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topic: 783Increased Clearance around curves
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posted: 7 Apr 2009 14:40

from:

Andy G
 
 

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Martin,
This is probably going to fall into the mathematically difficult/impossible camp.  The issue is a curve going round 90 degrees.  At either end the track is straight and therefore has a track spacing of 44.67mm (P4), however, going round the bend (this has been driving me that way!) it needs to have a spacing of 54mm (for instance).  I've managed to do it through various tricks and trial and error, however, it would save a lot of hassle if Templot was able to do it.

I quite appreciate that this could be impossible!

Andy

posted: 7 Apr 2009 15:39

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Andy G wrote:
This is probably going to fall into the mathematically difficult/impossible camp. The issue is a curve going round 90 degrees. At either end the track is straight and therefore has a track spacing of 44.67mm (P4), however, going round the bend (this has been driving me that way!) it needs to have a spacing of 54mm (for instance).
Hi Andy,

That's what the slewing functions are for. :)

Put the peg on the 45-degree mid-point of the outer template(s) - geometry > peg positions > peg on mid-length menu item. Make split at peg. Put the peg at the outer end. Apply a slew to each new half template, setting the slew amount to the increase in spacing needed, say 8mm (may be negative) -- geometry > slew (nudge) > slew using mode 2 menu item, then geometry > slew (nudge) > change slewing zone length > match length to template menu item.

For something similar see: message 3990

Your case is a lot easier, because you are not looking for concentricity at the mid-point. Just slew each half outwards as required by the same amount. Then a slight F4 adjustment to fill the gap (for a perfect result you should really adjust both templates to the mid-point of the gap).

You could instead slew the inner road, or slew both by half the amount. But it's generally better to leave the tighter radius undisturbed and modify only the easier one.

I could do a bit of Jing video?

A 90-degree curve between straights has a bit of a train-set look to it. At the very least you need some transitions, and ideally not exactly 90 degrees. :)

regards,

Martin.

posted: 7 Apr 2009 16:09

from:

Andy G
 
 

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Hi Martin,
I'll give that a try.  To be honest the example I gave was simplified to avoid confusion, we are using transitions though at one end of the layout the track does bend through 90 degrees over a distance of about five feet - compromise of building a roundy round in a limited space, and this is the end Jim Summers keeps using a photo of!  Photos of the layout are here, Slattocks Junction.  All of the front track has to be replaced as it has proved impossible to paint the sleepers and whilst the goods yard was drawn on Templot the mainline predates the use of it.  We are therefore taking the opportunity to redraw it and hopefully getter better alignments and flows.

posted: 7 Apr 2009 17:23

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Andy G wrote:
To be honest the example I gave was simplified to avoid confusion, we are using transitions
Hi Andy,

Ok, if you use transition curves you can create the track separation quite easily using transitions only.

Set up the straight double track at 6ft way and some curved double track at say 8ft way or whatever. Then use the make transition function to link them, separately for each track. Here's what I mean, with the amount of widening exaggerated for clarity:

trans_widen.pngtrans_widen.png

trans_widen_spacing.pngtrans_widen_spacing.png

You will find the outer transition zone is much shorter than the inner, and approximately centred within it. For large increases in spacing this method falls down, as either the outer transition length reduces to zero, or the inner transition becomes excessively long. You then need to apply slews instead, as explained before.

regards,

Martin.

posted: 7 Apr 2009 17:48

from:

Andy G
 
 

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I think that is how I've done it.  Doing it automatically would be nice but at least I know I approached it in the right way.

Cheers
Andy

posted: 7 Apr 2009 18:29

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Templot User
 
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----- from Andrew Jukes -----

Andy

If all else fails, you could use Scalefour Digest 21.1, page 17. Basically, you make s (the transition curve offset) for the inner track greater than the offset for the outer track by the increased track spacing you require. That also has the effect of increasing the length of the transition for the inner track.

Andrew Jukes



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