question about the centipede tender axles on 3900/4000 series

[Dmacleo]

Hello, long time reader first time poster. often when you look a photo of the centipede tenders, especially when clean. the axle end caps look like they are canted while the actual wheel do not appear to have any cant to them. is this just an optical illusion or are the end caps canted? if so why? I am thinking they are for lubrication reasons possibly? been searching for weeks for answer but not found anything. Thanks Dave M

[Overmod]

End caps are canted; they have nothing to do with the bearing structure itself, which is not canted.  Do not be fooled by pictures you may see on the Web of locomotives with canted drivers; they are fantasy.  There is no particular point in providing negative camber to the wheels themselves; that is done by coning the tread when desired.

Yes, having the 'cant' provides additional oil reservoir area at the 'bottom', where it is more needed.

Something else to note about those centipede axles is that they are not rigidly aligned in their pedestals.  In between the axlebox and the little double spring going to the equalizing levers is a flat 'Fabreeka' spring, made of alternating plates of metal and an elastomeric material.  This allows the axles to move sideways under restoring control without compromising vertical weight bearing or suspension characteristics.  If you wondered why the centipede tender tracks so very well at high speed... that's a large part of it.

(Of course, the lateral compliance is still limited, so backing the tender up on a sharp curve will still lead to wheels popping into derailment... but that's another story.)

BTW the 1947 edition of the Locomotive Cyclopedia has some fairly extensive coverage of these pedestal tenders.

[Dmacleo]

Thanks, I was never able to get a close enough look to see if it was just the caps themselves (as I suspected) or more but was able to see the wheel themselves were not. And since I could not fathom any reason why the wheels would be canted (as that would have introduced tons of axle issues) it only made sense that it was the end caps. always suspected it was for reservoir reasons but just could not prove it to myself. I had read that the axles had "special" spring setup but had not known the name, will try to look into that cylopedia. Thanks Dave M