While feeding my addiction on steamlocomotive.com, I was going through pictures of NYC Hudsons. Looking at the J3as with either Boxpok or Scullins, I realized I knew why Bokpox were popular, but not what the supposed advantage of the Scullins drivers. Were they just expanding on the Boxpok advantages?
Several other past threads exist on this general subject. As with so many other areas of technology -- these are different products by competing companies, each attempting to avoid potential patent-infringement actions while talking up perceived advantage to the 'target audience'.
Here is a reasonable illustration of a Scullin center for your reference (from Martyn Bane's site):
The arrangement of cores in a Boxpok driver is different; the emphasis being on the 'box spokes' rather than the continuous discs. In both cases you have an exaggerated amount of metal around the crankpin. and very firm support all around the rim. Relatively easy to position counterweights, including those for 'fine adjust' of cross-balancing, including (as noted in the ad) the lateral position of the counterweight in the driver center
Other designs of cast center, notably the SCOA-P and Baldwin Disc, didn't use internal cores in the 'spoke' area.
Meanwhile, the Web-Spoke center provided substantially the rim stiffness of a disc design while keeping the (much!) lower mass of a spoke-and-rim casting. Several railroads considered these 'interchangeable' with Boxpok and Scullin drivers, at least for non-main axles where very substantial and strong construction around the pin was essential.
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