Gnr251/Lner 3251

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JASd17
LNER V2 2-6-2 'Green Arrow'
Posts: 1095
Joined: Thu Nov 25, 2010 11:21 pm

Re: Gnr251/Lner 3251

Post by JASd17 » 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

drmditch
NER C7 4-4-2
Posts: 854
Joined: Sun Aug 01, 2010 5:55 pm
Location: Durham

Re: Gnr251/Lner 3251

Post by drmditch » Fri Aug 23, 2019 7:21 am

JASd17 wrote:
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
Indeed, and both 5000 and 4771 have run extensively in 'preservation'. I will try to find out when they were last re-tyred.

Hatfield Shed
LNER P2 2-8-2
Posts: 931
Joined: Fri Dec 23, 2011 3:34 pm

Re: Gnr251/Lner 3251

Post by Hatfield Shed » Fri Aug 23, 2019 12:12 pm

drmditch wrote:
Thu Aug 22, 2019 12:20 pm
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.
A picture is almost impossible I'm afraid, owing to the footsteps being in the way.
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".
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.)

And this makes for a more accurate model in my opinion. Every loco that has turned a wheel in service must be running on tyres below nominal diameter, because wear starts from the first outing on the line; and at each visit to the wheel lathe for reprofiling it is further reduced by intention.

drmditch
NER C7 4-4-2
Posts: 854
Joined: Sun Aug 01, 2010 5:55 pm
Location: Durham

Re: Gnr251/Lner 3251

Post by drmditch » Tue Aug 27, 2019 7:18 pm

I did manage some mobile-'phone pictures last Friday.

The first one shows the cut-out in the wheel-boss. I think that this is the driving wheel (rear coupled wheel). There is a similar feature on the leading coupled wheel, but it was more difficult to photograph.
Post_01.jpg
Next is the gap between the coupled wheels, as seen from just behind the central footstep.
Post_02.jpg
The next is not a good image, but it is the best I could do juggling the 'phone behind (inside) the footstep.
Post_03.jpg
Then it gets even worse! But my left index fingernail is 10.5mm across the cuticle.
(In case anybody wishes to use this as a modelling guide!)
Post_04.jpg
I have no idea what the letters 'RO' could refer to or what fitting would be in that position on the frames behind the driving wheels. Perhaps someone with knowledge of Doncaster practice can tell us!

drmditch
NER C7 4-4-2
Posts: 854
Joined: Sun Aug 01, 2010 5:55 pm
Location: Durham

Re: Gnr251/Lner 3251

Post by drmditch » Tue Aug 27, 2019 7:22 pm

All the above photographs are of the LH side.
Then there is a nicer and better photograph of the drivers side.
I can't remember when I took this, but it was some time ago. (We don't have the white footsteps any more!)
Post_05.jpg

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