Transition at top and bottom of incline?

Any questions about designing a model railway layout or problems with track work.
abenn
Posts: 240
Joined: Thu Jun 05, 2008 11:03 am

Transition at top and bottom of incline?

Postby abenn » Wed Jan 28, 2015 12:14 pm

I'm planning my first N gauge layout, having run OO gauge for several years. I want to have an incline, leading to an overbridge, and wonder if there's any trick to making the transition at the bottom and top of the incline. Any tips or tricks please?

User avatar
Bufferstop
Posts: 12469
Joined: Thu Mar 11, 2010 12:06 pm
Location: Bottom end of N. Warks line

Re: Transition at top and bottom of incline?

Postby Bufferstop » Wed Jan 28, 2015 1:01 pm

I wouldn't say there's any tricks to it, needs to be a gradual taper at both ends. If you can form the top and bottom transitions by bending the board, you won't get a sharp edge marking the transition from incline to horizontal. This is definitely something that benefits from a dummy run. You need to test with the stock you are going to use, in particular rigid frame 0-6-0s or longer and bogie stock with long or six wheel bogies. Watch out for underfloor fuel tanks etc on long diesels.
Growing old, can't avoid it. Growing up, forget it!
My Layout, My Workbench Blog and My Opinions

abenn
Posts: 240
Joined: Thu Jun 05, 2008 11:03 am

Re: Transition at top and bottom of incline?

Postby abenn » Wed Jan 28, 2015 7:49 pm

I'll be using 6mm ply, so I guess that would give a gentle curve. I suspected the answer would be "try it and see", so I'll have to buy a couple of locos before I finalise my track -- I'm certainly going for a class 66 diesel, and probably a Pacific steamer for "heritage" days.

User avatar
Bufferstop
Posts: 12469
Joined: Thu Mar 11, 2010 12:06 pm
Location: Bottom end of N. Warks line

Re: Transition at top and bottom of incline?

Postby Bufferstop » Wed Jan 28, 2015 8:05 pm

If you cut the ply either side off the trackbed, then put a wedge under the free end it automatically forms the sort of transition you need. The top need a bit more thought as you need to put in a support at the right height to screw down the track bed.
Growing old, can't avoid it. Growing up, forget it!
My Layout, My Workbench Blog and My Opinions

User avatar
Emettman
Posts: 2275
Joined: Fri Jun 20, 2014 4:43 pm
Location: Cornwall UK
Contact:

Re: Transition at top and bottom of incline?

Postby Emettman » Wed Jan 28, 2015 8:22 pm

If there's lots of length available for the incline, this is no great problem.
As Bufferstop says, a trackbase fixed at the horizontal and curved gradually (up, down ) to match the incline helps avoid vertical jerks.
Partially cutting the track underneath may ease vertical flexibility.

If the space for the incline is limited, everything allowed for the transition will make the degree of the main incline worse.
(A foot of transition delivers near enough half the "rise" that a foot of main incline does)
I've not seen a formula or recommended tolerances for "sharpest acceptable transition" so this may take some experimenting with, especially if the main gradient is also bordering on an acceptable limit.
(minimum adequate clearance for the overbridge also helps, but may not be best cosmetically.)

Let's see. A set of numbers just plucked... A 60mm change in rail level at 1:50 would take 3 metres, not allowing for transitions.
If 150mm is allowed each end for the transition, that 300 mm would deliver 3mm of height change instead of 6mm. so the remaining 2.70 metres would have to deliver 57mm of height, instead of 54. That takes the main gradient to 1 in 47.3.

A definite effect. If the original planned gradient is steeper to start with, or the allowed transitions longer, then the steeping effect will be worse.


I suspect the longest wheelbase with six (or more) coupled driving wheels will be the most sensitive, or unforgiving.
And if the transition is on a curve, I'd make it twice a long as what I thought I could get away with on a straight.

Chris
"It's his madness that keeps him sane."

abenn
Posts: 240
Joined: Thu Jun 05, 2008 11:03 am

Re: Transition at top and bottom of incline?

Postby abenn » Wed Jan 28, 2015 9:41 pm

I'm planning on one track crossing over the main lines on a lattice girder bridge. To get scale headroom I need, I believe, 27mm from top of rail so, allowing for depth of the track and the bridge's girders, I think I need my incline to rise about 35mm. Does that sound about right?

Incidentally, is a 1:40 gradient generally acceptable? That's what we had on the real thing where I worked, and would give me a total length of about 2.3m allowing for 300mm transition at each end. I can achieve that in a straight section behind the scenes.

b308
Posts: 5006
Joined: Sat Apr 15, 2006 5:48 pm
Location: North Worcs

Re: Transition at top and bottom of incline?

Postby b308 » Thu Jan 29, 2015 10:14 am

1:40 is fine!

Re the transition, before you finalize the build check your stock over it as the tops and bottoms of gradients are one of the best uncoupling ramps you can design!

User avatar
Emettman
Posts: 2275
Joined: Fri Jun 20, 2014 4:43 pm
Location: Cornwall UK
Contact:

Re: Transition at top and bottom of incline?

Postby Emettman » Thu Jan 29, 2015 3:03 pm

abenn wrote:I'm planning on one track crossing over the main lines on a lattice girder bridge. To get scale headroom I need, I believe, 27mm from top of rail so, allowing for depth of the track and the bridge's girders, I think I need my incline to rise about 35mm. Does that sound about right?

Incidentally, is a 1:40 gradient generally acceptable? That's what we had on the real thing where I worked, and would give me a total length of about 2.3m allowing for 300mm transition at each end. I can achieve that in a straight section behind the scenes.


35mm rise seems reasonable. At 1:40 a sharp edged incline would be 1.4 metres. Add 600mm to compensate for the loss of height gain in the 300 transition, I get 2 metres as the rough calculation requirement.

1:40 is a challenging but not impossible gradient, depending on the length of trains to be run.

I remember the snippet (just confirmed):
"All Up SR trains required to be banked on this curving half-mile of 1-in-36" between Exeter St Davids and Exeter Central.

And of course "The Lickey Incline, south of Birmingham, is the steepest sustained main-line railway incline in Great Britain. The climb is a gradient of 1-in-37.7 (2.65%) for a continuous distance of two miles "

Branch and industrial lines could do appreciably worse, but 1:40 is a hefty mainline haul. ( for 2m, about 1/10th of a Lickey)
"It's his madness that keeps him sane."

abenn
Posts: 240
Joined: Thu Jun 05, 2008 11:03 am

Re: Transition at top and bottom of incline?

Postby abenn » Thu Jan 29, 2015 7:33 pm

Thanks. Once I get my layout design more developed I'm sure I'll be able to find more length the fit the inclines in (one up, one down), so should be able to do better than 1:40.

User avatar
Emettman
Posts: 2275
Joined: Fri Jun 20, 2014 4:43 pm
Location: Cornwall UK
Contact:

Re: Transition at top and bottom of incline?

Postby Emettman » Thu Jan 29, 2015 8:31 pm

abenn wrote:Thanks. Once I get my layout design more developed I'm sure I'll be able to find more length the fit the inclines in (one up, one down), so should be able to do better than 1:40.



This may be saying the obvious, but one of the best ways to ease gradients is if *both* lines approaching a bridge have them, the lower track having *dropped* a bit to help with clearance.

This might mean cutting a depressed trackbed in the baseboard, or taking the lowest point on the layout (underneath the bridge) as zero height, leaving the main "flat" area at say +12mm. The rising incline as before would only have 25mm to make, instead of 37.
That comes with some advantages in return for the extra work: room for the flow of scenery below track level elsewhere on the layout, and a nice thickness to take (hidden) wires *above* the board, if wished.

Chris.
"It's his madness that keeps him sane."

abenn
Posts: 240
Joined: Thu Jun 05, 2008 11:03 am

Re: Transition at top and bottom of incline?

Postby abenn » Fri Jan 30, 2015 8:12 pm

Thanks Emettman, but I think I'd rather keep things simple by only taking the inclines up above the board. As I said, I now think I've got plenty of space to do it :)

User avatar
Emettman
Posts: 2275
Joined: Fri Jun 20, 2014 4:43 pm
Location: Cornwall UK
Contact:

Re: Transition at top and bottom of incline?

Postby Emettman » Fri Jan 30, 2015 9:37 pm

abenn wrote:Thanks Emettman, but I think I'd rather keep things simple by only taking the inclines up above the board. As I said, I now think I've got plenty of space to do it :)


That is of course quite correct, given that immense and rare luxury of space!

Chris.
"It's his madness that keeps him sane."

bodger
Posts: 7
Joined: Thu Feb 26, 2015 10:48 am

Re: Transition at top and bottom of incline?

Postby bodger » Thu Mar 05, 2015 2:56 pm

If you're using a strip of, say, plywood as the base for the inclined track perhaps it would help bending if you scored it transversely - the underside at the bottom of the incline, the upper side at the top. It's reminiscent of the scored MDF that you can buy and use to make curved scenic back boards.

User avatar
RAF96
Posts: 694
Joined: Tue Feb 19, 2008 1:39 pm
Location: Dereham, Norfolk, UK

Re: Transition at top and bottom of incline?

Postby RAF96 » Sun Mar 08, 2015 10:56 am

it would help bending if you scored it transversely - the underside at the bottom of the incline, the upper side at the top. It's reminiscent of the scored MDF that you can buy and use to make curved scenic back boards.


Kerfing
RAF Halton Brat - 96th Entry
http://www.halton96th.org.uk/robs_rails.html
β-tester


Return to “Track/Layout Design”

Who is online

Users browsing this forum: No registered users and 3 guests