Measuring 3 1/2″ gauge

[Eric CoxParticipant @ericcox50497]

When measuring the 3 1/2 " across a pair of wheels, where should the dimension fall. ie, to the centre of the wheels or to the outside of the flanges.

[Eric CoxParticipant @ericcox50497]

[WearyParticipant @weary]

The flat side of the rail should lie just inside point P on this drawing.

The drawing gives enough info' to sort out your gauge dimensions.

Regards,

Phil

[julian atkinsParticipant @julianatkins58923]

hi eric,

the right hand position of 'P' on phil's excellent link determines the gauge. the root ie radius on the flange to tread should be inside the 'gauge dimension' of 3.5"g. however take phil's excellent link with a bit of caution as very few 3.5"g designs show either an adequate root radius or a taper on the flange, or for that matter a taper on the treads.

in theory the root radius should start at the gauge dimension. with the old fashioned steel strip rail this was rather essential otherwise you would be tight on the gauge. with vignoles section steel rail on most club tracks these days, which have a curved edge to the railhead, you should be able to push the wheelsets over sideways 1/16" if not more across the rails.

cheers,

julian

[Gary WoodingParticipant @garywooding25363]

Just to show what an ignoramus I am, what is dimension "B"?

Gary

[WearyParticipant @weary]

B = 'Back to back'.

Happy measuring!

Phil

[Eric CoxParticipant @ericcox50497]

"B" is the distance between the backs of the wheels. As a fraction it's 3 9/32"

[Neil WyattModerator @neilwyatt]

With my modest experience of wheel making, I have used the back to back dimension as my reference, putting shoulders on the axles.

I've done this for both 3 1/2" (loco) and 5" gauge (driving truck) and to my surprise they both work!

Neil

[Gary WoodingParticipant @garywooding25363]

Got it. Thank you.

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