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Baldwin and balancing driving wheels

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Baldwin and balancing driving wheels
Posted by Aurora SL 1 on Sunday, May 14, 2023 7:35 AM

The return of AT&SF 2926 to steam - a brilliant achievement on the part of all involved - has got me thinking about big Baldwin steam locomotives and two other classes in particular: the New Haven I-5 Hudsons and ACL's 1800 class 4-8-4s. 

I have read many times that Santa Fe Northerns, particularly the last couple of groups built, including the 2900s, regularly ran at speeds in the 90mph to 100mph range, without any issues with track damage due to incorrect balancing of the driving wheels. Of course, other groups of big locomotives also operated at very high speeds without apparent damage to the track - Santa Fe's own Hudsons and Union Pacific's 800's sping to mind.  

As many of you reading this will know, the I-5s and the 1800s had problems with wheel balancing that both damaged the track and limited their maximum speed to 80mph, I believe. Although the issue was more or less fixed on the 1800s, my understanding is that the wheel balancing problems with both groups of locomtives were so bad that their respective owners lost faith in the locomotives.  

After that long introduction, my question is this: how could Baldwin get the balancing right on the driving wheels of the Santa Fe Northerns (and other classes of locomotives) but have problems with the NH and ACL machines?

 

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Posted by BaltACD on Monday, May 15, 2023 7:44 AM

First off - I don't know.

Could it be that Baldwin offered 'High Speed Balancing' as a "Extra Cost Option" like we consumers may get at some tire shops?

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Posted by CSSHEGEWISCH on Monday, May 15, 2023 10:15 AM

Balancing on a steam locomotive is more of an art since both rotating and reciprocating masses must be balanced.  Rotating masses (side rods) are not difficult to counterbalance but the main rods are a combination of rotating and reciprocating masses so cross-counterbalancing is also involved.

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Posted by timz on Monday, May 15, 2023 12:43 PM

Little or no art involved in balancing -- mostly just science (and math) that's too tough to figure out.

Among fans, the ACL 4-8-4s are famous for being built with bad balancing, presumably meaning with too much hammerblow. No one's heard about UP or SFe or SP or etc etc 4-8-4s being badly balanced. So what was different about ACL's? Baldwin built the SFe 3765s and ACL 1800s about the same time; probably they could balance the latter just as well as the former. (Maybe better, since the SFe engines had larger pistons due to their 60% limited cutoff.) So was it the railroad's fault? Did ACL give Baldwin bad instructions, and Baldwin did what the customer wanted?

RME article on the ACL engines

https://babel.hathitrust.org/cgi/pt?id=mdp.39015023098968&view=1up&seq=563

says 40% of the reciprocating weight was balanced, which doesn't seem way high. Main drivers were cross-balanced, of course. So the answer to the original question is: we haven't the faintest idea.

By the way: some SFe 4-8-4s were authorized to do 90 mph, or later 100 mph; NY Central allowed their passenger engines 85 mph. Don't think any other US railroad had a 4-8-4 timetable limit over 80.

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Posted by BaltACD on Monday, May 15, 2023 7:44 PM

timz
...

RME article on the ACL engines

https://babel.hathitrust.org/cgi/pt?id=mdp.39015023098968&view=1up&seq=563

says 40% of the reciprocating weight was balanced, which doesn't seem way high. Main drivers were cross-balanced, of course. So the answer to the original question is: we haven't the faintest idea.

...

Reading down through the articles following the ACL engine were interesting.

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Posted by Overmod on Tuesday, May 16, 2023 11:48 AM

The problem as I understand it was that Baldwin used an AAR-approved 'balancing formula' which really didn't apply correctly to modern (post-Eksergian) practice -- the figure I recall was something like 33 and a fraction %.  This would have been applied via Johnson's center-of-percussion method, perhaps without angling the balance weights as was IIRC practice on the 3765 class.

Johnson does not mention dynamic balance of the mains, either with bobweights or rods, and I get the impression that that practice was something the English did to high-speed express engines of minimum weight, not in the United States (even on the Milwaukee As which might have benefited from it).

Certainly this was in the relative infancy of high-speed 4-8-4s, and it was not yet then realized (or perhaps even suspected except by certain people like Voyce Glaze) that much of the need for formal overbalance is far better accommodated in leading and trailing truck lateral, applied as far toward the ends of the frame polar moment as practicable, with a relatively long driver wheelbase with controlled lateral.  That permits the adoption of the type of balancing used on the British 9F class, which is well worth studying, and in fact even the zero-overbalance that the Australians played with on extremely lightly laid lines toward the end of steam.

Unless I'm mistaken, the unbalance problem was rapidly corrected, probably by Baldwin, and the engines subsequently ran over 80mph with no tendency for track-wrecking.  So in my opinion little was wrong aside from adherence to an established but outdated standard.

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Posted by Aurora SL 1 on Sunday, May 28, 2023 4:39 AM

Thanks for your responses, everyone, they have answered my questions. I also went back to William Withuhn's book American Steam Locomotives: Design and Development 1880 - 1960. Withuhn does make brief mention of the 1800s but not in as much detail as some of the posted responses, so thanks again. 

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Posted by Overmod on Sunday, May 28, 2023 3:33 PM

Something fun to consider is looking at the 'other' 1800s, the period before the turn of the last century, at the time speeds approaching 100mph began to be achievable.  A fairly common 'fad' in those years was to divide the balance weight and move the two pieces to an angle with each other relative to a line through the axle center and crankpin.  This was said to reduce the actual vertical augment from overbalance somewhat, and I suspect reduce some of the torque in the axle that crossbalancing sets up.  I have not yet found discussions of the theory and practice in the contemporary trade press, but I strongly suspect they were there and would make informative reading today.

 

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Posted by Aurora SL 1 on Wednesday, May 31, 2023 6:39 AM

I didn't know about that at all, it sounds pretty fascinating. I did want to return to something you wrote in an earlier post, Overmod:

Certainly this was in the relative infancy of high-speed 4-8-4s, and it was not yet then realized (or perhaps even suspected except by certain people like Voyce Glaze) that much of the need for formal overbalance is far better accommodated in leading and trailing truck lateral, applied as far toward the ends of the frame polar moment as practicable, with a relatively long driver wheelbase with controlled lateral.

In the book I mentioned, Withuhn makes this oberservation about the N&W 'J' class 4-8-4s: 'So the N&W designers greatly stiffened the lateral resistance built into the centering devices of the J's lead truck and of its trailing truck. (Pg. 94)

Is this the sort of thing to which you were making mention in the quote I took from your post.?The Withuhn quote is from a longer discussion about N&W requring a passenger locomotive that developned optimal horsepower in the 40 to 60mph range (hence the 70 inch drivers) but could sprint up to 80 mph where possible on the N&W. (And as we all know, very much faster on test on the PRR). 

 

 

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