My current layout consists of two large loops with one at 'ground' level and the other approx 7 inches above it.  I want to connect the two loops using a helix that I will build by breaking through the wall into the furnace room.  Look at the pic attached that shows the levels of the tracks but note the 'break through' will be behind the breaker.

What grade can I safely use for this creation?  I was targeting 2% but run some long coal trains that pull 10-12 die cast K-Line hoppers and want to be sure my MTH locos will handle the load.

I calculate that grade (2%) as needing 350 inches of track to work  for 7 inches so almost 30 feet.

If I do a helix with two loops each would be 15 feet in circumference for a diameter of 5 feet.  Is my math right?

What radius would that yield as I have O54 now to allow everything to run smoothly?

Any other suggestions/advice besides forgetting the whole idea and just running two separate loops.



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Original Post

Let's walk through this. The formula for determining the circumference of a circle is 2X pi X radius or pi X diameter where pi is 3.1416.

A 2% grade is about 1/4 inch per foot so 350 inches of run is correct.  

So if we divide 350 inches by pi (3.1416), you get 111.4 inches or 9.28 feet. That's for one turn on the helix. To get 2 turns obviously divide by 2 and get 55 inches. Your math is correct .

The situation might arise when you are actually building the helix as you might not have enough room between the turns.  You also need to account for the baseboard that the tracks will sit on.  Also you will need access space for the "0-5-0" wrecker in case of a derailment . 

I built a layout long ago with a 78 inch diameter helix  that climbed 21 inches . It took 3 turns with a spacing of 7 inch per turn but there was only 5 inches of space between the rail top and the bottom of the baseboard. 

Good luck with your build. 


 Bill T.

There's no scale but O scale

CEO Overbeider Iron and Steel Company,  Crapton Works

By the looks of your picture you are using gargraves or Ross track over cork roadbed. The track is 1/2 inch high and another 1/4 inch for the cork. Allowing 1/2 inch minimum for the baseboard and at least 4 &1/2 inches for the train, you're at 5 &3/4 inches, not counting any kind of support for the base and air space for access. 

You won't be able to get 2 turns of O-54 track into the space allotted. You can only get 1 turn no matter what radius.  Try for a larger radius if you want a 2% grade  or stay with O-54 and increase the grade to 4% or more . 

Hope this helps. 

 Bill T.

There's no scale but O scale

CEO Overbeider Iron and Steel Company,  Crapton Works

There is a minimum rise that must be considered.  One has to take in account the thickness of the supporting structure plus the roadbed (if any) plus the height of the track track plus the minimum clearance of the equipment.  this will be about 7 inches or 1/2" for supporting structure plus 1/2" for track plus 6" clearance.

If you want a 2% grade, you divide 7" by 0.02 or 350".  The diameter iis 350" divided by π (3.14) or 112".

The only way to reduce the diameter is to increase the grade. A 4% grade yields a diameter of roughly 56".

If you can insert a few straight section of track into your helix making it more like an oval you reduce the circumference by the total length of straight.


it is really length that you are looking for - or run as in Rise/Run= slope

Here is a 7' x 5' space that gets it up and down - you need a reversing loop on each level - this is 169 inches of track for 4.2% slope rising 7 inches. Then, you could traverse both levels on stay on one level.

This all Gargraves wood tie

The wall tunnel would be just after the divergence of the turn-out - one switch on each level - this is a 4.2% slope - not out of hand

Adding length at 9 and 3 o'clock would push it away from the wall on the other side and reduce the slope.


Arctic Railroad


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I personally wouldn't advise a grade of 4.2%.  I think 2% or even 2.5% is ok, but any steeper and you're asking for trouble.

Your math is mostly right, but there's one thing you didn't think of (and I don't believe any of the others who responded pointed this out)...

If the two loops of the helix are STACKED, i.e., on top of one another, or even cross over one another, then they will probably have to have a minimum vertical separation of at least 5 1/2" for the train to pass under the next level of the helix!  So for practical purposes, you would have to gain all 7" in just ONE loop.  To keep the grade manageable, that loop would have to be about 9' across.  That's a floor area of at least 9 x 9 feet.  You didn't share the size or any details of your furnace room.

Luckily there's another option.  Using your current minimum diameter of O54, check out this crude sketch of what I called a "whale tail" :

Whale tail rotated

It gains length by folding back on itself.  I think you can get your 350" of run in a smaller 6 x 10 footprint.  Note, those reverse curves are going to add a lot of drag.  Personally I'm not a fan of die-cast cars.  If your trains aren't made up carefully with all heavy cars at the front, you might experience stringlining.  (Don't feel bad, the wrecks at Pennsylvania's Horseshoe Curve this year prove that it happens on real railroads too!)  That's one of the reasons I don't advise going steeper than 2.5%.

Sorry for the crude sketch.  And I welcome any additional feedback or criticism that would help Mr. JPS get what he needs.

Creep, coast, and pull.  We're not talking about cold fusion here.


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The area needed to be expanded to 7' x 6' behind the wall - now there is an up and a down ramp - no need to change the main table for a reverse loop

The slopes are 3.9% and 3.6% for the outer loop.

It is hard to see the main level switch under the 7" height switches in the track plan - the straights are custom cut and  4 cut curves are needed.

Again, all GG wood tie track used.

if you want the SCARM file, just email me.


Arctic Railroad


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