Kato's SD90Mac has N scale 44 inch wheels (in theory), which in NZ120 scale out to 839mm, somewhat short of the 940mm needed for loco wheels (excluding the DA/DB/DBR/DC). Although of course the massive flanges help the illusion.
So after some research on the Northwest Shortline website I came up with the following options:
HO scale 28" wheels scale out to 991mm in NZ120, oversize by 0.46mm at scale size.
The closest size to ideal would be 27" (HO), 946mm in NZ120 which don't exist.
26" (HO) works out to 914mm in NZ120, undersized by 0.18mm at scale size.
The 26" wheels were the closest option, but only available with 2mm shouldered axles in /64 finescale.
I ordered some 28" /64 wheels which according to the ordering page had 1.5mm pointed axles, quite crucial for what I wanted.
However when they turned up they had 2mm axles, so I probably should have ordered the 26" wheels after all.
I also ordered a set of Kato SD90Mac wheelsets.
Briefly, the Kato wheels were disassembled and the plastic gear was modified to take the NWSL wheels. Since the gear has an outside diameter of only 2.4mm it was first given an "outer" of brass tube to give it a bit of strength and then drilled out to 2mm. Had I got wheels with 1.5mm axles I may not have needed to strengthen it first.
The NWSL wheels were intended as wagon wheels, so one wheel on each axle is insulated. This was removed, then the axle was cut short to make it a "half axle", these were then "pushed" into the modified Kato gear. Two wheelsets are needed to make one replacement loco wheelset so it's not an overly cheap option.
Some points we have discussed since doing this include:
The flanges look great but track work will have to be perfect if /64 is to be practical, it may be that we need to move to /72 for reliability.
We need to see if NWSL will sell us wheels in kitset form, that is with no insulated wheels included.
The pinpoints are obviously somewhat larger than the N scale originals and may not fit into existing N scale bogies easily. However following the close enough doesn't have to be good enough theory, that is not the intention...
3 comments:
I do like your sleeving option and it does make me wonder whether something similar could be done to create standard gauge TT mechs from N ones . . .
Looks like it is time I fired up the lathe and tried making some wheels from scratch, dunnit? Anyone else tried this yet?
Not from scratch, but i have ordered some 3' diameter spoked wagon wheels from the US which turned out nice, and gotten some loco wheels milled from scratch to replace some Farish coach ones whch a 2mm guy had milled for me but which got lost in the mail! I'm now thinking of whether it's better to get 8mm wheels milled than to bother with the Bachmann cheapie steam wheels I'd planned on using for some diesels with 3'4" dia wheels.
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