Getting back to the topic of EM-SF…
From a practical point of view, one needs gauges, and not just for the wheels Back-To-Back. An 18mm track gauge should be fairly straightforward to make (I did not say easily!); is one available commercially? The EMGS standard for gauge widening on curves is 0.2mm maximum. This suggests ordinary EM gauges could be used, I recommend especially on turnouts; I tend to add 0.1-0.2mm in ordinary EM and wish there was an 18.4mm track gauge available (0.2mm may seem excessive but allows for the inclination of C&L chairs). The check gauge dimension should be 17.2mm per Martin Wynn; the EMGS standard is 17.25mm although he says the EMGS check gauge can be used (but not available from the EMGS Stores for some time!). Martin refers to a Check Span of 16.4mm which confuses me slightly; I guess that is track gauge minus 2x 0.8mm flangeways?. He further states that gauge widening should not be undertaken in EM-SF turnouts but from practical experience I suggest that is a potential recipe for disaster. I have found a mint gauge (Track Checking Gauge in the EMGS Stores) invaluable for identifying narrow spots in my dodgy trackwork (almost always in turnouts near the blade ends despite putting sets in). If you can get an equivalent one made for EM-SF, I recommend it.
In EM-SF you need to ensure the track gauge is a minimum of 18mm throughout. An EMGS standard wheelset will just (only just) sit with the flange root-radius on the rails . This means that any reduction in gauge will force the wheels to rise…. This should not really be a problem, except possibly at turnouts. The advantages are that there should be less sideways movement of stock (I imagine particularly effective for the smooth movement of bogie coach rakes), and improved coupling of AJs through better centreing of vehicles.
If I build a new layout, I might give EM-SF a go if I could get hold of some decent gauges.
On the use of gauges, I agree (!) with Paul. As to whether a sliding fit or an interference fit is best, it depends upon the gauge and its application. For a BTB gauge I tend to use an interference fit as I regard the 16.7mm BTB as a maximum; a standard 16.5mm EMGS gauge gives a sliding fit minimum confirmation. For an 18.2mm track gauge I would require a close sliding fit (as confirmed by a mint gauge).
When setting BTBs you do not want to end up with a BTB that is too narrow. Pulling driving wheels out to correct this can be a real pain. Do not leave the job until later, correct it straightaway. Plastic-centred wheels seem to expand and increase their grip on the axle over time. I find it a disaster to have to dismantle driving wheels after the initial fixing. Invariably remounted wheels give wobbly or looseness or quartering problems; I now always automatically replace such wheels with new ones.
- This reply was modified 1 month, 2 weeks ago by John Cutler. Reason: corrects mistype of measurement