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topic: 1061Curved Diamond
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posted: 7 Mar 2010 01:48

from:

allanferguson
 
Fife - United Kingdom

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I  have  a  double  junction  at  one  end  of  my  station  (think  Gleneagles!),  and  I'm  anxious  to  keep  the  curvature  through  the  diamond. Just  to  complicate  matters  there's  a  slew  on  the  main  line  as  well.  Now  I  cannot  for  the  life  of  me  work  out  how  to  draw  the  diamond  in  Templot  (I  can  usually  suss  things  out  eventually,  but  haven't  managed  this  one!).  I  can,  and  have  in  the  past,  built  the  track  on  the  template,  making  the  various  crossings  to  suit.  But  I'm  sure  it  can  be  done  more  sophisticatedly.  I  don't  want  to  change  any  of  the  existing  alignments,  as  I  struggled  for  a  long  time  to  get  the  whole  thing  to  flow.  Ignore  the  timbering -- I'll  be  using  interlaced  sleepering  a  la  Caledonian  Railway.  Can  anyone  advise  me?  Please!

Allan  Ferguson
Attachment: attach_746_1061_Muckhart_north_10_03_07_0124_09.box 318

posted: 7 Mar 2010 08:48

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Hi Allan,

It's not generally a good idea to run a slew through pointwork -- slews are intended mainly for plain track. If possible it is better to use a transition curve instead. I found that this transition matched your alignment very closely:

initial radius = 10980 mm
final radius = straight
length along the initial radius = 0
length along transition section = 995 mm

2_070316_330000000.png2_070316_330000000.png


I snaked (CTRL+F6) the turnout forward by about 2mm to line up the V-crossing with your existing track:

2_070317_110000000.png2_070317_110000000.png


The diamond-crossing is an irregular diamond, meaning that the radii in the two roads differ. This means that all the crossing angles also differ. Irregular diamonds are not (yet) supported in Templot.

Instead, you would need to create it using partial templates. This is an example of such an irregular diamond which you can download and examine:

irreg_double_junct.pngirreg_double_junct.png

Download from (right-click):

 http://www.templot.com/samples/irreg_double_junct.box

Some notes about this design at:

message 1640

regards,

Martin.

posted: 7 Mar 2010 15:08

from:

Dellboy
 
Aylesford - United Kingdom

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Martin

How did you determine the 48.67mm spacing between the tracks?

Derek

posted: 7 Mar 2010 15:16

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Dellboy wrote:
How did you determine the 48.67mm spacing between the tracks?
Hi Derek,

It's the equivalent of 7ft way, i.e.1ft increase on the minimum 6ft way to allow for vehicle overhang on the curves. Just a guess, but it's usually enough.

I haven't forgotten your video showing how to check such curves for adequate clearance. :)

regards,

Martin.

posted: 8 Mar 2010 10:39

from:

allanferguson
 
Fife - United Kingdom

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Martin Wynne wrote:


The diamond-crossing is an irregular diamond, meaning that the radii in the two roads differ. This means that all the crossing angles also differ. Irregular diamonds are not (yet) supported in Templot.

Instead, you would need to create it using partial templates. This is an example of such an irregular diamond which you can download and examine:

Many  thanks,  Martin,  for  your  very  prompt  and  comprehensive  response.  I'll  have  a  think  about  it!  I  do  feel  a  certain  sense  of  misplaced  pride  to  have  found  something  that  Templot  can't  do -- it's  usually  me  that  can't  do.....

A  thought  occurs.  On  the  real  railway,  where  this  sort  of  junction  was  not  unusual,  how  did  they  lay  it  out,  given  that  the  special  chairs were  made  in  a  finite  range  of  angles?

Regards

Allan  Ferguson

posted: 8 Mar 2010 11:05

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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allanferguson wrote:
A thought occurs. On the real railway, where this sort of junction was not unusual, how did they lay it out, given that the special chairs were made in a finite range of angles?
Hi Allan,

There are two approaches to traditional double-junction design.

The early method, for most of the pre-grouping period, was to lay out a ruling curve radius through the diamond, calculate the various crossing angles, choose the nearest available chairs, and fair them into the ruling curve as best they could be made to fit.

Prototype radii tend to be much easier than on our models, so this method isn't as clunky as it sounds. The actual errors may be no more than a 32nd of an inch, and normal traffic wear soon removes any rough edges.

The later method, applicable to the post-nationalization era, is to establish the nearest available crossing angles as above, and then to redesign the diamond so that these angles fit exactly. That requires using a slightly different radius for each rail leg between each crossing, instead of having a single ruling radius through the whole thing. A range of standard double junctions was available, to be used where they will fit and avoid the need to do a complete design every time.

Modern FB uses cast crossings, made to exactly match the required radius and angle.

regards,

Martin.



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