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#4 vs #5 turnout

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#4 vs #5 turnout
Posted by Barry B on Wednesday, May 10, 2017 8:00 AM

What is the difference between a #4 turnout and a #5 turnout?

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Posted by Steven Otte on Wednesday, May 10, 2017 9:11 AM

One. [rimshot]

But seriously, folks... Turnout number refers to the amount of spread of the rails coming off the frog. The number is the ratio of the distance from the frog to the distance the rails spread apart. On a #4 turnout, the rails are 1 unit (inch, cm, scale foot, whatever) apart 4 units (inch, cm, scale foot, etc.) from the frog. On a #5, they're 1 unit apart 5 units from the frog. So smaller numbers are sharper. Typical numbers that commercially offered turnouts come in are #4, #5, #6 and #8. These are much sharper than on the prototype, where #12 is considered very sharp and #20 is more typical.

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Posted by peahrens on Wednesday, May 10, 2017 9:17 AM

The number refers to the frog angle.  The #4 frog (and it's extension except on a curved turnout) diverges 1' every 4' (or 1" every 4") and is a more severe angle.  The #5 diverges 1' every 5'. 

There are other differences in the other parts of the turnout.  A key one is the curvature of the point rails and closure rails (between the point rails and frog).  On the #4 they will be sharper.

You can find extensive detail in the NMRA turnout dimensions Recommended Practices area and other related pages:

http://www.nmra.org/rp-122-turnout-dimensions

In practical terms, a #4 is pretty sharp.  Some locos and long rolling stock (like 80' cars) may not take it.  A #5 is much more forgiving.  I used #5s in my yards, #6 for mainline takeoffs and one #8 for a smoother mainline split.

 

 

Paul

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Posted by ROBERT PETRICK on Wednesday, May 10, 2017 9:39 AM

Has anyone done an actual, detailed study of what the model manufacturers offer as #4 or #5 or #whatever turnouts? I mean with micrometers and laser calibrators and whatnot. NMRA RP-122 notwithstanding, it seems that some store-bought turnouts use the same #4 frog but increase the radius of the diverging track and call the new thing a #6. Or a #6 a #8. Or whatever.

Peco has eschewed numbering altogether and calls their turnouts small, medium, or large. Perfectly reasonable and descriptive, but some folks might want exactitude.

I'd be curious to see if such a study or report exists.

Robert 

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Posted by riogrande5761 on Wednesday, May 10, 2017 10:00 AM

In practical terms, the bigger the turnout number, the longer the railcars you can run through them without problems.

As a teen, I learned this when I was trying to run my Athearn blue box SD45 through #4 turnouts and found out it didn't like them at all.  We didn't have as much choice back then, but I pretty much have stuck with #6 since then as a minimum.  Oh, I model 70's and 80's so yes, 6 axles diesels and long freight cars are included.

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Posted by cuyama on Wednesday, May 10, 2017 10:31 AM

ROBERT PETRICK
it seems that some store-bought turnouts use the same #4 frog but increase the radius of the diverging track and call the new thing a #6. Or a #6 a #8. Or whatever.

I have not seen that, but it might be true for some obscure supplier. The frog numbers are typically accurate -- with the notable exception of the Atlas HO and N scale (Code 80) "#4", which is actually a #4½ (and thus, not quite as sharp). What happens on the diverging leg past the frog can vary from manufacturer to manufacturer.

[The Atlas N Code 55 frogs are accurate as listed.]

ROBERT PETRICK
Peco has eschewed numbering altogether and calls their turnouts small, medium, or large. Perfectly reasonable and descriptive, but some folks might want exactitude.

This is true for PECO N Scale and for PECO HO Code 75 and Code 100, but the newer PECO HO Code 83 is accurately defined by frog number. PECO N scale Code 55 uses a #6 frog for all the turnouts, but the curved diverging leg has different radii for Small Medium, and Large, for example. PECO HO Code 75 and 100 typically have a #4½ frog, again with different diverging radii past the frog. So they are “exact”, but the curved diverging leg is the determining factor.

Barry B
What is the difference between a #4 turnout and a #5 turnout?

The first is that, generally speaking, the larger the frog number, the longer is the turnout itself. So smaller frog numbers are often chosen in tighter spaces. The exact length varies from supplier to supplier -- and pre-fab turnouts can often be trimmed a bit.

The second (and more important) is that the lower the frog number, the sharper the effective curve through the turnout. That means that longer cars and engines will be less likely to derail running through a #5 than through a #4.

For this reason, it's a good idea to match the turnout frog to the minimum radius elsewhere on the layout. To take an extreme, there's no point in using #8 turnouts with 18" radius curves in HO -- the curves will restrict the equipment that can be run.

As a general rule of thumb for HO, the tightest point through various frogs is:
"True" #4 is roughly equivalent to 14"-15" radius
Atlas "#4" (actually #4½) roughly equivalent to 18"-19" radius
#5 roughly equivalent to 24"-25" radius

These calculations are from a series of datasheets published by the National Model Railroad Association. An out-of-date link was given above, the newer version of the website is a downloadable zip archive of .pdf files found at this link:

http://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-12s_pdf_files_12.1_to_12.54.zip

[This is kind of cumbersome and I wish the NMRA had published these as individual web pages as before. The critical dimension is (11), which is the tightest curve through the frog.]

To the original poster, more information about your scale, the type of equipment you'd like to run, etc. will help others help you. Good luck with your layout.

Byron

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Posted by 7j43k on Wednesday, May 10, 2017 11:19 AM

Here is a drawing of a frog:

 

 

It is what defines the "number" of a track switch.  The "number" is derived from choosing an arbitrary distance between the "point rails" (which are NOT related to the movable points of the track switch) over to the right and finding how many times that divides into the distance between either point chosen and the "theoretical point of the frog" (back to the left).  As we all know, they can be blunt (#4) or sharp (#20).

Railroads have a huge tendency to continue the frog point rails in a long straight line as far as they can.  The longer they are, the less likely there will be a derailment or other irritations.

In the real world, people have been known to choose a point on the diverging frog rails that is the length of their shoe, and walk towards the frog point.  The number of "shoes" will indicate the frog number.  Of course, that is considered by many to be unsafe, but it does give you a visual of the ratio.

As mentioned above, you can measure a model one.  Choosing a Walthers Code 83 #10 switch, I chose an arbitrary point "a ways" out from the frog (being sure by sighting down the rails that the two appropriate rails remained straight after the frog).  I measured the width between THE RUNNING SIDES of the two rails and got .338".  From that point I measured back to the theoretical point of the frog (the real one on this sample being kinda blunt) and got 3.39".  Dividing, we get a frog of #10.03.

Frogs are almost always "straight", rather than "curved".  Both in the model and the real world.

 

Ed

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Posted by peahrens on Wednesday, May 10, 2017 6:28 PM

7j43k
Here is a drawing of a frog:

Here's another drawing of a frog.  (Steve started it.)

https://s-media-cache-ak0.pinimg.com/originals/b8/ea/56/b8ea562f15be0f3298fe733e2dbf539e.gif

 

Paul

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Posted by 7j43k on Wednesday, May 10, 2017 6:51 PM

peahrens

 

 
7j43k
Here is a drawing of a frog:

 

Here's another drawing of a frog.  (Steve started it.)

https://s-media-cache-ak0.pinimg.com/originals/b8/ea/56/b8ea562f15be0f3298fe733e2dbf539e.gif

 

 

 

Well, yeah.  But is it a #4 or a #20.  THAT'S the problem we're thrashing out here.

 

Ed

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Posted by ROBERT PETRICK on Wednesday, May 10, 2017 10:51 PM

cuyama
I have not seen that, but it might be true for some obscure supplier. The frog numbers are typically accurate -- with the notable exception of the Atlas HO and N scale (Code 80) "#4", which is actually a #4½ (and thus, not quite as sharp). What happens on the diverging leg past the frog can vary from manufacturer to manufacturer.
 

 
Okay, good. So, somebody somewhere has checked various manufacturers' offerings against NMRA (and AREA) specs for accuracy. Glad to hear that.
 
cuyama
 

Yes, this is what I was referring to. The majority of my direct experience is with N Scale, and I have used PECO Code 55 Streamline track and turnouts for well over 15 years. I'm okay with designating their turnouts using the small-, medium-, and large- scheme, but that just doesn't sound very railroady, so I'm calling my medium- and large-radius turnouts #6 and #8 respectively. Mainly because that's what they appear to be as trains pass through them.

I'm nit-picky about a lot of things but the slightly non-prototypical appearance of my PECO trackage and turnouts is not one of them. That stuff is well-made and very reliable. And by the way . . . PECO kinda plays a cover card in their advertising by calling their Code 55 flextrack visible Code 55. It appears to be about Code 75 rails with a double flange arrangement along the bottom.

Robert

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Posted by 7j43k on Wednesday, May 10, 2017 11:10 PM

ROBERT PETRICK
I'm okay with designating their turnouts using the small-, medium-, and large- scheme, but that just doesn't sound very railroady, so I'm calling my medium- and large-radius turnouts #6 and #8 respectively. Mainly because that's what they appear to be as trains pass through them.

 

 

 

We've discussed how to be railroady.  

That doesn't give you license to call them #6 or #8, unless they are.

It is a very simple concept.

 

Ed

 

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Posted by cuyama on Wednesday, May 10, 2017 11:29 PM

ROBERT PETRICK
Okay, good. So, somebody somewhere has checked various manufacturers' offerings against NMRA (and AREA) specs for accuracy. Glad to hear that.

That's not what I posted -- I said that the frog numbers are generally accurate. The overall dimensions vary greatly from supplier to supplier, as I said. And NMRA and AREA specs differ from each other.

ROBERT PETRICK
so I'm calling my medium- and large-radius turnouts #6 and #8 respectively

Personally, I wouldn't, since it's not accurate. But I'm not building your layout. Smile

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Posted by mlehman on Thursday, May 11, 2017 3:35 AM

If we're going to be nitpicky, there are regular turnouts, which have a straight diverging track after the frog, and curved turnouts, that have curved stock and diverging tracks.

The idea that a turnout's diverging track is curved comes in part from two things. One, a few model turnouts have a straight through stock track, but a curved diverging track. Two, the talk of effective radius, which is good to know, but doesn't necessarily mean there is a curved diverging track. Plus the points leading into the frog are curved, but what's past the frog usually isn't with a standard turnout.

 

Mike Lehman

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Posted by ROBERT PETRICK on Thursday, May 11, 2017 8:21 AM

Can we look at this from another angle (as it were)?

I just got a shipment from MBKlein (another thread) and included were some PECO N Scale Code 55 Streamline stuff. I'm interested in two things in particular: one is labeled "large-radius turnout" and the other "medium-radius turnout". I took the things out of the plastic wrapper and measured each from apparent point of switch to apparent point of frog. I used a Starrett machinist rule and a (fairly-well) calibrated 60-year-old eyeball. I got 4.61" for the first and 3.65" for the second. Based on these measurements alone, what should I call these things?

Thanks.

Robert

 

EDIT  In the meanwhile, I'm gonna download and read the link Byron provided. It is a zip file, and I could not read it yesterday on my cell phone.

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Posted by carl425 on Thursday, May 11, 2017 9:10 AM

ROBERT PETRICK
Based on these measurements alone, what should I call these things?

Peco chose to disregard prototype practice and do their own thing (not that there's anything wrong with that).  There is therefore no name for them using prototype vocabulary.  You should call them "Peco large-radius turnout"  and "Peco medium-radius turnout".

I have the right to remain silent.  By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.

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Posted by 7j43k on Thursday, May 11, 2017 10:11 AM

ROBERT PETRICK

Can we look at this from another angle (as it were)?

I just got a shipment from MBKlein (another thread) and included were some PECO N Scale Code 55 Streamline stuff. I'm interested in two things in particular: one is labeled "large-radius turnout" and the other "medium-radius turnout". I took the things out of the plastic wrapper and measured each from apparent point of switch to apparent point of frog. I used a Starrett machinist rule and a (fairly-well) calibrated 60-year-old eyeball. I got 4.61" for the first and 3.65" for the second. Based on these measurements alone, what should I call these things?

 

 

 

You are doing it wrong.

Below is a picture of a Peco switch:

 

 

You can see the frog over on the left.  Measure it in the way I described earlier.  That will reveal the frog number.

In simple words:  for the above, measure the width and the length of the outside dimensions of that sharp pointy thing on the left and divide.

 

 

Ed

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Posted by ROBERT PETRICK on Thursday, May 11, 2017 10:45 AM

7j43k

You are doing it wrong.

In simple words:  for the above, measure the width and the length of the outside dimensions of that sharp pointy thing on the left and divide.

Ed

Hey Ed-

Yes, I am doing it wrong. I am measuring the switch lead and not that sharp pointy thing on the left. The lead is an important dimension in the geometry of a turnout. My contention is that Peco uses #6 frogs for all their turnouts. And as cuyama and others have pointed out, what happens downstream on the diverging route varies from manufacturer to manufacturer. My initial question was whether anyone has studied these discrepancies. My secondary question is what should I call my things. Calling them a number-seven-and-a-quarter-turnout-with-a-mismatched-ragged-number-six-frog is a bit cumbersome. And calling them a large-radius turnout is a bit dull.

But thanks for your imput.

Robert 

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Posted by cuyama on Thursday, May 11, 2017 11:41 AM

carl425
call them "Peco large-radius turnout"  and "Peco medium-radius turnout".

+1

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Posted by DSchmitt on Thursday, May 11, 2017 12:10 PM

cuyama

 

 
carl425
call them "Peco large-radius turnout"  and "Peco medium-radius turnout".

 

+1

 

That's what PECO calls them   http://www.peco-uk.com/

 

I tried to sell my two cents worth, but no one would give me a plug nickel for it.

I don't have a leg to stand on.

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Posted by 7j43k on Thursday, May 11, 2017 12:19 PM

ROBERT PETRICK
Hey Ed-

Yes, I am doing it wrong. I am measuring the switch lead and not that sharp pointy thing on the left. The lead is an important dimension in the geometry of a turnout. My contention is that Peco uses #6 frogs for all their turnouts. And as cuyama and others have pointed out, what happens downstream on the diverging route varies from manufacturer to manufacturer. My initial question was whether anyone has studied these discrepancies. My secondary question is what should I call my things. Calling them a number-seven-and-a-quarter-turnout-with-a-mismatched-ragged-number-six-frog is a bit cumbersome. And calling them a large-radius turnout is a bit dull.

But thanks for your imput.

Robert 

 

 

Robert,

Glad to be of service.

I am glad that you have fleshed out your concerns.  They haven't been clear up to now.

To your first question:  Someone first has to CLAIM or ESTABLISH discrepancies before they can be investigated.  I don't recall any such, but I/we might have missed them.  Nor do I (we?) recall any investigations.  So it looks like you are the first one to do so.  Therefore the answer would be, up to now: No.  But see below.

 

I downloaded from here:

http://www.peco-uk.com/page.asp?id=pointplans

photographs of N gage code 55 Electrofrog turnouts.  I measured the frog sizes:

 

small--#5.1

medium--#5.65

large--#6.6

So, no, they don't use the same #6 frog on all three.

 

My first thought on what to call them would be #5, #5 1/2, #6 1/2.  If that's too cumbersome, you could go with #5, #6, and #7.

Problem solved, I think.

 

Ed

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Posted by cuyama on Thursday, May 11, 2017 12:34 PM

7j43k
So, no, they don't use the same #6 frog on all three.

I have the physical Code 55 turnouts myself, and they all seem to be the same frog. It would be strange to engineer products with such tiny differences in frog numbers, it seems to me.

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Posted by 7j43k on Thursday, May 11, 2017 12:42 PM

I checked my measurements and found I was wrong on the small one.

Corrected:

 

small--#5.7

medium--#5.65

large--#6.6

 

So then I would call them #6S, #6L, #7

Apolgies for the error.

Ed 

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Posted by cuyama on Thursday, May 11, 2017 12:51 PM

7j43k
So then I would call them #6S, #6L, #7

One could name them Larry, Moe, and Curly -- but it wouldn't change what the manufacturer (and every other modeler) calls them. I don't see any good reason to add confusion, personally.

 

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Posted by cuyama on Thursday, May 11, 2017 1:07 PM

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Posted by ROBERT PETRICK on Thursday, May 11, 2017 1:37 PM

Sorry for causing so much consternation.

At least I've found something regarding my initial question. It seems somebody has investigated model dimensions vs prototypical dimensions:

NMRA Geometric Design

As for the other, I'll go with the dull Peco nomenclature. Sad

Robert

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Posted by 7j43k on Thursday, May 11, 2017 2:28 PM

Robert,

Consternation frequently leads to knowledge, so I will be thanking you.

I do not work in N.  I had no idea how "free form" some N scale trackage was.  Now I do.  My assumption that HO track switches are (close to/trying to be/are) NMRA correct will not be automatic, anymore.

And I especially appreciate your finding the NMRA document.  I expect to be hand building some switches in the future, and I'll take all the help I can get.

 

Ed

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Posted by gregc on Thursday, May 11, 2017 3:36 PM

after hand laying turnouts, i looked at Variations in turnout dimensions.   The frog number describes the angle at the frog, not a distance.

the following diagram illustrates how NMRA turnout dimensions appear inconsistent depending on frog number.   The red closure rail is drawn with the proper prototype radius (see Catskill below) indicating where the frog should be located.   Most seem short (see bottom plots).

The Catskill Archive describes how prototype turnout dimensions are calculated (show below).

The radius (leftmost number) between the points and frogs can vary leading to various length (middle number) turnouts that are all the same frog number.  Blue section of closure rail is curved and red section is straight.

The key dimensions describe the distance between the points and frog.  That distance, the length of the diverging rails and those preceding the points may vary between manufactures and all be the same frog number.

greg - Philadelphia & Reading / Reading

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Posted by 7j43k on Thursday, May 11, 2017 3:47 PM

More neat info!

 

Thanks, Greg

 

Ed

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Posted by rrinker on Sunday, May 14, 2017 12:12 PM

 Doesn't seem like anyone mentioned, but the angle oof the frog is Arctan(1/frog number). So a #6 angle is arctan(1/6) or 9.46 degrees, and a #4 is arctan(1/4) or 14 degrees. All derived from the definition of the various Trigonometry functions and the basic fact that the frog number indicates how far along (adjacent side) you go to get 1 unit (the opposite side) apart. Since Tangent of the angle is opposite over adjacent (in the case of a #6, 1/6), then the angle by definition is the inverse tangent (arctan) of opposite over adjacent. Those that had Trig may remember SOHCAHTOA - Sine = opposite/hypotenuse, Cosine = adjacent/hypotenuse, and Tangent = opposite/adjacent.

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Posted by 7j43k on Sunday, May 14, 2017 2:32 PM

9.46 degrees is 9 deg 27.6 min.

For a #6 frog:

If the frog angle is based on measuring back to the frog point from the midpoint of the line that forms the "1 unit" location, one gets 9 deg 32 min.*  See: 

http://www.pcrnmra.org/pcr/clinics/Kolm-TurnoutsWhatYouNeedtoKnow-PCR2008-handout.pdf

If the frog angle is based on measuring back along either rail to the frog point at the "1 unit" location, one gets 9 deg 34 min.

 

While pokin' around, I found this neat item on trackwork:

 

http://www.engr.uky.edu/~jrose/RailwayIntro/Modules/Module%206%20Railway%20Alignment%20Design%20and%20Geometry%20REES%202010.pdf

 

Ed

 

* Calculations deriving 9 deg 32 min for #6 switch:

tan x = .5/6

x = 4 deg 46 min

frog angle = 2x = 2 (4 deg 46 min) = 9 deg 32 min

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