How to use blade filing jig?

Discuss the prototype and how to model it.
Derek
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Re: How to use blade filing jig?

Postby Derek » Wed Nov 04, 2015 5:30 pm

Thanks Martin

I was just about to post another comment for Julian that- after referring to another diagram (you can tell I've only just received the NERA stuff) that the vertical planing is the same length as the lateral planing.


As for things varying by company and era, here on the S4 site, LNER turnouts are shown with straight rails before the knuckle (this is called the 'entry straight'?) to the joint with the closure rails, whereas the NERA diagrams show with NO straight section before the knuckle ('generic' crossing in Templot. Yet I have a Ken Hoole photograph of 1940 (track relaid post 1925) with the straight section starting clearly at the rail joint.

So even official diagrams of the era aren't always right. I am assuming (bound to be wrong) that there must be a good reason for this straight section before the knuckle- perhaps it is found better to have the wheels travelling straight before the knuckle to reduce the strain on the check rail etc- otherwise all you are doing is tightening the curve un-necessarily; after playing about with figures in Templot the difference in curvature was quite surprising (to my non- maths minded brain).

Derek

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Martin Wynne
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Re: How to use blade filing jig?

Postby Martin Wynne » Wed Nov 04, 2015 6:01 pm

Derek wrote:So even official diagrams of the era aren't always right. I am assuming (bound to be wrong) that there must be a good reason for this straight section before the knuckle- perhaps it is found better to have the wheels travelling straight before the knuckle to reduce the strain on the check rail etc- otherwise all you are doing is tightening the curve un-necessarily; after playing about with figures in Templot the difference in curvature was quite surprising (to my non- maths minded brain).

Hi Derek,

By default, an entry-straight section (column A in the lead tables) is introduced in turnout sizes where the crossing angle is flatter than the "natural" angle for the switch. i.e. a B-8 and shorter has no straight, a B-9 does. (Except for the LNER only, where a B-7 also has a straight, but not a B-7.5 -- I mentioned about companies picking and choosing. Image )

The length of the straight is determined by the turnout geometry, the position of the wing rail front joint is not relevant.

The intention is that the turnout curve should not be an easier radius than the switch radius, otherwise you would have negative transition effect in the turnout road and a load discontinuity at the switch heel.

However an entry-straight may be added, or extended in length, in situations where it is required to shorten the lead of the turnout without changing the switch or crossing sizes. Typically this might be done to suit point-rodding runs, avoid culverts below the track, signal post siting, and similar obstructions.

In Templot things are a bit different, to allow for typical modelling circumstances. To create exact-scale 4ft-8.5in gauge turnouts in Templot:

1. make sure you are using an exact scale track gauge, i.e. there is no point in bothering in 00 or EM.

2. select a "generic" V-crossing where there is no straight, and a "regular" V-crossing where there is one.

3. change to CLM unit angle.

4. if a "regular" V-crossing, adjust the length of the entry-straight to match the prototype drawing using the SHIFT+F11 mouse action.

If you need more details of Templot adjustments, please ask on the Templot Club forum.

regards,

Martin.
40 years developing Templot. And counting ...

Derek
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Re: How to use blade filing jig?

Postby Derek » Wed Nov 04, 2015 6:25 pm

Thanks for the further comments, Martin.

I had already grasped and understood those points- but I'm sure they will be useful for others reading this.

My point is that there are two different diagrams relating to the same company, for the same turnout in the same era, although I take your point that there might be a very good reason why one is chosen over another for a very specific local reason.

(for the benefit of Julian, or anyone else, I think the table Martin refers to is http://clag.org.uk/protodata-bullhead.html ) This table shows that the only B's that have a straight section is a B9 or B10.... oddly a B11 does not. Most other turnouts are listed with NO straight, yet the S4 templates show them all as having them.

I think NERA book (or similar) + photo = Templot custom turnout is the right formula there.

Derek

EDIT: To remove a point that was already answered by Martin.

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Martin Wynne
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Re: How to use blade filing jig?

Postby Martin Wynne » Wed Nov 04, 2015 6:55 pm

Derek wrote:(for the benefit of Julian, or anyone else, I think the table Martin refers to is http://clag.org.uk/protodata-bullhead.html ) This table shows that the only B's that have a straight section is a B9 or B10.... oddly a B11 does not.

Hi Derek,

Yes, that is the table. However that web-posted version contains several differences from my "official" version (fold-out on page 116 of BRT3, dated 1964).

For example an LNER B-7 is shown with an entry straight of 1ft-5in and correspondingly shorter lead length and radius than other companies' B-7.

Only the LPTB is shown using a B-11 (an odd size really) and it has an entry-straight of 24ft-10.1/4in.

The main "error" on the Scalefour templates is the wrong position of the wing-rail front joints and the accompanying closed-up timbering. This has been much-discussed on here before. They were originally prepared by Exactoscale, and the "error" was explained by them as necessary for production reasons on their turnout kits (P4 Track Co, now C&L).

regards,

Martin.
40 years developing Templot. And counting ...

Julian Roberts
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Re: How to use blade filing jig?

Postby Julian Roberts » Thu Nov 05, 2015 11:07 am

Thank you all for your comments yesterday.
Sorry I have to be brief as I accidentally deleted an almost finished post, and duty calls.
Derek I could not find in the NERA link any immediate information re switches.
I basically get the impression from Martin and Keith that it is not worth trying to represent the undercut aspect neither for visual fidelity nor running reliably.
The conversation got onto staight sections.
As far as I can see the tables refer to straight sections in other parts of the turnout rather than the shape of the switchblades...? I will be happy to follow the Society Template for the rest of the construction. I do not have it with me but as I recall the switch area is not particularly clear, and I propose to follow Martin's earlier post about making B switch blades and stock rail set, and superimpose that on the template. Improvise to marry the two.
My main confusion is the red boxed part of Martin's photocopy.
"The top of the switch rail is also planed at the tip to a certain depth below the top of the stockrail RUNNING OUT in a length equal to the side planing". (My capitals.) Does that mean that the (very slight) slope up from .25mm reduction of rail height at the tip to full rail height takes place over the full 29mm of the B switch? I.e. contrary to Derek's info that it is over the first 12mm?

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grovenor-2685
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Re: How to use blade filing jig?

Postby grovenor-2685 » Thu Nov 05, 2015 12:17 pm

My main confusion is the red boxed part of Martin's photocopy.
"The top of the switch rail is also planed at the tip to a certain depth below the top of the stockrail RUNNING OUT in a length equal to the side planing". (My capitals.) Does that mean that the (very slight) slope up from .25mm reduction of rail height at the tip to full rail height takes place over the full 29mm of the B switch? I.e. contrary to Derek's info that it is over the first 12mm?

IMHO you are worrying to much. The purpose of this top planing is so that the tip does not cover the corner radius of the stock rail, it needs to extend to the point where the switch blade is thick enough to have a corner radius of its own. These are very difficult things to fully emulate in our scale, when filing the switch tip off at an angle as in Martin's nice diagram one or two additional file strokes will bring the knife edge down a tad at the tip. Testing this against the stockrail will reveal if its a bit high and you can file slightly bore or wait till it is installed then use a half round file to blend the switch rail and stock rail together.
Regards

Derek
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Re: How to use blade filing jig?

Postby Derek » Thu Nov 05, 2015 2:29 pm

Julian

I'm sure you will see the warning yourself, but just in case you have downloaded via a direct URL, the Society's templates are under scale and should not be used for construction without a slight enlargement (there is a link on the page to a discussion about it). Have you used Templot? Unless one is used to building real world track as a pway engineer, or has studied it in great detail, I think Templot is probably the most reliable way to design accurate track. Though the Society's template is good for identifying which chair goes where).

This is the page for the NER A that you need. There is a link on it with a PDF of all the titles available.

I recommend the following titles (in this order of importance)

Standard Railway Equipment - Permanent Way, 1926
NER Permanent Way Standards
NER Standards

The first two are about the actual track work (the 1926 one is the original LNER and the second one is the earlier NER one). The last one is mostly about line side fixtures and fittings.


TOP PLANING: As I said in a follow up post, I found a further diagram that shows the planing finishing just short of the side planing (though I would not argue that this should coincide exactly with the side planing as the diagram is a little old and hard to see). I don't know whether that 12mm refers to an earlier standard or specifically for that particular example.

Even in the titles listed above there are diagrams that contradict each other. No doubt to a p-way engineer at the time, it would be obvious which example would work in which location; although the above titles are fairly comprehensive they are not 100% complete and I suspect from the numbering there are explanatory notes missing. As I have found out over the last year that this is just as much art as it is science.

Derek


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