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                 Rail curve in the middle of straight diamonds
     
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1st message | this message only posted: 9 Dec 2020 17:26
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from:
Julian Roberts
 

 

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Hi Martin
I believe it was just a few years ago, say within the last five, that you brought in the three marks on the curve of the wing/knuckle rail at the knuckle on an ordinary turnout.  Yet not so many years ago I was told elsewhere that the knuckle bend should be as crisp as possible, aided with a nick filed on the other side of the rail. My understanding of this area has developed, maybe that holds true for others too.  I imagine the consensus would be that the model will work better (as well as look better) by following the prototype practice - or at least, there is no need to follow old modelling myths.

Now I'm making a diamond and wonder about a similar issue at the centre of it, where the stock rail and check rail curve to form the angle of the obtuse crossing.  It seems that on the prototype these rails curved quite gently - at least on the 1: 7.5 crossing I'm making.  

Someone on the Scalefour Forum sent a picture of a drawing for this area - here it is. 




The radius is marked, roughly track gauge, extending over a greater length than the sleeper width.  Meanwhile the printout from my Templot template shows a curve, but not one as long and gentle as that, though it is difficult to say where it begins and ends - just the useful thing about the three marks on turnout acute crossings. 



 Here is a screenshot of the Templot trackpad for the same thing, showing a crisp bend.





So I'm wondering a few things about this.

First, is there a good modelling reason not to emulate the prototype?  Dave Bradwell on the Scalefour Forum suggested that making the knuckle bend crisp will help flanges not to go the wrong way on such a flat crossing in P4.  This seems completely credible, and I wondered if that is the reason Templot doesn't show a prototypical gentle bend.

Second, what I think is the most interesting thing - why does the prototype do what it does?  Surely the same considerations would apply as the crossing became flatter?  Or maybe this drawing is not typical of all companies or the standard REA ones?  Inversely to the previous question, might there be a good modelling reason to follow the prototype, that we haven't thought of, or haven't tried?

Third, maybe this is just not important enough for you to have incorporated it, just as it was only relatively recently that you brought in the acute crossing three marks.  Improving the clarity of the NLS map when making a trackplan, for example, is I'm sure a much more widely useful upgrade.

Just to be clear, I'm not asking this because of the look of the thing, but because of actual running. In P4 there is at least in theory an issue of the wheels going the wrong way at a less flat angle than S4 and the prototype, and good running seems to rely on perfect alignment but with a risky short length where the wheelset is unchecked.

I hope it won't seem I'm complaining! - Not at all, it is just a point of interest I hope you'll agree!

Cheers
Julian



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2nd message | this message only posted: 9 Dec 2020 18:20
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from:
Paul Boyd
Loughborough, United Kingdom

 

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Hi Julian
Dave Bradwell is a modeller I respect, but I’m puzzled as to why he thinks a crisp bend would stop the wheels going the wrong way.  The check rails do that, and there is no unchecked length!  This is really the only railway modelling forum I follow, and so I haven’t seen any of the shenanigans on other forums!

I model in P4 and aim for a curve - the rule of thumb I use is to bend the rail over round nose pliers!  I’m sure there’s a more prototypical formula though.

I suspect the reason that Templot shows a sharp bend is simply down to programming, plus I find that the sharp bend is a good indication of where the centre of the curve should be.

Cheers,
Paul

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3rd message | this message only posted: 9 Dec 2020 18:54
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Paul Boyd wrote: I model in P4 and aim for a curve - the rule of thumb I use is to bend the rail over round nose pliers!  I’m sure there’s a more prototypical formula though.

I suspect the reason that Templot shows a sharp bend is simply down to programming, plus I find that the sharp bend is a good indication of where the centre of the curve should be.
Hi Paul, Julian,

The rule of thumb is that the radius in feet matches the crossing angle. So a 1:7 K-crossing has the rails bent at 7ft radius. Likewise for the knuckle gaps in V-crossings. You need to check the nose of your pliers! :)

The reason Templot doesn't show the bend radius for K-crossings is that I haven't got round to it yet. :(

It's not as simple as it looks because of course a K-crossing is composed of two separate templates.

It's not so very long ago that I introduced the proper knuckle bends showing on the V-crossings. Previously, and right from the start of Templot, I assumed users knew enough about track to know what they were doing and use the templates as a construction guide, not an actual drawing of a turnout, and make a proper radiused knuckle. The sharp bend mark was intended as an aid to locating the centre of the knuckle bend. In any event, it's not physically possible to make a bend in the rail as sharp as shown.

When I next see a knuckle with one of those awful nicks filed in the rail, it will be the required kick up the bum to get something done about it. It's been on the list for a long time. However, there is so much still to do to get 227a finished that I doubt I can do it very soon.

In answer to Julian's question, I don't believe making a sharp bend in the wing rail (the running rail) will have any significant effect on running. Keeping a sharpish bend in the K-crossing check rail may help a bit. If you have a problem, the biggest single improvement you can make is to raise the K-crossing check rail above the level of the running rails, as is done now on the prototype. For example by using code 100 rail with the foot filed off. But don't do that if you have any locomotives with flangeless driving wheels. And keep some Elastoplast handy for when rail-cleaning.  :)  

cheers,

Martin.

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4th message | this message only posted: 9 Dec 2020 21:51
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from:
Paul Boyd
Loughborough, United Kingdom

 

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Hi Martin
I have carefully measured the radii at various points on the nose of my pliers, and concluded that the radius is, oh, about right!!!  :D :D  Now you mention it, I did know about the radius/crossing angle relationship but had completely forgotten it!

I've seen the reference to filing the notch, even in BH rail, promptly dismissed it and have never done it.  It's just plain wrong!  Even on the FB narrow gauge turnouts I've just mostly completed (and put photos up yesterday), I just bent the rail as normal.  Admittedly the foot of the rail I used was not as wide as some.

But I'm intrigued...  
the biggest single improvement you can make is to raise the K-crossing check rail above the level of the running rails, as is done now on the prototype.
How does making the check rail a bit higher make a difference?  I can't work it out.

Cheers,
Paul

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5th message | this message only posted: 9 Dec 2020 23:13
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from:
Rob Manchester
Manchester, United Kingdom



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Hi Paul,
I would guess raising the check rail would mean that it was 'checking' the wheelset over a longer chord of the wheel tending to keep the wheelset more easily at right angles to the track line. Sound feasible ?

Rob


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6th message | this message only posted: 9 Dec 2020 23:59
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Hi Paul, Rob,

Remember that a check rail on one side controls what happens to the wheel on the opposite side.

A higher check rail means the wheel can roll further forward past the knuckle while still being under the sideways control of the check rail, helping to prevent the opposite wheel flange from hitting, or passing to the wrong side of, the point rail.

 Quick diagrams of that, wheelset moving left to right:



Shows only the wheel flange, rest of wheel omitted.



cheers,

Martin.

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7th message | this message only posted: 10 Dec 2020 09:48
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from:
Julian Roberts
 

 

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Hi Martin, Paul, Rob

I too couldn't see how the raised checkrail could help, till your explanation Martin. My problem with that is that in the one-fine-day drawer is a 2-10-0...

For what it's worth, my single experimental wagon with EM flanges set to roughly 17.57 can't go the wrong way on this crossing. But it remains an experiment because it rolls far less freely.

I can't see why the Dave Bradwell thing wouldn't help, as surely it would albeit minutely reduce the unchecked distance. However on my crossing as built one of the checkrails is built with as smart a change of angle as I could manage, but I don't think there is any change of behaviour resulting, compared with the other side.

On the other hand, if a 1:7 angle would by rule of thumb demand a 7 foot radius that's a lot more than the drawing I posted earlier, a much longer curve than I've made.

However I've tested all my locos through the crossing again, at different driving wheel positions, and the only one that derails at one position of the wheels has a badly overgauge BB setting of around 17.85, something I've meant for several years to remedy. Unfortunately it's otherwise one of my best locos!
Wagons go through perfectly, and I made a video of three of them propelling my Crab loco with the motor disconnected.  With its tender it weighs a good 800g, and the gradient is slightly uphill towards each end of this test track

https://youtu.be/_O0pKy8c2oo

Cheers
Julian

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8th message | this message only posted: 10 Dec 2020 10:20
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from:
Paul Boyd
Loughborough, United Kingdom

 

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Hi Martin 
Thanks for that diagram, that makes perfect sense now!

Cheers,
Paul

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9th message | this message only posted: 15 Dec 2020 17:49
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Post your questions on the forum where everyone can see them and add helpful replies.
I forgot to mention that if you use a raised K-crossing check rail in a slip, the ends of the check rail will need to be cut down to or below rail level, if it would be possible for the outer edge of a wheel running on the slip road to catch against them.

This is sometimes done on the prototype even with normal-height check rails, to allow for future wear of the slip rail.

Martin.

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10th message | this message only posted: 20 Dec 2020 21:26
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Hi Julian,

Here are the details of NER K-crossing point rails, dated August 1911:











The nose width for NER is 5/8". The top planing is 3/16".

Notice also that the foot width is reduced from 2.3/4" to 2.3/8" to fit the chair.

Note also that the angles go up to 8.1/2 for fixed K-crossings on NER. Some other pre-group companies went as far as 9.

cheers,

Martin.

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