Northumbrian Cylinder Centre Line Discrepancy?

[John RothwellParticipant @johnrothwell]

I have just started this build and I think I have encountered a discrepancy that no other builder has mentioned. The (revised) frame drawing shows the axle end of centre line of the cylinder terminating 1/2" up from the bottom frame edge. However later in the series (Issue 4368 31st December 2009 page 15) when describing how to fit the cylinders to the chassis the author states: "The outer end of the piston rod should be in line with the centre of the leading axle when this is at working height, 9/16", above the bottom edge of the frame".

Taking the driving and trailing wheel diameters and assuming the trailing wheel axle is designed to operate in the centre of its horn slot, confirms that the 9/16" dimension for the driving axle is correct. i.e. the (revised) frame drawing is in error in this regard.

Has anybody else pondered this? I have drilled my cylinder fixing holes in the frames so I seem to be faced with them being at the wrong angle relative to the frames.

[John RothwellParticipant @johnrothwell]

Is there a further error on the frame drawings?

[Ady1Participant @ady1]

What are you building?

Ah, the "topic" doesn't carry

It's a Northumbrian

Edited By Ady1 on 03/06/2014 10:58:05

[John RothwellParticipant @johnrothwell]

That's correct. I posted under the Northumbrian topic and assumed it would appear thus to everyone viewing. Apologies if this was not clear.

[Michael GilliganParticipant @michaelgilligan61133]

It does appear in the "directory path" at the top of the thread; but unfortunately that's in a rather small font, and positioned above the sponsor's advertisement.

MichaelG.

[stan pearson 1Participant @stanpearson1]

Hi John

I don't know about the loco you are building but as a general rule the centre line of the cylinder should meet the centre of the driving axle, the one that the connecting rod goes to.

Regards

Stan

[julian atkinsParticipant @julianatkins58923]

hi john,

i dont think on Northumbrian it will make much difference to the working of what is quite a simple loco.

cheers,

julian

[Phil H 1Participant @philh1]

Hmm, Im not far from this step so I will take care but as Julian suggests – will 1/16" matter when the axlebox moves in its horn by a greater amount?

PhilH

[julian atkinsParticipant @julianatkins58923]

on lots of GWR standard designs the cylinders are not inline with the axle centre line/working height of same and are 'out' by 2.5"! (the valve gear setting of the eccentrics is slightly altered to match).

cheers,

julian

[doubletopParticipant @doubletop]

I'd go with the 1/2" on the drawings. That would mean the bottom of the axle box is riding on the springs 1/8" off the hornstay. You don't want the axle box running too high as you run the risk of the eccentrics fouling any wood strip cladding you may install

Pete

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