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topic: 2784Entry straight on a (L)NER B7
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posted: 12 Nov 2015 17:03

from:

DerekStuart
 
United Kingdom

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I tried to resist the temptation to ask more about this, but I failed.
This is a follow on to an interrogation of Martin last week, but comments welcome from anyone.
Martin explained the reason for a long entry straight when a crossing was 'flatter' than its switch. The NER used for 1:9 upwards for a B, but also on a 7 but not a 7.5 (with a B8 being 'natural').
I have purchased a copy of BRT3 as recommended, but in the meantime the table I have doesn't show a B7 straight entry. I have a photo that I know is a B, but due to perspective (and correction tools have not helped) I cannot tell its vee. It has an entry straight of AT LEAST 8'6", which is too short for a B9. I'm hoping the B7 entry straight will either match up with the photo or be clearly not a match, either way I can tell which it is.
According to the books from the NER Association, it seems that the (L)NER seemed to use 0 entry straight- ie generic turnouts as its primary choice.
Many thanks for any info.Derek

posted: 12 Nov 2015 18:20

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Hi Derek,

What is your actual question? :?

If you now have BRT3 you should have the fold-out Table 16 at page 116. Here is a bit of it:

2_121255_420000000.png2_121255_420000000.png

You can see that the LNER B-7 has an entry-straight of 1ft-5in, with a corresponding reduction in lead length and radius compared with other companies' B-7s which don't have an entry straight.

The B-9 is showing an entry straight of 9ft-8in so that the turnout radius does not exceed the 613ft B-switch radius. The 9ft-8in figure corresponds with the B-9 in the NERA 1926 book.

It is important to bear in mind that track on the ground may not comply with the standard drawings after renewals. For example supposing the original turnout was an old NER switch. If it was later being renewed with a B-7, in order to match the existing points rodding it may need shortening to fit. The relaying inspector can do that by increasing the length of the entry straight. Try it in Templot -- SHIFT+F11 mouse action increases the entry-straight which shortens the turnout, which can seem counter-intuitive until you try it. :)

Likewise a turnout lead length can be increased from the standard length by inserting a straight between the heel of the switch and the turnout curve. However that is not common in the UK and Templot doesn't support it except using partial templates. It is more common in the USA.

regards,

Martin.

posted: 12 Nov 2015 19:11

from:

DerekStuart
 
United Kingdom

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Thanks Martin, that's just the info I wanted. I haven't received my BRT3 copy through the post yet.

You've explained entry straights in quite some detail now and that is very much appreciated.

I appreciate that "non-standard" track can be infinite, but on balance of probability I am more inclined to think this is a B9 rather than a B7 as a small point rod alteration would surely be easier than a one-off turnout. EDIT: I think I am in danger of turning research into an addiction. It could be either.

As always, I am in debt to you for your kind help.
Derek
Last edited on 12 Nov 2015 19:28 by DerekStuart


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