Building a "rolling road" test track in 7.25" gauge

[Benjamin Maggi]

I am building a 7.25" gauge, 3.75" scale, "Sweet William" Welsh tank locomotive (0-4-0). I would like to build an inexpensive roller-bearing set up to set the engine on for when I break it in on compressed air, or perform maintenance, etc. Right now we just support the two ends on wood blocks but something a bit better would be nice. Simple and cheap are important. Easily portable would be nice too.

The chassis only weighs about 100 pounds so it don't have to be built like crazy.

Any ideas or pictures? Thanks.

[Dick_Morris]

This is what I did.

https://www.chaski.org/homemachinist/vi ... 74#p425874

[Steve Goodbody]

Hi Benjamin,

As luck would have it I last weekend finished and tested the rolling road for my 7.25” narrow-gauge Hunslet, a similar size to your loco.

I’d been mentally working through the design for the past few months and, with the help of a few basic sketches, built the road over the last couple of weekends and tested it last Sunday with the loco running on air – all went well.

One of my goals was to arrive at something that I can use single-handedly without any heavy lifting – the loco weighs around 700lbs so that’s an essential requirement. I achieved this by mounting the road to a small hydraulic lift cart (Harbor Freight) so I can roll the engine straight onto the road from its building stand. Taking things carefully, I find I can get the engine safely on/off the cart in about 5 minutes each way. As an aside, I additionally want to use the setup as the means to transport the loco from my workshop to my trailer for transportation and so wanted this to be easy to use.

I haven’t yet taken any pictures, but will follow up with some (and the roller bearing details) in a later post. Here’s a brief summary in the meantime:

The road consists of two 1.5” x 1/8” steel square section tubes set on 2x4 lumber ties, the tubes are spaced 7.25” apart to form rails to lead the loco to the roller bearings. The roller bearings are 1” diameter cantilevered bearings mounted to the inside surface of the square tubes - the tube is locally cut away for the rollers - such that the bearings are also at 7.25” gauge. The top of each roller bearing is 1/32” below the top of the rails, and each wheel settles between two roller bearings set 1” either side of the wheel center-line. As a result, the loco’s wheels end up about 1/8” below rail height when sitting between the bearings, this means that gravity prevents it from going anywhere when it’s running. I use a small hand-winch to pull the loco back up to rail-height when finished, there’s no way I can move it otherwise.

The result wasn't expensive at all - my loco (like yours) has a very short wheelbase and so the rolling road is only about 30 inches long in total. The material cost was minimal.

As I say, I’ll follow up with a few pictures to help visualize the above.
Best regards
Steve

[Bill Shields]

Roller blade bearings...very cheap and rugged

[Steve Goodbody]

Here are some pictures taken this evening Benjamin, hope these are of some help.

The bearings are needle roller cam followers, Smith part number CR-1-XB, rated at approximately 3000 lb radial load each. Excluding the lift cart (which has other uses and so is more a tool than material), the bearings were by far the most expensive part of the setup at approximately $17 each. However, since they're taking the full weight of the loco and are pretty vital, I'd rather spend the money for those. The total cost excluding the cart was around $150.

Some more pictures to follow.

Best regards
Steve

[Steve Goodbody]

[Steve Goodbody]

Here's the last set of pictures.

Best regards,
Steve

[Benjamin Maggi]

Thanks Steve. That is exactly what I am thinking of (minus the cart part). Your pictures were very helpful.

By the way, that is a great looking engine of yours! I don't know where you are located, but I would love to see it sometime. Assuming that the 7.25" gauge of your engine doesn't imply Europe, you must be in the North east too.

[Benjamin Maggi]

If my wheels are 6.625" diameter on the tread, with a wheelbase of 13.3125", how far apart should the rollers be if I mount them so that their bearing surface is 1/32" below the running surface of the tubing? I know it should be an easy math problem, but math for me is never easy!

[Steve Goodbody]

Hi Benjamin,

The short answer is, for a 1/32” drop and assuming 1” diameter rollers, they would only need to be spaced apart by approximately 1” total and hence would be so close together that they would be butting up against each other. Recall that I set my rollers so that their tops are already 1/32” below the rail height, and I then set them apart far enough apart to add another approximately 3/32” of drop in addition, bringing the total drop to about 1/8”.

The math problem is laid out in the picture below, and I've summarized the solution for 3/32” wheel drop between the rollers (based on 1” diameter rollers and your 6 5/8” wheels):

For 3/32” drop:

Angle A = 13.66 degrees
Distance N = 0.78 inches
Distance M = 0.11 inches
Distance D = 0.89 inches

Hence the spacing between the rollers, 2 x D, would be 1.78 inches to give a 3/32” drop.

Best to check my math, the easiest way would be to draw out some circles to scale and see if the theory works in practice!

Best regards
Steve

[Benjamin Maggi]

Thanks. It sounds pretty good. I suppose it isn't all that critical. If I can machine a cylinder, I should be able to machine this.

[Steve Goodbody]

Benjamin - sorry, I forgot to answer your other questions.

I'm in NJ and a member of the NJ Live Steamers, but only an occasional visitor to the club unfortunately. I'm hoping to steam the loco on the rolling road sometime over the next couple of weekends in order to see what needs sorting out when it's hot - there's always something. Hopefully I'll build a few driving/passenger cars over the winter and be ready to visit the NJLS track with the loco next spring. Search on "A Long Term Project" for more info on the loco.

Good luck with your loco and rolling road - hopefully we'll be able to meet face-to-face before too long.
Best regards
Steve