but this evil little character on my shoulder made me do it! lol

13

David,

I would suggest that you buy a Bk Enterprises or Railway engineering finished turnout that you have to spike down to ties that you lay. They are a great way to get your feet wet on the way to handlaying and many of the questions that you have will be answered by your experience with this type of turnout. I have just laid three of them in my yard and while they take some time, man they come out great.

There was an article in MR recently on making micro engineering turnouts DCC friendly that I have found to be of help also. Particularly on replacing the throwbars with PC board bars. This allows for the better spacing Andy was refering to earlier and I was able to improve the fit of the points. I have taken to soldering the pivot point to the closure rails on my turnouts that have pivots to increase electrical reliability. Haven’t had any problem with them being too stiff. Not sure of the article date (maybe some one will jump in here). Question for Andy, Are you isolating the frog on your switches??? I can’t bring myself to cut that beautiful arc made by the closure rail running out to the points. Just curious how you are handling this.