David,
If you imagine your wheelset going through a crossing, if the face of the flange just kisses the nose, the distance from the nose (essentially the running rail) to the face of the flange is zero.
Adding your dimensions, the distance from the running rail to the back of the flange must be 0.5mm.
The distance to the back of the opposite flange is another 19mm, therefore 19.5mm. The checkrail therefore, needs to be at least 19.5mm from the running rail in order to pull the wheelset clear of the nose..
Where you have two check rails, each 19.5mm from the opposite running rail, the distance over them would then be 18mm. As the back to back is 19mm, you have 1mm to play with. This can be used to reduce this clearance by moving each check rail closer to it's nearest running rail which will also pull the wheelset away from the nose.
If you move each checkrail out by say 0.3mm, the distance over them is 18.6mm giving you 0.4mm clearance from the back to back, and pulling the flange 0.3mm away from the nose.
So I would suggest setting each checkrail 19.8mm from the opposite running rail.??This is the check rail gauge and should always be used for setting a check rail. The flangeway is a derived figure and will vary as the gauge varies, whether by mistake or purposeful gauge widening.
Or do as Marc suggests.
Dave.
