Re: Gnr251/Lner 3251
Posted: Thu Aug 22, 2019 11:03 pm
The gap on the GN Atlantics was very small.
One must remember tyre wear, which could be significant.
John
One must remember tyre wear, which could be significant.
John
Discussion and reference site for the London North Eastern Railway
https://www.lner.info/forums/
This is where the model maker's 'cunning plan' comes in. Very frequently the best way for a small scale steam model using RTR standard overscale flanged wheelsets is to design the mechanism around driven wheelsets at or near maximum permissible wear condition. Basically take a scale 2" off the nominal wheel diameter, and that usually buys enough 'wiggle room' where the wheelbase is very tight as on the GNR design atlantics. (6'7.5" nominal over tyres, 6'10" between axle centres: the 4mm model has correct wheelbase, enabled by this method.)drmditch wrote: ↑Thu Aug 22, 2019 12:20 pmA picture is almost impossible I'm afraid, owing to the footsteps being in the way.Hatfield Shed wrote: ↑Thu Aug 22, 2019 10:51 am Take a picture of the gap between the driving wheel flanges too, with a hand or something in the view to show scale.
I can tell you however (having attempted this previously) that I can only just get one finger into the gap.
This is about 14mm. (.55")
From RCTS Part 3A (6'8" wheel and 6'10" spacing ) gives a distance between treads of 1", but I think it is more than that.
Fortunately I'm not tempted by an ex-GN Atlantic for my NE Area railway. the long-term plan is for a V(C6) and/or possibly a Z(C07). Quick calculations from Part 3A suggest that the inter-driving-wheel clearance should be 4" between treads.
I'm just wrestling with a small problem on my A8 at the moment. (4.5" gap). With 5'9" wheels represented by 23mm Markits I cannot find any way to fit brake blocks!. (This is a semi-scratch-built chassis.) Next time I build anything like this I will definitely go for undersize wheels.
One little project I keep meaning to complete is to compare actual/plan sizes on several of the locomotives at Shildon. I can tell you that the Black Five is well under 6' and 4771 is definitely under 6'2".