Why do steep (90degish) crossing need guard rails ?


D

DALDEI

Member
I just completed my first attempt at a hand-made crossing. This was done totally from scratch as there were no jigs/assembly fixtures available and also just to see if I could do it. I think my results were "barely acceptable" ...

Here's an image of it almost complete
http://trains.calldei.com/?attachment_id=131

I've since added the inner guard rails and screwed up many things trying to gap the rails ... but it seems to have survived.

After completing I came to think "WHY" ... Why are guard rails necessary for this kind of crossing ? I can understand a very shallow angle crossing like a turnout (say 10deg , 20deg etc) but this is 75deg and even the 90deg crossing I printed out from handlaidtrack.com had guard rails.

What for ? I simply cannot imagine the wheels jumping track and taking a 90deg turn without them. Are guard rails really used on prototype tracks for this angle ? or is it a generalized pattern with no clear boundry of when they are not used ?

I ask becuase not only was it HARD !!! (16 seperate corners assembled) and I didnt get them all as snug as I wanted (but fear trying to move them without totally burning out the PCB's ) ... but as I run the trains trains through they seem to do no useful effect ...

Whats the point ? Could I just have made the crossing with NO guard rails and it worked just fine ?
 
Yep, guard rails are there. Anytime you're putting a gap in a track, you run the risk of a derailment, and guard rails are there to help keep the flanges and wheels on the track during that gap. Not that much of the wheel is in contact with the rail to begin with (just a few square inches).
 
But the strange thing is the guard rails are gapped at the same exact place the main/leading rails are gapped !
What good can that do ?
 
They have to be gapped for the crossing route's wheel flanges to work.

There is more flange available for the guardrail to hold in place than there is wheel tread that sits on the rail.
 
ICG/SOU said:
They have to be gapped for the crossing route's wheel flanges to work.

There is more flange available for the guardrail to hold in place than there is wheel tread that sits on the rail.
Click to expand...

Also as one wheel set passes the gap the other set is still in the guard rail area to keep the whole truck in place and not derailing.
 
DALDEI said:
But the strange thing is the guard rails are gapped at the same exact place the main/leading rails are gapped !
What good can that do ?
Click to expand...

There's a couple of reasons. First of all, the part of the flange that's below the head of the rail is longer than the gap in many cases, so some part of it will still be in contact with the guard rail. Having the rail on one side and the guard rail on the other side means you have a lot of guidance for the wheel.

Also, you should consider the truck as a whole. In most cases, trucks have two or more axles, pilot and trailing trucks on some steamers being the most common exception. When one wheel shifts one direction, the other wheel usually shifts the other direction. When it does so, hitting the guard rail will help keep things from shifting too far. The whole goal is to prevent the edge of the flange from hitting that tiny point at the end of the gap.

If it strikes the point directly, it may go a different direction than you intend. That's not good, obviously.
 
flh80 said:
Also as one wheel set passes the gap the other set is still in the guard rail area to keep the whole truck in place and not derailing.
Click to expand...


I still dont see this. For near 90deg crossings the gaps are nearly exactly opposite each other so when one wheel is across the gap (say on the left) the opposite wheel (on the right) is *also* on a gap.

It doesnt seem to hurt any but I cant visualize how its helping either.


OH OH OH I get it !
When you look at the full truck, instead of just a pair of wheels.
The rear part of the truck is still protected by the guard rails as the front of the truck goes over both gaps !!!!
Still amazing it works :)
 
Right, consider both (or in some cases all three) axles! The truck moves an entire assembly.
 
DALDEI said:
I still dont see this. For near 90deg crossings the gaps are nearly exactly opposite each other so when one wheel is across the gap (say on the left) the opposite wheel (on the right) is *also* on a gap.

It doesnt seem to hurt any but I cant visualize how its helping either.


OH OH OH I get it !
When you look at the full truck, instead of just a pair of wheels.
The rear part of the truck is still protected by the guard rails as the front of the truck goes over both gaps !!!!
Still amazing it works :)
Click to expand...

You got it!
 
In the case of switches., some have "self guarding frogs".
Have fun with that one! :D
 
also think about this. the crossing sees alot of traffic and the slaming of the wheels often jarrs the metal around the crossing. the gard rails are there for safty and to help guide a wheel that may be pushing to one side. If you look at a real Crossing you will see that the aera around the "Diamond" has alot of Iron around it to protect the rails around it.
 
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