I'm just a novice so I need to ask the dumb questions. Why do many "original" photos of steam power show spoked pilot wheels but photos of the same locomotives in later years have solid wheels. The same seems to be true to a lesser degree of drivers. I've heard the term "Scoggin" driver. This seems to be a center driver of solid construction.<br>Did technology changes mandate these modifications? As always, thanks for your insight.<br>



shawsrus@dellnet.com

I am not sure of the reason for replacing spoked pilot wheels. I believe that some of the spoked pilot designs actually had "tires" shrunk on. It may have been easier to just replace the whole wheelset than mess with steel tires.<br>I am sure of the reason for replacement of the spoked main drivers with disc-type drivers. The main driver is subjected to a lot of stress due to its location relative to the rotating main drive rod. This stress often resulted in cracking of the spoked drivers. The PRR K-4 #1361 has spoked drivers and upon its initial restoration had to have numberous cracks repaired after non-destructive testing revealed cracks. The Frisco #1522 and Soo Line #2719 run in excursion service today with main driver as a disc and the remaining ones as spoked. <br>There were several types of disc drivers. One was called Boxpok and was commonly applied. There was also Scullin disc divers that look like swiss cheese (see Frisco #1522). Frisco was a big user of this type. There was also a Baldwin disc type driver applied to many new Baldwin steam locomotives. I recall seeing a picture of a PRR K-4 with a set of homemade disc drivers - not too appealing looking to say the least. <br>If you look at the design of any of the disc type drivers, there is one common theme - elimination of stress risers by the use of sweeping curves. This is not to say that the disc drivers never cracked. The B&O 4-6-2 #5300 has a nasty looking crack on its Boxpok main driver.<br>I personally would like to see the 84" Baldwin disc drivers from AT&SF 4-6-4 #3463 running at 100mph!! Even 50mph would do. We can always dream. <br>Hope this helps.<br>



hubbard5004@msn.com

I think Paul Hubbard makes a reasonable answer as to why pilot wheels and main drivers are as solid as they can be. As one of the people that works on the Frisco 1522, I have looked at the main driver, or number 2 main, and never thought that it looked like swiss cheese. Why does Paul Hubbard think that it does look like swiss cheese?<br>



jim1522@aol.com

Jim, I didn't mean to be so vague. If you look at the main driving wheels on the Frisco #1522, notice how they are solid and have a few round holes through - like Swiss Cheese! I happen to really like the look of the Scullin disc drivers mixed with spoked on the 1522. <br>



hubbard5004@msn.com