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page trail:  Templot Club > Forums > Trackbuilding topics > Wheel drop at the vee
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                                       Wheel drop at the vee
     
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1st message | this message only posted: 22 Nov 2015 21:18
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from:
DerekStuart
United Kingdom

 

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Hello fellow Templotters
I have followed the 00sf/4sf thread in "the other place" and with what I learned, I made some very smooth crossings that- to my eyes- looked right and showed no sign of any wheel drop. (I am doing this in P4, but the same rules apply).
However, after referring to NER-A books I found that my knuckle bends were still too sharp, so I tried to make them more gentle.
A 1:8 knuckle bend comes out with a bend very similar to the circumference of a Scalefour mug. So I bent the rail around that, carefully checking until the straight parts lined up with the stock rail and the wing rail of a Templot diagram (I put 0 flare on the wing rail and extended them considerably so that I would have something more to align them on). As a point of note, the curve should be even more gentle than the mug.
I put a very slight taper on the nose of the vee and blunted it to .25mm and tack soldered. Now I have found that the wheel is dropping into the knuckle- not a lot and it is still supported on the outer edge, but only just. The curve is also starting a little way before the X chair rather than AT the X chair as per the diagram.
I was wondering if this might be a problem of trying to put an exact geometry with the "far too coarse and overscale" flangeways of P4. In effect to open up the flangeways to .68mm rather than .58 I have caused the knuckle to be .2mm too long or too wide.
I must admit that it LOOKS wrong too- I've never seen a turnout (even NYMR, Beamish, Wensleydale) that has such gentle curves.
Any comments would be appreciated. I certainly don't want to go back to using the sharp bend that you can produce on the S4 jig! Many thanks.

Derek
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2nd message | this message only posted: 22 Nov 2015 21:59
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Martin Wynne
West Of The Severn, United Kingdom



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Hi Derek,

The widest part of the crossing gap is immediately in front of the blunt nose. That's 2 flangeway gaps plus the blunt nose width. Your wheels must be wider than that. For P4 with overscale flangeways that is 2 x 0.68mm + 0.25mm = 1.61mm. Wagon wheels are usually 5" wide, which scales to 1.67mm, so only just wide enough to span the gap. In fact not quite wide enough if you allow for the corner radius on the rail and a chamfer between the face of the wheel and the tread.

If you use exact scale wheels you need to make sure not to exceed the specified flangeway gap just in front of the nose of the vee.

Here's some stuff I have posted on RMweb a few times:
__________________________

The knuckles should be radiused, the knuckle gap being wider than the crossing flangeway gap.

Here's a diagram which may help when setting the wing rail knuckles:



The blue infill shows the theoretical ideal with a sharp bend at K exactly matching the angle of the vee and in line with it. In practice on the prototype it is not possible to make such a sharp bend because of the 1:20 inclination of the rails.

Instead, a short curve is used, as shown by the green line, making the knuckle gap wider than the flangeway gap. It works fine, and can help if replicated on the model. Some companies made this curve quite gentle and obvious as shown -- the NER for example. On the GWR the curve matches the crossing angle in feet, so for example a 1:7 crossing has the knuckle bend curved at 7ft radius.

But it's important to get the flangeway gap correct alongside the nose of the vee at X in the diagram, otherwise there is a risk of wheels dropping into the gap in front of it.

What you must not do is make the knuckle bend too sharp, as shown by the red line. This is guaranteed to cause problems.



regards,

Martin.

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3rd message | this message only posted: 22 Nov 2015 22:26
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from:
DerekStuart
United Kingdom

 

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Thanks Martin. That is really good of you to post that, although I have seen that before (linked from your 00-sf thread).

I will go back to it tomorrow and measure as you have suggested. I am aware of those facts (the 00sf/4sf threads explained it quite well) which is why I am puzzled what I have done wrong. I will re-measure it.

Thanks
Derek
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4th message | this message only posted: 4 Sep 2017 19:49
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from:
Andrew Duncan
Reigate, United Kingdom



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Hello Martin
I've only now come across this thread which interests me. You say...
 
"What you must not do is make the knuckle bend too sharp, as shown by the red line. This is guaranteed to cause problems." 
 

I am interested in this as I'm up to my neck in crossings of one kind or another for Yeovil Pen Mill and am bending the knuckles just with parallel jawed pliers which give a much sharper radius than the one shown in the drawing. So whilst the Great Western may not have used such a gentle radii, I'm wondering if I might improve the running qualities if I tried to produce a gentler bend? If so do you have any recommendations as to how to do it?
 
Kind regards
Andrew

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5th message | this message only posted: 4 Sep 2017 22:09
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from:
JFS
United Kingdom

 

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Hello Andrew,

We did discuss this at Scaleforum - amongst a million things...  On the real thing, the radius of the vee in feet was equal to the number of the crossing - ie a 1:9 crossing would have wing rails bent to a nine foot radius - which is pretty gentle!  I tend to make the bend in two parts - the first a mm or so to one side of the intended "bend", taking the rail half way there, the second a mm or so to the other side to finish the job off. 

Templot templates show the radius as it should be so you can test the result against the template, but we are not looking for exactitudes here - certainly not in your chosen gauge(!).

If you make the crease too sharp (and I have seen all kinds of horrors suggested as means to that pointless end) you create the certainty that the back of the flange will strike the inside of the opposite wing rail - exactly not what we want.

Hope that helps.

Best wishes,

Howard

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6th message | this message only posted: 4 Sep 2017 23:53
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Andrew Duncan wrote:I am interested in this as I'm up to my neck in crossings of one kind or another for Yeovil Pen Mill and am bending the knuckles just with parallel jawed pliers which give a much sharper radius than the one shown in the drawing. So whilst the Great Western may not have used such a gentle radii, I'm wondering if I might improve the running qualities if I tried to produce a gentler bend? If so do you have any recommendations as to how to do it?Hi Andrew,

Making symmetrical bends is quite difficult using pliers. My method of making radiused bends in rail is to improvise a v-press arrangement. It's easy to do and costs nothing:



Trial and error with the diameter of the bar and spacing of the supports, until you get consistent results. Usually something can be found of the right size, such as an old battery. It needs to be smaller than the desired knuckle radius because of the spring in the rail.

Perhaps also add some packing below the rail as a depth stop.

I don't believe the knuckle radius is too critical in terms of running, provided the wing rail front aligns properly with the vee rails and the check rails are correctly positioned. But now that Templot templates show the extent of the knuckle bend, you have something to aim for in making a prototype pattern knuckle. 

For sharply defined bends, such as the set in the switch stock rail, practice with a small hammer:



regards,

Martin.

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7th message | this message only posted: 5 Sep 2017 03:51
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from:
Andrew Duncan
Reigate, United Kingdom



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Hello HowardThanks for your reply (swipes at us poor souls who don't/can't model to the ultimate gauge, aside) and clear explanation of the radii required. I'll give your solution a try and if or when it fails I'll try Martins somewhat more scientific approach!
I trust everything's going well in your preparations for Scaleforum and hope to see you then. 
Kind regards 
Andrew

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8th message | this message only posted: 5 Sep 2017 04:15
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from:
Andrew Duncan
Reigate, United Kingdom



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Hello MartinThanks for your answer to my question and clear diagrams that supported it.

 One thing I forgot to ask you originally is do you try to put a subtle enlargement in radii in the top of the rail to take the 20 degree cant into account? I've been trying to fudge this by bending up the closure / wing rail to fit, loading the closure rail up to the knuckle with chairs, (I break the rail at the heel not closer to the V as is more usual ) placing the assembly on a flat surface and sighting it from the side to see how far up in the air the far end of the wing rail sticks up. Then putting the assembly in a vice and bending it down a smidgen. 

I aware that this approach is crude and doesn't address the cant remaining at 20 degrees along side the V. Have you got any neat tricks to overcome this problem?
Andrew

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9th message | this message only posted: 5 Sep 2017 11:14
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Hi Andrew,

I don't believe it is possible to put a truly conical bend in rail using ordinary modelling hand tools. For the head of the rail to run round a larger radius than the foot, the head must be stretched in length relative to the foot. In order to do that you would at the very least first need to anneal the rail at red heat to fully soft condition. Short of building a substantial precision press tool which can grip the rail while it is being bent.

All you can do is make the bend normally and then twist the rail back down level, as best you can.

Even the prototype has difficulty holding wing rails down flat alongside the nose of the vee. But they do have the advantage of heavy chair castings, spacer blocks and bolts. Expecting a soft plastic chair to do the same with model rail is asking a bit much.

Traditional model track building on Brook Smith rivets or copper-clad uses vertical rail. That does make it a lot easier to build precisely aligned switches and crossings.

regards,

Martin.


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10th message | this message only posted: 5 Sep 2017 11:38
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from:
Martin Wynne
West Of The Severn, United Kingdom



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p.s.

In EM and 4-SF (00-SF) at around 1:6 to 1:8, the knuckle coincides with the "X" chair.

So you could try making a saw cut through the foot of the rail up to about half the rail height, and then making the knuckle bend. This would allow inclined rail to follow the head radius.

The cut would be hidden by the chair after assembly.

That's not feasible in P4, where the knuckle comes between the "A" and "X" chairs at those angles. A cut in the bottom of the rail would be visible and look bad. You could maybe shove the "X" timber an inch or two, and not tell anybody. :)

At around 1:9 to 1:10 the advantage switches to P4.

Martin.

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11th message | this message only posted: 5 Sep 2017 13:35
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from:
JFS
United Kingdom

 

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Andrew Duncan wrote:  (swipes at us poor souls who don't/can't model to the ultimate gauge, aside)
Moi?  :)   ... and not that P4 is in anyway "ultimate" - just less of a compromise!

I think it would be easy to over-complicate these things - as long as the bend is a reasonable radius, it will work. And plenty of track has been built - even in 18.83 - with such things done incorrectly, and mostly it works...  The simple fact that you are concerning yourself with such things tells me you will find the way which works for you.

My solution to the 1:20 issue is to thread some chairs onto the closure rail (I always make my closure and wing rails in one piece for this reason) sit the assembly down on its the chairs, and then twist the rail at the knuckle until the wing rail comes back something like horizontal. If a vertical bend remain, you can put the wing rail edge-on in a vice and tweak it back into line.
As Martin says, it is a bit of a "best you can" job, but provided the final alignments are alright and the rail is not trying to fight the chairs,  all will be well. But if the rail is pulling at the chairs you will have problems later. And if the wing rail is not twisted back down, it will throw your levels out somewhere or other.
I have had one or two which have put up a fight and ended up in the scrap, but it only takes a minute or two to make another.

Personally, I would not be keen on cutting the rail - such things introduce a weakness which I find can then present issues.

I do see a lot of track where the wing rail and closure rails have been made separately and where the alignment is obviously poor at the resulting joint - and it is a bad fault because it throws the wheels just on the approach to the crossing leading to very poor running.

See you (and Martin?) at Scaleforum!

Best wishes,

Howard



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12th message | this message only posted: 5 Sep 2017 16:08
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Tony W
North Notts., United Kingdom

 

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Hi Andrew.
The standard advice for many years has been to produce a sharp bend, which as this thread and others have explained is just plain wrong. I discovered this the hard way.
I use a similar technique to Howard to produce an approximate bend but using a small vice. I mark the top of the rail with a wide felt tip pen, which I try to centre on the bend. I then put the rail in the vice with one edge of the mark lined up with the side of the jaws and half bend. Then move the rail to the other side of the mark and repeat the process. It is a simple matter to adjust this bend between ones fingers if it is out. The exact radius is less important than the fact that there is one.
On the prototype the Crossing Flangeway is 1 3/4" wide, but for a 1 in 8 crossing the knuckle gap is 2 1/4" noticeably wider. The knuckle gap dimension varies with the crossing angle.  As a quick way to check a crossing, insert the Crossing Flangeway gauge into the knuckle gap. It should be a loose fit. Not accurate I admit, but as a rough and ready check it works. If the CF gauge is tight you have a problem, which is often what happens when sharp bends are used.
The crossing area of any formation is the most critical part and pays dividends for time spent making sure they are right.
Regards
Tony.

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13th message | this message only posted: 5 Sep 2017 21:59
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from:
Andrew Duncan
Reigate, United Kingdom



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Thank you Martin, Howard and Tony for your various helpful advises. It makes me feel less alone and not not quite so much of a bodger as I thought. Its also very good to gain a greater understanding of the prototype and how you've all solved the problem for yourselves.
Regards
Andrew



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