Russ Elliott wrote:andrew jukes wrote:An S4 wheelset with a 17.87mm BB running through a turnout built to P4 standards i.e. using a check gauge of 18.15mm violates condition 2 of the Digest: BB (17.87mm) + EF (0.38mm) = 18.25mm i.e. >18.15mm, so the wheelset is likely to conflict with the crossing nose.
Hmmm. 'Conflict' with the crossing nose is a spectrum, and, as the Digest condition 2 points out, a problem is likely to occur only where the value of BB plus a small proportion of EF starts to approach the CG value. My view is that the shape of the flange front, together with dressing of the crossing nose, makes it unlikely that a P4 CG of 18.15mm would give rise to any significant problem. That said, I do agree with you that using a CG of 18.25mm is a more sensible approach if using wheel BBs above 17.82mm.
which conflicts with Martin's repeated insistence that BB+EF must not be greater than CG - to an insistence that even a 0.01 excess is unacceptable.
While I understood the prototype to exceed the CG by 1/32" it seemed plausible that what Russ' words here describe could occur at full size; if not, I could not see how, Russ, you could be promoting this idea, which you have before, and which seems so contrary to Martin's prohibition, viz:
not less than 17.57mm,
not more than 18.15mm minus the effective flange thickness.
With the best results if you get as close as possible to the latter dimension without ever exceeding it.
In other words 17.75mm works only if you can rely on the effective flange thickness not exceeding 0.40mm.
However I now see the source of your approach Russ - this famous Clause 2, (the new bit of which I will have to have explained in very simple terms if I need to understand it...)
I think what the new bit of Clause 2 is about is what all this was about (though the discussion today has left me behind completely), how to get the checking down to the same amount as the prototype. I am sure I'm on a completely naff level compared with you guys, practically, as well as intellectually; however, here, from my bargain basement perspective, is a loco being checked on the outside road of a curving turnout (without switch rails). The checking is occurring about 2 seconds into the video. This must be about as bad as it gets - 600mm curve and some ridiculous crossing angle. I don't see what the problem is really. These wheels were set on the 17.67 artefact and came out slightly less than that, around 17.64. I already showed on the previous page (Sun Apr 30, 2017 10:33 am) the "turnout" and a train of wagons zipping through it as though nothing was there at all, at a crazy speed for such a bend, with not the slightest sign of derailment on many repetitions - nor buffer locking, AJ uncoupling problems...I do understand however the latter problems reduce as sideplay decreases.
[youtube] lrXkgC5vph8 [/youtube] (have I done it right this time I wonder?....)