[chalkykpoatdz]

Discussing check rail to stock rail gaps.
Discussing point blade to stock rail gap when open.

In order to achieve realistic track geometry what tolerances are practical for setting flange clearance. On the full size railway a flange way at the heel of the point blade is about 60mm. The opening of the point blade at the toe is about 110mm to 120mm.

I suppose if this were scaled down and adhered to in finescale only scratchbuilt stock would run due to the back-to-back wheel dimensions and thickness of flanges being critical in travelling over points.

 

[34C]

Welcome!

You have the essence of it. The true scale 4mm movement got going in the 1970s under the title 'Protofour' or 'P4' and has continued to develop and amass experience in the necessary technique. It's demanding in a number of respects; not least of which is physical space, due to the minimum radius requirements. I suspect pretty much everything you need to make a start can be found here:
The Scalefour Society

 

[kristopher1805]

Not got quite the answers to hand but do have somewhere, the gauge for OO is 16.5 mm but the back to backs of railway wheel pairs is 14.4 - 14.6 mm so in this case we have a 1mm approx flange either side but as there is a bit of tolerance then maybe about 1.3 mm

It doesn't look too bad as OO is 1 in 76 and you have 60mm rather than 76mm which equates to 0.79 of as mm in OO gauge

 

[Graham Plowman]

Welcome!

You have the essence of it. The true scale 4mm movement got going in the 1970s under the title 'Protofour' or 'P4' and has continued to develop and amass experience in the necessary technique. It's demanding in a number of respects; not least of which is physical space, due to the minimum radius requirements. I suspect pretty much everything you need to make a start can be found here:
The Scalefour Society

Today, P4 is basically a non-starter as the supply of track parts has basically dried up with one supplier selling out to another who seems to be intent on grinding the business into the ground!

I'd recommend 7mm scale, not P4.