Building a Wye

I want to build a Wye into a corner of my loft layout so that O can use it to turn 2 coupled SD locos or a small (SW1500 type) shunting loco
with a passenger (observation) car so that it can be turned to face in the opposite direction.
Trouble is there is very little space and it looks like I may have to go down to 18" radius curves to achieve this, although I'd prefer to keep the minimum to 24".
I know that I have to keep the 'end' leg of the Wye long enough to take to 2 locos so that is a given. I won't go in by way of a straight line so I realise it will have to be at an angle (around 45 degrees) from the corner of the loft, then I will have to make the curves tight to get in to the track that is already laid.
This picture http://mikehughes627.fotopic.net/p57723024.html shows the baseboard when it was newly constructed while this picture http://mikehughes627.fotopic.net/p66941259.html shows the same corner with the main tracks added in place.
Is there any simple system for working out where I need to put the switches (points) to enable me to lay the whole Wye or is it simply a case of trial and error.
I am using Peco code 83 track and I have 3 No 4 turnouts to minimise space taken up by turnout.
Your help and thoughts appreciated
--
Mike Hughes
A Taxi driver licensed for London and Brighton
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On Sat, 9 Oct 2010 12:42:25 +0100, Mike Hughes

Use set track curves and set track turnouts all handed the same way.
It's been many years since I did something like this, but ISTR it took three curves and three turnouts. I can't even remember which manufacturer , radius etc but it works because the curves and the turnouts have the same geometry.
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On 09/10/2010 07:42, Mike Hughes wrote: [...]

Yes, make several curve templates to cork roadbed width of the radius you think you need out of boxboard (use a nail and string), when you do this, also draw the centre-lines of the curves. Make templates of the turnouts you'll use, too, using actual turnouts to draw the edges of the ties and the centre-line along each leg. Mark the edges of the Turnout roadbed by measuring from the tie ends, and adding about 1/4" (6mm). Mark the the position of the throwbar and the frog. These will help locate the turnout. Also make a few straights.
Fiddle around with these templates until it looks right, sighting along them. When satisfied, pin in place, and draw along the edges. Also mark the centre-line by punching holes with a nail and using a pen pencil to mark spots. Draw the centrelines, and lay your cork, etc. When yoyu lay the track, place the turnouts _first_, then offer up the flex track, and cut slightly long. Pin temporarily, and adjsut length of flex track, etc.
If you like, you can incorporate easements (spiral) leading from straight to curve as well. You'll find these templates useful in future.
BTW, if you make a scissors wye, you will need less pace. Sketch it to see what I mean. Complication: a crossing, which may have to be curved on both legs to save space, thus entailing scratchbuilding.
An alternative is to make a boxboard template of the whole space, if you can find a large enough box to provide the template material. Advantage: you can do this wherever you have enough (temporary) space, such as the living room floor.... ;-)
HTH & have fun, wolf k.
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Would wye turnouts help? I know Peco make them. They reduce the space even more than #4s.
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The Peco No 4's are in fact Wye turnouts.
I'm up to my neck with work matters at the moment (annual taxi overhaul) then will be going to the NMRA BR conventions so it may be a couple of weeks before I get to try out the ideas I've been given.
Thanks for all suggestions I've received.
I'll post my results in due course.
--
Mike Hughes
A Taxi driver licensed for London and Brighton
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Mike Hughes wrote:

The quickest way is to get some actual turnnouts and 18" radius set-track and shuffle the parts on the kitchen table. A symetrical configuration with three wye turnouts linked at 120 degree angles by only curved tracks will give you the smallest possible arrangement, but given a corner location and presumably a larger radius 90 degree curve across the corner, then the other two curves, including turnouts, will be 45 degrees each. The tail might look better at a different angle than precisely disecting the 90 degrees of the baseboard corner. This is one of those situations where your personal opinion of the appearance probably won't precisely match the geometrically perfect track layout :-) The tail track can be a good spot for a small refueling oil tank on a stand, or a sanding facility or drivers tea room or ... For that reason you might want the tail track off-set by 50-60mm to provide space for the scenic details.
Greg.P. NZ
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