Re: Silverton Northern No. 4 - main rod connection to 3rd driver

tgbcvr Wrote:
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> David Johnson Wrote:
> --------------------------------------------------
> -----
>
> > Both types have the main rod connecting to the
> > third axle.
> >
>
> Hi David, you mention something that has puzzled
> me. Why did most of the Rio Grande NG
> Consolidations have the main driver connected to
> the second axle, but some to the third? There’s
> always a reason for such things, and perhaps
> it’s buried in your driver spacing dimensions?
> The piston travel would be identical for drivers
> of the same size, but the leverage may be
> different?
>
> Cheers from a non-tech type,
> Ralph


They're two variants of the Baldwin catalogue-standard narrow-firebox narrow gauge consolidation. The pattern with the main rod connected to the third axle came about a bit later on (mid 1880's), although the two types were available concurrently according to the preference of the purchaser (witness the 1890's-built C&S consolidations built using the older arrangement). Connecting the main rod to the third driver potentially allows for more favorable thrust geometry. Altering the wheel spacing also allowed for a shorter driving wheelbase, meaning less flange wear on curves, and the wheel spacing was such that the frame could "dip" at the front of the firebox to allow for some added depth just before the tubes.