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                                       switch block chairs conundrum
     
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1st message | this message only posted: 23 Jan 2016 12:12
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from:
Martin Wynne
West Of The Severn, United Kingdom



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This is copied from the 3D printing topic:

 http://85a.co.uk/forum/view_topic.php?id=2734&forum_id=6&jump_to=19858#p19858


Andrew Barrowman wrote:I think there must have been two varieties of L and R block chairs, one for each hand of turnout, but I could be entirely wrong.Hi Andy,

I can't find any evidence for that in any chair drawings or the chair type-designations. See the drawings on this page and the notes at the bottom:

 http://www.scalefour.org/downloads/gwrtracknotes/R1738.pdf

(my copy of this has "Amended 1957 ... Jun. 1961") at the bottom right).

The note makes clear that the L and R in the designation refer to each half side of a single switch. There is no reference to the hand of the entire switch. Indeed there is no need for any different chairs by the simple expedient of skewing the block chair on the timber. This is obviously acceptable practice (despite the slight loss of gauge-spread resistance) because it is done for the P slide chairs.

That page is for GWR and BR(W), but given the use of the same designations and the BR revision dates it seems likely that the BR REA designs are similar.

But here is a drawing of an REA left-hand A-switch:



Which shows the P slide chairs skewed, and the block chairs square-on to the timber (with no designations on the chairs that they are for a left-hand switch only). :?

I can only assume this was an error on the original drawing, and that all subsequent drawings have copied the same original.

Note also in that drawing the wider S1J joint chairs on the first timber.

This photo shows on the right an REA block chair on a right-hand switch. I wouldn't want to swear in a court of law that it is skewed to the timber, but it certainly looks that way:



This location is easily accessible, so I will go and have a closer look.

On the left a bolted half-chair is used to allow space for chairing the long check rail behind it (the actual reason for taking the photo :) ).

Here is a wider view. L1 bridge chairs on the left (on all 3 rails):



regards,

Martin.

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2nd message | this message only posted: 23 Jan 2016 19:16
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from:
Andrew Barrowman
USA

 

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Hi Martin,

I think you are right. The chair in that shot does look as if it's skewed. If you are able to read the designation on the chair that should clinch it. Failing that take a birds-eye shot of the turnout with your drone :)

Also, there is a note at the bottom of R1738 that says the R and L chairs apply to both RH and LH switches.

Come to think of it would seem a bit silly to produce chairs for both hands of switches when a small amount of chair skew will work just as well.

Regards,
Andy
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3rd message | this message only posted: 23 Jan 2016 19:19
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from:
Andrew Barrowman
USA

 

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I think I just repeated what you said about R1738!
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