Union Pacific Big Boy in 3/4 Inch Scale

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Carrdo
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Union Pacific Big Boy in 3/4 Inch Scale

Post by Carrdo » Thu May 04, 2006 8:58 pm

Want something different - a little bit more complicated? Try this in 3/4 inch scale.

We would never ever have contemplated such a locomotive if the original builder had not done most of the work. Unfortunately, he passed away before the model could run on steam.

Our aim is to finish it as a true working locomotive. And, as you know, to make a practical machine of this type in this scale, is more difficult than building in a larger gauge.

Externally, we will try and keep the extraordinary detail of the original builder but where practicality and scale clash, it is being modified to make it a working model. For example, the articulation on the front engine has to be greater than on the prototype for it to be able to run on tighter and rougher model track. To date, the locomotive will now easily negotiate a 25 foot radius reverse curve when running forward and most of the time when running backwards. With a few additional modifications, we will achieve engine and tender stability in both directions. The caterpiller tender has proven to be a challenge in certain situations as sometimes it wants to climb the rails running backwards when the long rigid wheel base is leading.

The boiler was originally designed to run on coal but we plan to run it on propane. It is superheated.

There are only two castings used in the entire model, the cylinders and the drivers. The cylinders for both engines are from the Coventry Pacific, as supplied by Miniature Power Products, and the drivers are from Martin Evans Columbia available from Blackgates. The 3/4" scale drawings came from True to Scale Services out of England which produced them a number of years ago.

By the way, the Union Pacific Historical Society can supply a CD containing all of the full size engineering drawings for the Big Boy. All 2900 of them!

When we purchased it about a year ago, the price was $30 plus $5 for shipping and handling. At that price, it is a very good deal.
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Carrdo
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Post by Carrdo » Thu May 04, 2006 10:26 pm

Some additional photos.
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Carrdo
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Post by Carrdo » Thu May 04, 2006 10:33 pm

Some additional photos 2.
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Carrdo
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Post by Carrdo » Thu May 04, 2006 10:41 pm

My hat is off to the original builder. Entirely made by one man.

This was not his only locomotive.
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locodan5416

Post by locodan5416 » Fri May 05, 2006 12:21 am

I like it, just curious though, how long is that centepede behind the engine? Do you run it? Do you use extension rods for the throttle and reverser?

Dan

by the way, I like the wheels, I'm definetly going with the Blackgate Wheels for my Columbia now... What is the big event going on in England right now? I called Blackgates, no response, said they'll be back Monday

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Jim_Nolan
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Post by Jim_Nolan » Fri May 05, 2006 1:10 am

This weekend is the Northern model engineering show at Harrogate. It attracts most of the major suppliers in the hobby; I will be there Sunday with my shopping list.

On topic for a bit, what a cracking piece of work, I am always envious of the level of detail some modellers can archive in the smaller scales.

Jim

Guest

Post by Guest » Fri May 05, 2006 10:00 am

Don & I are in on this project together so he & I will both try to answer some of your questions. Don is the one who has been posting to this site, so I'm far from being an expert on this.

First, as we got it, the locomotive was only about 80% complete so it is a long way from being a running proposition. Gerhardt, the builder, lived in Sarnia & he started building a President series Pacific after he retired from Chrysler. He finished the Pacific about 1994 and started on the Big Boy about a year later. According to Gerhardt's son Gunther, when he was building the Big Boy, his father would go down to the shop about 8:30 in the morning and quit about 9:00 (or later) at night, with breaks for meals & housework in between (10 to 11 hour days). He kept this up for 5 years!

There is an incredible amount of very fine work in the model and I think we were very lucky to acquire it. The engine is 63 inches long, the tender is 33 inches long and when you add all the parts together the present engine weight is 245 pounds, while the tender weighs 68 pounds. The wheels and the cylinders are the only castings in the model.

Since we picked up the model last September, we have been learning how it is built and making modifications so that it will hold the track the way that it should. At the beginning, the tender would derail even on straight track. Now it will go around corners quite well and works well on both the Hamilton & Milton tracks.

Basically, the changes consisted of putting a ten degree taper on the wheel flanges, freeing up the axleboxes so that they could slide easily and tip (most important), and increasing the end float on the axles in the caterpillar section of the tender. The springing was also too stiff on both the engine & tender. Wheel flanges are "scale" so the flange taper has to be greater than usual. Springing and suspension have to be flexible so that the wheels can follow the track, no matter what it does. For this reason I also added a spring on the truck kingpins on both the lead engine and tender. Unfortunately, axlebox travel is also "scale" so that limits the ability of the model to handle really poor tracks. In addition, there are needle bearings in all the main axles on both engines, the big ends of the connecting rods and in the trailing truck axles.

The boiler is copper with a combustion chamber & it has several leaks which we will tackle later. I'm sure that Gerhardt intended to fire it with propane; if you study the pictures, you will see that cleaning the tubes would be next to impossible and reaching over that tender would not be the easiest thing to do. The present plan is to run permanent piping under the tender for propane with the controls at the back of the tender. These would probably be removable as would also be any extension handles necessary to operate the cab controls.

I hope this answers some of the questions & I'm sure there will be more. If we're lucky it might be ready to run under steam sometime next year.

Richard Trounce

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willjordan
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Post by willjordan » Fri May 05, 2006 10:26 am

I had a friend with a centipede tender in 1.5" scale and keeping it on the track was a problem until we loaded it. With enough weight on the rear of the tender, it tracked well without problems. Light, it would follow mainline track in forward, but yards and backing were impossible. 200-300 pounds of weight improved its tracking markedly.

We need to remember that our scaling is linear while weight increases as the cube, so spring rigging and such need to be lightened up a great deal or ballast needs to increased to get proper handling. This shows up most clearly in issues like the centipede tender and pilot wheels. The forces don't scale linearly, so special compensation needs to be made in approriate areas.
grace & peace
will

[url=http://willjordan.com]Will's Web Pages[/url]

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Andypullen
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Post by Andypullen » Fri May 05, 2006 10:34 am

Hi Don,

WOW! That'll go well with John Hudak's Challenger. You'll have to get them together.

Andy Pullen
Clausing 10x24, Sheldon 12" shaper, ProtoTrak AGE-2 control cnc on a BP clone, Reed Prentice 14" x 30"

Guest

Post by Guest » Fri May 05, 2006 10:59 am

Yes, As Will says, on the Big Boy, weight is an issue. With a 10 pound weight in the coal space in the tender, it tracks well, without it, not nearly so good. The tender will probably hold about a gallon of water, but that will only add 10 pounds to the tender weight.

Even at 245 pounds, the locomotive would also benefit with more weight. For both engine & tender, there are just too many wheels for the weight of the model, so when you do the math, each axle only sees 20 pounds or less. If you look at many of the smaller models; Atlantic, etc., the axle weight is greater & because most of them have been designed & built as models, vertical axle travel is greater & the flanges are bigger. All of these help to make for a locomotive that holds the track well.

One of the many things to figure out is how to add more weight to both the engine & tender without it showing. We'll do the best we can.

Richard Trounce

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JohnHudak
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Post by JohnHudak » Fri May 05, 2006 11:19 am

Andy, It would be quite a sight to see both the BigBoy and Challenger together. But at this point the BigBoy seems to be about 3 or 4 years ahead of me....And as you know, now that May has arrived, I'm back to work on the Tanker. I did however get the main rods finished for the rear engine, which is what I wanted to do. Richard and Don have been sending me up-dates on the BigBoy progress, and I'm trying to convince the wife that we need to head up to Toronto this summer, as I've got to see this thing in person......John

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Carrdo
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Post by Carrdo » Fri May 05, 2006 11:58 am

If anyone is interested, some of the locomotive's working components were taken from Roy Johnston's Timken "Four Aces" locomotive.

A series of articles by T Parkinson on Roy's locomotive ran in Modeltec starting in late 1984 or early in 1985. For example, the poppet valve throttle/superheater header assembly is a copy of the Four Aces design.

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