Someone once told me that speed was a determining factor but I tend to disagree as there are examples of both types in slow and high speed service. One interesting example is the N&W J class which I believe used a single for the first five (600-604) then two thereafter on what was arguably the most powerful 4-8-4 ever. My best guess would be that is has something to do with reduced friction/improved fuel economy but I honestly don’t know. Can anyone knowledgeable shed some light on this?
Thanks
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There's been all sorts of debates of the two "single guide crosshead designs, Laird and Multiple Bearing, versus the double guide "Alligator" design. As the OP noted N&W used the multiple bearing design on the first five J's (600-604), plus the first ten class A's (1200-1209). For the rest of those two classes they went to the Alligator design. I believe that they found the Alligator design to either be easier to adjust, or more rugged (or maybe both).
Meanwhile on the New York Central, the class L-4a Mohawks had Alligator, while the L-4b class has multiple bearing crossheads.
On the Southern Pacific, all of their modern power used multiple bearing crossheads, except the Cab Forwards, because with the reverse running of the drives, the mainrod would exert greater force on the lower crosshead guide of the Alligator crosshead, while using a multiple bearing crosshead would have had more problems because of that same issue.
Stuart
It’s just two different ways of accomplishing the same thing. Put the bearings on the top and bottom or put them all on top.
Stuart posted:There's been all sorts of debates of the two "single guide crosshead designs, Laird and Multiple Bearing, versus the double guide "Alligator" design. As the OP noted N&W used the multiple bearing design on the first five J's (600-604), plus the first ten class A's (1200-1209). For the rest of those two classes they went to the Alligator design. I believe that they found the Alligator design to either be easier to adjust, or more rugged (or maybe both).
Meanwhile on the New York Central, the class L-4a Mohawks had Alligator, while the L-4b class has multiple bearing crossheads.
On the Southern Pacific, all of their modern power used multiple bearing crossheads, except the Cab Forwards, because with the reverse running of the drives, the mainrod would exert greater force on the lower crosshead guide of the Alligator crosshead, while using a multiple bearing crosshead would have had more problems because of that same issue.
Stuart
Thank you for your response. Just for clarification, are Laird and MB the same? I’m guessing the name “Multiple Bearing” refers to the fact that a single support guide must be strong enough to endure thrust from multiple directions. Is reduced friction even a consideration?
Rich Melvin posted:It’s just two different ways of accomplishing the same thing. Put the bearings on the top and bottom or put them all on top.
Are we talking roller bearing? I thought this part of the mechanism was typically a well-lubricated slide.
PRR 5841 posted:Rich Melvin posted:It’s just two different ways of accomplishing the same thing. Put the bearings on the top and bottom or put them all on top.
Are we talking roller bearing? I thought this part of the mechanism was typically a well-lubricated slide.
What Rich means is, the Laird multiple bearing crosshead guide design places those multiple bearing slide surfaces above the piston rod, i.e. "on top". While the Alligator crosshead design has the bearing slide surfaces above AND below the piston rod, i.e. "on top AND bottom". Roller bearings are NOT involved in the crosshead guides.
PRR 5841 posted:Stuart posted:There's been all sorts of debates of the two "single guide crosshead designs, Laird and Multiple Bearing, versus the double guide "Alligator" design. As the OP noted N&W used the multiple bearing design on the first five J's (600-604), plus the first ten class A's (1200-1209). For the rest of those two classes they went to the Alligator design. I believe that they found the Alligator design to either be easier to adjust, or more rugged (or maybe both).
Meanwhile on the New York Central, the class L-4a Mohawks had Alligator, while the L-4b class has multiple bearing crossheads.
On the Southern Pacific, all of their modern power used multiple bearing crossheads, except the Cab Forwards, because with the reverse running of the drives, the mainrod would exert greater force on the lower crosshead guide of the Alligator crosshead, while using a multiple bearing crosshead would have had more problems because of that same issue.
Stuart
Thank you for your response. Just for clarification, are Laird and MB the same? I’m guessing the name “Multiple Bearing” refers to the fact that a single support guide must be strong enough to endure thrust from multiple directions. Is reduced friction even a consideration?
The Laird and multi bearing crossheads are two different designs. Santa Fe made the Laird on many of their modern designs, such as the 3751 class 4-8-4 (Santa Fe 3751 Laird crosshead). As you can see in the picture the Laird crosshead guide has two horizontal bars with a slot for the crosshead to hang out of the side.
The multiple bearing (MB) crosshead was used by many railroads, such as Union Pacific on their modern designs, such as the FEF-3 (844) (Multiple bearing crosshead on UP #844). On the MB crosshead guide the slot was beneath the guide, with the crosshead hanging below it.
I hope this was helpful.
Stuart
Very informative, thank you.
PRR 5841 posted:N&W J class which I believe used a single for the first five (600-604) ....
You are correct, yet the latest Lionel Legacy versions of both the 600 and 603 are shown in the catalog with Alligator guides. It may not matter to some, but that was enough to keep that $1450 in my wallet.
What is being overlooked here is the crosshead that existed prior to the development of the Alligator or Laird. In my many moves, I managed to lose my copy of Alfred W. Bruce's "The Steam Locomotive in America- Its Development in the Twentieth Century" - a must have for anyone interested in the subject, written near the end of of their long career.
Despite the subtitle, Bruce goes back to the earliest days of steam, with text and diagrams showing how each major component of the locomotive developed into its modern form. Look at the General, of 1854. Its crosshead was a four-bar design, neither Alligator nor Laird. In cross section, it was a square with each corner notched with a two-sided cut, looking like a fat cross with stubby arms.
If I had my Bruce, I could tell you when the Alligator or Laird types were introduced (and probably where and by whom - Bruce was comprehensive).
Glancing through my Prince ACL book, the four-bar type was widely used until the mid 1890s, which means most Americans and many early Ten-Wheelers, Moguls, Consolidations, and 0-4-0's had them. I see Laird-type (top guides) and Alligators appear in the 1880s, but not start becoming dominant until the mid-1890s.
Look at any American on display in a museum, and you'll see what I mean.
@Stuart posted:There's been all sorts of debates of the two "single guide crosshead designs, Laird and Multiple Bearing, versus the double guide "Alligator" design. As the OP noted N&W used the multiple bearing design on the first five J's (600-604), plus the first ten class A's (1200-1209). For the rest of those two classes they went to the Alligator design. I believe that they found the Alligator design to either be easier to adjust, or more rugged (or maybe both).
I just happened to looking through my copy of Class A - Mercedes of Steam and here is what I found. "N&W found that the lighter multiple bearing crossheads yielded more mileage between shoe relinings, but were harder to keep in proper adjustment, and cracked or broken shoes were more difficult to detect."
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