Gradient for 00 layout

A 4% gradient would give you a length of 2m, which sounds about right.

A 70mm rise will clear all OO stock. A 1:25 climb is a bit steep and only very short trains will manage it. I use a 1:40 which needs 3M run but even then had to convert the rising track to steel in order to prevent slipping no matter what type of traction was involved. The curves will be tighter too - I have problems with 1M radius and you will have to manage on half of that - this causes some extra drag and acts like an even steeper hill. I had designed a diagonal crossing system which involved one track rising and the other descending which cuts the distance involved in half. I didn't use it because my baseboards are too thick but if it is designed in at the outset then it can be quite characteristic of several urban prototypes.

Peter A

Early on I read somewhere that a max gradient of !:30 was acceptable for OO, I have since found this a bit steep and given when it was written that may be a max for shorter trains (I play with N so tend to have quite a few axles to haul).

Regards

Mike

80mm seems a bit high to clear an 00 gauge track. I also planned an overbridge so did some load tests on a 1:30 gradient to clear 2.5 ins so the length of the incline was 6ft or there abouts. Some of the locos managed 5 coaches and some were a dismal failure. With a bit of redesign I think I can manage the incline over 7 to 8 feet.

Kevin

I've just been through an exercise to build an incline and I kept mine to 8 cm difference in a 2% incline (1:50) or thereabouts.

It's on a curve so this has an effect as well.

I did try a slightly steeper incline at one point only to be hit with slipping locos and lifting wheels so I was forced to rebuild it at the lower level.

Cough cough - please note that my woodworking skills leave a lot to be desired - cough cough.

-- Rod

This is cutting it a bit fine, and assumes selective compression. You can do some selective compression, but there is a limit to how thin a bridge floor looks OK. Making the girders shallower than they should be if modelled accurately will help the illusion of an adequate bridge.

Note that the rise at the rail rise must allow for:

-- the depth of the girders supporting the track, which tie the main bridge girders together and transfer the load; on typical through spans, this will 2ft (8mm) or more

-- the depth of the sleepers, which are thicker on a bridge; or the depth of the ballast below the rail; allow 1 to 2ft (4 to 8mm)

-- the height of the rail itself (2 to 3mm)

-- the minimum clearance above the rails of the lower track. This is

15ft (60mm) or more.

So we get 60 + 2 + 4 + 8, or 74mm minimum rise at the rail: round it up to 75mm, and use that as your minimum.

[snip excellent points on the effect of grade on traction]

One small but not insignificant addendum: allow at least an additional foot at each end of the gradient for the vertical curve. Too sharp a vertical curve will result in coupler and tracking problems.

Thus, a 1:40 (2.5%) grade requires 3000mm (10ft) for a 75mm rise, plus another 600mm (2ft) for the vertical curves, or 3600mm (12ft) in all.

HTH