So PECO doesn't make Electrfrogs C55 anymore?

[Point353]

Did your ballast clog up with wheel droppings? 

The Mössmer foam ballast I was then using clogged itself up as it gradually disintegrated.
http://davidksmith.com/birth-of-n/mossmer.htm

[peteski]

The Arnold Rapido trains with which I started out always ran well on their track with its unprototypically shaped rail profile.



(http://davidksmith.com/birth-of-n/arnold.htm)

That image perfectly demonstrates what I mentioned earlier, that regardless of how wide the rail head is, there is only a very small contact area with the wheel.

[ednadolski]

As rail gets smaller and smaller, if we were to properly make it proportionally thinner, we end up with a LOT less physical contact surface with the wheels for electrical pickup.

I'm not sure that is quite accurate, since as noted above, the wheel tread is supposed to have about a 20:1 taper (at least on the prototype... in N scale it's hard to imagine that anyone could machine something that accurately). Rail head likewise is supposed to have a sort of rounded/convex profile.

The ME C55 rail (not sure about Atlas, Peco, ...) actually is a pretty close representation of prototype 75 lb. rail in HO scale, wrt height and railhead width.  But that same railhead width in N equates to nearly 5 scale inches.


Ed

[ednadolski]

You could probably make the railhead as narrow as a single edge razor blade ...

That would be some pretty dangerous rail... lots of nicked fingers.... 

Ed

[mmagliaro]

I know the wheel treads are tapered, but I don't buy that the taper is significant enough to cause the wheel to actually only contact on such a small area.  I think that drawing of the Rapido track vs a more square rail profile exaggerates the wheel taper and rail edge contact. 

Having said that, you bring up an interesting point about rolling on a knife edge.  If the wheels were riding on the whole top surface of the railhead, and we then made the railhead much thinner, then the surface area of contact would be less, but the actual pressure on the contact area would be *higher*  (same weight supported by less surface).  So thinner rail might actually work better!

[robert3985]

I'm not sure that is quite accurate, since as noted above, the wheel tread is supposed to have about a 20:1 taper (at least on the prototype... in N scale it's hard to imagine that anyone could machine something that accurately). Rail head likewise is supposed to have a sort of rounded/convex profile.

The ME C55 rail (not sure about Atlas, Peco, ...) actually is a pretty close representation of prototype 75 lb. rail in HO scale, wrt height and railhead width.  But that same railhead width in N equates to nearly 5 scale inches.


Ed

It's a 3 deg. "slope" for an NMRA RP-25 wheel profile, which is easy to machine and mass produce, as is the radius of the fillet (.010" radius) and the converging radii of the front and rear surfaces of the flange (.012" radius for both).

Photo (1) NMRA RP-25 Wheel Standard:


Photo (2) Prototype Wheel Profile:


It appears that the NMRA RP-25 Standard's 3 deg "slope" for the wheel's tread taper is less than the prototype's 1:20 taper spec., but the radii of the flange fillet and the rest of the flange profile for the prototype is much more complicated than the RP-25 standards

Interestingly, after looking through the entire NMRA standards list, there is no standard for rail profiles...zero mention of any rail profile whatsoever.Edit: Thanks @Point353 for the correction about NMRA standards concerning rail profiles.  I looked through the standards several times and never saw it.  Here's the link: https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-15.1.pdf

If you take the time to follow the link to the NMRA's rail profile standards (or "Recommended Practices"), you will see that the tops of the railheads are flat, parallel to the bottom of the rail foot.  In contrast to model rail, prototype rail has a curved surface for the top of the railhead as can be seen in the following diagram...

Photo (3) - A.R.E.A. 136 lb rail cross section with foot width, height and railhead width for N-scale in red numbers:

I know the wheel treads are tapered, but I don't buy that the taper is significant enough to cause the wheel to actually only contact on such a small area.  I think that drawing of the Rapido track vs a more square rail profile exaggerates the wheel taper and rail edge contact. 

Having said that, you bring up an interesting point about rolling on a knife edge.  If the wheels were riding on the whole top surface of the railhead, and we then made the railhead much thinner, then the surface area of contact would be less, but the actual pressure on the contact area would be *higher*  (same weight supported by less surface).  So thinner rail might actually work better!

I attempted to find a diagram of how a model train's wheel rolls on model rail but failed.  The prototype railhead/wheel tread relationship is much different since prototype rail is usually spiked to "inclined" tieplates, which tilts the rail significantly towards the center of the track gauge, which increases the contact patch between prototype wheels and railhead.  I'll post a photo of a prototype wheel profile poised above a tilted or inclined railhead to illustrate that even on prototype wheels and rails, the contact point is small in overall comparison to the total width of the wheels tire tread.

Photo (4) - Prototype wheel tire tread and inclined railhead relationship:


The contact area indicated on the prototype wheel is not what is actually riding on the rail, but what area the contact patch (which is quite small) slides around in during normal operation.

Note that with model railhead not being inclined or curved, the primary contact region "Wheel tread rail ball" is going to decrease, decreasing the area of the model wheel tire's contact patch also and moving it more to the inside of the railhead.

So, I am going to agree that rail head width in model railroading has little to do with the electrical contact patch area, but would be located close to the inside edge of the railhead, and that the taper on model railroad wheels that comply with the NMRA RP-25 standard is significant.

Cheerio!
Bob Gilmore

[peteski]

I know the wheel treads are tapered, but I don't buy that the taper is significant enough to cause the wheel to actually only contact on such a small area.  I think that drawing of the Rapido track vs a more square rail profile exaggerates the wheel taper and rail edge contact. 

Having said that, you bring up an interesting point about rolling on a knife edge.  If the wheels were riding on the whole top surface of the railhead, and we then made the railhead much thinner, then the surface area of contact would be less, but the actual pressure on the contact area would be *higher*  (same weight supported by less surface).  So thinner rail might actually work better!

I have to disagree Max.  Think about it.  Metal surfaces are hard (not like soft rubber which will squish and create larger size contact area). As I see it, unless the rail head surface and wheel surface are perfectly flat and parallel to each other, the contact area of those non-parallel surfaces will be extremely small.

[Point353]

Interestingly, after looking through the entire NMRA standards list, there is no standard for rail profiles...zero mention of any rail profile whatsoever.
Bob Gilmore

Have you checked RP15.1?
https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-15.1.pdf

[ednadolski]

Have you checked RP15.1?
https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-15.1.pdf

Wow, Code 32 rail... who makes that?

Ed

[ednadolski]

So thinner rail might actually work better!

Not from a longevity standpoint tho

Ed

[ednadolski]

@robert3985  I can't see your pics... just the gray circle with a dash thru it

Ed

[dem34]

Wow, Code 32 rail... who makes that?

Ed

Pretty sure DKS had a thing when he was still in Z scale where he used Code 25 Flat wire for rail from a company that I think made jewelry wire, dont think you can get stuff at that size commercially.

[robert3985]

Have you checked RP15.1?
https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-15.1.pdf

I completely missed that, even after going through all of the standards several times.  THANKS!!

I've made an appropriate correction in my post.

Cheerio!
Bob Gilmore

[wcfn100]

I completely missed that, even after going through all of the standards several times.  THANKS!!

Maybe because it's not a standard.

Jason

[robert3985]

@robert3985  I can't see your pics... just the gray circle with a dash thru it

Ed

Ed, I re-uploaded my pic locations.  Did that do the trick??

Cheerio!
Bob Gilmore