“Some use HOn3 track for On18 – I did. If you run the numbers, that 9 mm (0.354 in) gauge track actually comes out to a 17 in (792 mm). Since there was a real world 18 in gauge track we simply call this On18 .. rather than On17.

On18 Car Width and height

In order to ‘Fabricate’ an On18 clearance gauge we need to attempt to find the width of a car/engine.

I found a thread on Trainorders.com where it goes:

Q: What is the width of a narrow gauge passenger car, and what is the width of a standard gauge passenger car?
A: A standard gauge (56 1/2″) car is 10′ 0″, 2.12 times gauge.
Colorado narrow gauge (36″) cars ran about 8′ 6″, 2.83 times gauge, while Milwaukee Roads narrow gauge equipment ran closer to 8′ 3″.
Maine 2′ gauge cars were very narrow, about 6′ 5″, but that is 3.2 times gauge!

Fig 1

That gave me enough information then to calculate the width of the car for On18 .. (Pseudo-Engineering again). If I keep the same proportion to the gauge that the Maine 2′ used .. then …

3.2 x 18 = 57.6″ or 4’9.6″ .. which I rounded up to 58″/4’10″. In O scale that is 1.2″

Fig 1 shows a 2ft gauge locomotive that I re-sized for 18″ gauge. Note that I came within a inch of the calculated width (yes .. dimensions are only ‘sorta kinda’ correct .. but so is this entire guesstamation I am conducting.

Fig 2

All well and good. No – we humans don’t resize (other than expanding over time) so let’s keep the vertical dimension for the loco/car height from the 24″ loco of 85.4″ and apply that to our 18″ loco. This is where I am not sure of –

we need to know the distance from the top of the rail to the bottom of the car
Would be helpful to KOWW this!!x
to which we can add our 85.4″ (1.78″ O scale).

I see some use HOn3 trucks and so looking at the NMRA RP-23 Bolsters page I see that the “Center Bolster Bearing Above Top of Rail” is 1/4″. Elsewhere I find that Floor Height for HOn30 is 7.2 mm (0.283″).

So .. until told different
If these numbers are wrong, then show me my errorx
I am going to go with … 0.283″ (13.6″) + 1.78″ (85.4″) = 2.063″ (99″) from top of rail to top of car, and 1.2″ for the car width.

Fig 2 then is a starting point with width, height to floor and height to roof (Version 2). On the right (Version 1) is the one I made up several years ago. I just noticed while updating this that .. yes .. I had the gauge wrong. *sigh*

Thoughts ..

  • Dimension E shows as 0.317″ on V1 gauge. I can’t remember where I got that but seems it should be to bottom of floor – 0.283″ V2 gauge. This should be the dimension to the face of the truck.

Dimensions P & E

Dimension E is 0.283″ – or – 0.317 – or – something else. Dimension P I *derived* from an On18 truck I am working on which measures 18.7 mm across the journals .. so I rounded up to 20 mm and split the diff for a 10 mm / 0.394″ P dimension.

If we agreed on the current dimensions this could be called something like Gauge A – minimum dimensions
If these dimensions are not correct then please point me in the right directionx

If we waned to add a slanted/clerestory roof  it would really add little weight and would make sense for humans to occupy. I did this with V1 of the gauge.

On18 Gauge Version II (HOn30 trucks)

For now I am calling this good to go unless feedback convinces me otherwise.

Note that this is made for those using HOn30 trucks. I am making another version to use my own On18 truck.

Next step is to print one and share the STL file.

On18 Gauge Version II (On18 trucks)

This is designed to use my own On18 trucks with 20″ wheels

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Thomas Heath Trollope

I am on the same page. I have been loosely using 20 and 24 in gauge as a guide. I deduced that the car width of roughly 3X gauge (was also backed by Mr. Fairlie) and came up with 5 scale feet for width and a similar 2 foot car height. The cab floor of the 24 in gauge Decauville 3 ton 0-4-0 also has a 24 in height.