Steam & Excursion > N&W 2156

I made a quick road trip to the Museum of Transportation in St Louis today to see if N&W Y6a 2156 was still there (it is) and to photograph it before the trip east to Roanoke. I had originally planned to link up with a bud for lunch, but the schedule didn't allow ... I wanted to get out of town before traffic hit! I haven't visited the museum in over 10 years and WOW was I impressed by all the changes that have taken place (more on that later). 2156 looks like it is ready to go; the museum staff didn't have any idea as to when the move is going to take place, but the tool car that is supposed to accompany the move east is nowhere to be seen, so who knows.

Regards,
Burlington John



Edited 1 time(s). Last edit at 10/29/14 05:16 by burlingtonjohn.

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When we were in Chattanooga we went to the TVRM shop Sunday evening and that tool car was sitting inside the shop. They said it was supposed to be going to St. Louis but they didn't know when.

John

Why do they cut the rods on the wheels? I honestly don't know the answer--is it a mechanical reason, or just to make sure the engine never runs again?

From the looks of it they carefully removed the main rods. It's easier to take them off and put them on than it is to lubricate the pistons for no reason over a couple thousand miles.

Pump

Steam locomotives are basic machines; lubrication is critical given the large moving parts. A "working" steam engine is different than a "dead in tow" locomotive. The Big Boy at the Texas museum, for example, has piston rods which were torch cut, eliminating any risk of the pistons and/or rods seizing but also rendering it forever a non-functional locomotive. In the transition from steam to diesel it was common for rods to be torch cut as an expedient in moving locomotives never intended to be operated again.

Labiche Wrote:
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The Big Boy at the Texas
> museum, for example, has piston rods which were
> torch cut, eliminating any risk of the pistons
> and/or rods seizing but also rendering it forever
> a non-functional locomotive.


Eh, I don't know about "forever".... Anything can be made for the right price.

But yes, for towing a dead steam locomotive certain items must be removed before towing.

These days, it is extremely rare to torch something. Most items are carefully removed.

Cutting the piston rods doesn't render an engine non operating forever.
Frisco had cut 1522's piston rods before donating her to the Museum of Transportation. When we restored her, the City of Rolla, MO was kind enough to let us harvest the pistons out of 1501 which has been on display there since 1955. Her job as an organ donor made our engine operable.

Don't see anything "cut" in the photo.

Looks like the wrist pins, main rods, and eccentric rods
were removed properly and everything secured properly for
movement.

Yep, looks like they did it the way you do it if you're not pulling pistons, then you don't need to run lubricators either. Ready for the low speed move. Roller bearings on all axels, right? I'm curious how much prep work it took, has it been moved any distance recently?

Cheers, Dave

Piston rods on modern steam power are a hollow-bored, heat-treated steel forging. The material and heat-treatment specs are known. Same situation for steam locomotive driving wheel axles. Neither are not exorbitantly expensive to have custom-made. For 4-6-2 S.P. 2472, we had a new driving wheel axle forged from the correct type of steel, hollow-bored, heat-treated, and rough-machined. It cost a couple of thousand dollars.

So cutting the piston rods doesn't make a steam locomotive economically non-restorable. It's a small expense compared to the rest of the job.

- Doug Debs

What is the purpose or advantage of having piston rods or axles "hollow bored"?

Jim Montague
IRVINE, CA
Train and Nature photo Art

3751_loony Wrote:
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> What is the purpose or advantage of having piston
> rods or axles "hollow bored"?


Increased strength.

3751_loony Wrote:
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> What is the purpose or advantage of having piston
> rods or axles "hollow bored"?


In engineering terms, a piston rod is an example of a 'circular beam.' Beams can be subject to deflection (bending), torsion (twisting), tension and compression.

The material farthest from the center of a circular beam contributes the most resistance to torsion and deflection. The material at the exact center of the beam contributes no resistance to torsion or deflection.

Boring out the center reduces weight without sacrificing strength, which results in a higher strength-to-weight ratio.



Edited 1 time(s). Last edit at 10/29/14 15:46 by johnacraft.

A few close-up shots of 2156's running gear ....

Regards,
Burlington John

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DWDebs/2472 Wrote:
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> Piston rods on modern steam power are a
> hollow-bored, heat-treated steel forging. The
> material and heat-treatment specs are known. Same
> situation for steam locomotive driving wheel
> axles. Neither are not exorbitantly expensive to
> have custom-made. For 4-6-2 S.P. 2472, we had a
> new driving wheel axle forged from the correct
> type of steel, hollow-bored, heat-treated, and
> rough-machined. It cost a couple of thousand
> dollars.

Thanks Doug. Pretty interesting stuff. I don't want to say anything that might reveal my ignorance, but I'm curious about the order of the steps. Once you forge the material, does it get turned on a lathe to get the outside diameter? I guess boring would be next before the heat-treating. Does a piece sometimes warp making it unusable? You say rough-machined. I guess you still have the final machining to do at your own shop.

One of the tricks with machining is keeping reference points. Another is keeping things straight.

You forge something like an axle by taking a billet of iron, heating it up so it is soft, and smashing on it repeatedly as it cools to get it to be the general shape you want. You probably have to heat it up several times.

Iron is a crystalline material. As it cools it forms crystals. Since it is a mixture of stuff, the crystals tend to move the various impurities around, pushing them to the edges of the iron crystals. Depending on how slowly things cool, and what temperature they are at, you get different crystal patterns. Banging on the iron (like forging) tends to break up the crystal structure and mix things up. That is one reason forgings are more ductile than castings and less likely to crack.

After you forge the part, it has all kinds of embedded strains from being banged on. So you heat treat it for a while to let the strains even out, while not giving the iron too much of a chance to form big crystals. At that point you have something that is close to the right shape, and you can start machining to a finished size.

To make an axle, you probably start by roughly squaring off the two long ends of the rough axle. Then you can find the center of the bar and drill a cone-shaped pilot hole or center. You drill another center hole on the other end. Now you can carry the axle over to a lathe and chuck it up between centers. The tail-stock will have a cone-shaped "center" point that will exactly fit in one of the holes, and another center will be placed in the lathe spindle, exactly on center in the spindle. The line between the two center points will be the exact centerline of the finished axle. At this point the axle will spin on the centers. You clamp a "dog" on the end of the axle blank. This is a hollow clamp that goes over the end of the axle blank, and has a leg sticking out to the side. This leg goes in a notch in the "face plate" on the lathe. The face plate screws onto the spindle, and when the spindle turns, makes the axle turn.

Now you can rotate the axle exactly around a center line. You now rough-machine the outside bearing surfaces on the ends of the axle. You might take some stock off of other parts of the axle too, but unless you need contact surfaces that generally is a waste of time; the forging process should have got the axle close enough to the right size.

Once you have the bearing surfaces turned (a little oversize) you now move the axle to the grinder, which will again mount it on centers and will smooth up the bearing surfaces and get them exactly the right size. At this point the axle is finished, but it is too heavy, we need to hollow it out. We can now move it back to a lathe or boring machine, and chuck it by the bearing surfaces. (This might be done before finish grinding.) you can now drill a hole through the length of the axle, and then using a boring bar make it bigger. Since you are chucked on the bearing surfaces, the hole is concentric with the bearings, and therefore the axle weight is evenly distributed. If you didn't bore the hole on center the axle would be heavier on one side than another, and this would be bad for the bearings, if nothing else.

Note that you can't easily bore the center hole before you machine the outside bearing surfaces. If you do, you lose your center reference, unless you have some very special centers made (which could be done). If you don't have a good axle center reference, it is hard to get the bearing surfaces truly parallel and centered, as they need to be.

Fantastic information, thank you.

lwilton, thank you very much for the detailed response. I now have some understanding of the whole process in making a piston rod.

The main difference with a piston rod is that you will grind it full length, and you might do this with a machine called a "centerless grinder". That is a machine that will rotate a bar-like shape to make it round (and an exact size) without needing center points, so the grinding can be done after boring the rod. The result might not be absolutely balanced, but since piston rods go back and forth rather than spin fast, a little imbalance is no problem.

Bore it after you grind it, we've done tons of it at our facility
in Great Falls.

Out