oo-sf back to back dimension
Posted 04 May 2015 - 20:51
Apologies if this appears a daft question, but is a specific back to back gauge required for 00-sf, or can the same one that is used for 00 16.5 be used?
00-SF uses the same back-to-back as ordinary 00 -- but not the back-to-back gauge from C&L which is for DOGA-Fine only.
Posted 04 May 2015 - 21:19
So what dimension does it need to be, I have a feeling the one I have may have been sourced from C and L at some point in the distant past.
The optimum dimension varies with different wheels. Do you have a digital caliper? If you are not sure which wheels you are dealing with, measure the width of them:
Wheels 2.8mm wide -- back-to-back 14.4mm MAX. (RTR wheels)
Wheels 2.5mm wide -- back-to-back 14.5mm MAX. (Markits loco wheels)
Wheels 2.3mm wide -- back-to-back 14.6mm MAX. (Kit wagon wheels)
For 00-SF the MIN back-to-back is 14.3mm for all of them.
If you don't know which wheels you have, make the back-to-back 14.4mm.
In practice, if you have bought an 00-SF check gauge, you can do better than using back-to-back gauges by building yourself a wheel-testing fixture, like this:
This is how to use the gauges to create a wheel testing fixture:
Thanks to Dave (Acklam) for this picture.
1. Fix this rail first. It represents the crossing vee. There is a flat on the check gauge so that it can be used where the vee won't fit in the slot.
2. Fix this rail second, using the check gauge tool. It represents the check rail.
3. Fix this rail third, using the 1.0mm shim. It represents the wing rail. it doesn't engage with the check gauge tool.
4. Fix this rail last, anywhere you like. Its sole purpose in testing the wheels is to support the wheel. It represents the opposite running rail. A good way to identify it in future is to fix it upside down, or make it longer or shorter than the other rails.
Mark which rail is which. Don't get rails 1. and 4. muddled up.
In using the fixture,
1. hold the back of one wheel against rail 2.
2. gently lower the other wheel onto rail 1.
3. the wheel flange should just clear the side of rail 1. without rubbing, but ideally leaving only a fraction of daylight showing between them.
4. the back of that wheel should easily clear rail 3.
With care, a testing fixture like this if accurately made is a better way of setting the wheels than using a back-to-back gauge, because it allows for different flange thicknesses, and the actual track you are building.