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                                       0-MF curved points. A question of radii ?
     
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1st message | this message only posted: 2 Jun 2017 11:50
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from:
madscientist
 

 

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Oh collected gurus 

For my sins , I'm designing a large 35 feet 15 foot O gauge layout for my club and building " some " of the turnouts. As I have a lot of 00-Sf work under my belt , how hard can it be ?????!!!
Reading the  Gauge O guild trackwork handbook, they mention that the respective radii of curved points should be  1:1.5 to avoid fine angle at the " V" and potentially long leads on the switch blades , with the comment that wheel drop could occur. 

Now my space contraints mean my main line double track inner curve is at 6 ' ( sorry I'm an old money man ! ) And I need to diverge inside that to access the goods line , that divergence radius , I'd like to keep to a min of 5'6" 

I haven't temploted this yet.  But even in O-MF am I storing up issues here 

Thanks 

Dave 


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2nd message | this message only posted: 2 Jun 2017 12:53
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from:
Martin Wynne
West Of The Severn, United Kingdom



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madscientist wrote: avoid fine angle at the " V" and potentially long leads on the switch blades , with the comment that wheel drop could occur.Hi Dave,

This is the sort of utter rubbish which is still too prevalent within the hobby.

Wheel drop is caused by the flangeway gap being too WIDE, or the wheels being too NARROW, whichever way you want to look at it.

The ANGLE of a crossing, and the LENGTH from the knuckle to the vee is irrelevant.

It's true that if the flangway gap is too wide, or the wheels are too narrow, then wheel drop will occur and it will be worse for flatter crossing angles.

But if that is not the case, NO wheel drop will occur regardless of the crossing angle.

The width of the gap across between the wing rails immediately in front of the crossing nose is the SAME regardless of the crossing angle. If the wheel is wider than this, as it should be, it is physically impossible for it to fall into the gap.

You have ensured that your wheels will be wider than that gap by adopting the 0-MF standard, so you can safely build curved turnouts as long as you like.

The note about switch blades is also misleading. They are no longer in a curved turnout than in the same sized straight turnout.

It's true that if folks draw simple curved templates by hand using tangential radii they will create some unnecessarily long thin switch blades. This also happens in the Trax program for example in creating curved turnouts. I often see curved turnouts on exhibition layouts where the switch blades are far too long and could sensibly have been shortened if prototype designs had been followed.

If you create your curved turnouts for 0-MF in Templot, you won't have any problems.

See for example:

 http://www.westernthunder.co.uk/index.php?threads/heyside-7mm-l-y-late-50s-early-60s.552/page-62#post-118358

(70 pages).

regards,

Martin.        

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3rd message | this message only posted: 2 Jun 2017 13:43
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from:
Martin Wynne
West Of The Severn, United Kingdom



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p.s. Dave,

Having said all that, getting 5ft-6in out of 6ft-0in is pushing it a bit, and would mean an F-18 or F-20 turnout in 0-MF. Which is the longest normally found on the prototype for bullhead. Making a 1:20 vee from rail is no 5-minute task.

If you could ease the outer radius to 1870mm (6ft-1.6in), and set a generic (or curviform) V-crossing, you could do it at E-16 which is bit easier to build, and saves some space:





Martin.

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from:
Jim Guthrie
United Kingdom

 

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madscientist wrote: Now my space contraints mean my main line double track inner curve is at 6 ' ( sorry I'm an old money man ! ) And I need to diverge inside that to access the goods line , that divergence radius , I'd like to keep to a min of 5'6" 

I haven't temploted this yet.  But even in O-MF am I storing up issues here 
Dave,

I did almost exactly that formation for the trailing cross-over on Heyside for Richard Lambert - at the signalbox end of the layout - and it has worked very well with all his locomotives.   Heyside is laid to O-MF standards and the minimum radius throughout was supposed to be six feet but we had to break that rule to make this crossover.    I don't have the Templot file since the work was done on a laptop which no longer functions but I'll check with Richard Lambert to see if he still has the file around.

Jim.

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5th message | this message only posted: 2 Jun 2017 19:36
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from:
madscientist
 

 

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Thanks Martin , I had a feeling that the gauge O guild trackwork technical sheets had a whiff of male cow manure about it.

And thanks to the others for their additions and comments

I'll post the box file sometime this month for comment. The layout is a cut down version of Badmington aimed at WR stream diesel transistion period
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