A4 points out of 6 chain curves

Discuss the prototype and how to model it.
bécasse
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A4 points out of 6 chain curves

Postby bécasse » Wed Jun 24, 2020 9:11 pm

I have recently, for my own purposes, produced prints of right and left hand A4 points out of an approximate 6 chain curve. The prints available on the Society database provided the basis for these prints but hopefully these prints have been corrected to eliminate the printing size problem. The "straight" track follows a 6 chain curve except through the planed sections of the point blades and through the crossing where it has been plotted as straight. The result produces an attractive and prototypical compact point and, as such, might prove useful to others who don't or can't use Templot for track planning.
A4-6ch-RH.jpg

A4-6ch-LH.jpg

The couple of blue lines on each result from the setting up process and could not be eliminated easily - they should be ignored.
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andrewnummelin
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Re: A4 points out of 6 chain curves

Postby andrewnummelin » Thu Jun 25, 2020 7:47 am

A good initiative, well done.

Based on a problem I recently had with a printer not doing exactly what it should have done, may I suggest that, if possible, you add a scale rule in both x and y directions so the accuracy of the final print can be checked.
Regards,

Andrew Nummelin

bécasse
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Re: A4 points out of 6 chain curves

Postby bécasse » Thu Jun 25, 2020 8:37 am

andrewnummelin wrote:
Based on a problem I recently had with a printer not doing exactly what it should have done, may I suggest that, if possible, you add a scale rule in both x and y directions so the accuracy of the final print can be checked.


I do in fact normally do that (for that very reason) when creating drawings of my own from scratch but in this case I will be using them within a drawing software package (Inkscape) where I have created a little tool that enables me to check that the 18,83 mm gauge is correct (on straight sections, of course). When I print out, I add a specifically sized rectangle to the drawing just to check that the print comes out at 100,0% on both axes, but, in practice, my software/printer combination does seem to get it precisely correct every time.

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Martin Wynne
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Re: A4 points out of 6 chain curves

Postby Martin Wynne » Thu Jun 25, 2020 12:13 pm

A more compact turnout, with an easier radius, would be to use a 9ft switch instead of an "A" switch. Those "A" switches are "natural" at 1:7, and hence significantly mismatched at 1:4. Although you say A-4 is a prototypical size, and is in fact included in the REA list (but not for GWR or SR), I doubt very many actually existed. The vast majority of such short turnouts would have 9ft or 10ft loose-heel switches.

The ruling curve in the main road would normally run through the switch and crossing areas, it's not usual for those sections to remain straight in a curved turnout even in yards and sidings.

cheers,

Martin.
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bécasse
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Re: A4 points out of 6 chain curves

Postby bécasse » Thu Jun 25, 2020 12:42 pm

Martin Wynne wrote:A more compact turnout, with an easier radius, would be to use a 9ft switch instead of an "A" switch. Those "A" switches are "natural" at 1:7, and hence significantly mismatched at 1:4. Although you say A-4 is a prototypical size, and is in fact included in the REA list (but not for GWR or SR), I doubt very many actually existed. The vast majority of such short turnouts would have 9ft or 10ft loose-heel switches.

The ruling curve in the main road would normally run through the switch and crossing areas, it's not usual for those sections to remain straight in a curved turnout even in yards and sidings.


Obviously I don't disagree with anything Martin says but I prepared the design the way that I did because it both fitted my requirements and, almost as important, was easy to make using components readily available from the Scalefour Stores, it effectively being a standard A4 point that gradually follows a curve, albeit that I will find it easier to make with the crossing and planed area of the blades straight. In fact, I did initially plot the point using a consistent 6 chain curve baseline, but found that keeping two areas straight made surprisingly little difference to the overall geometry while definitely making construction easier. A good friend of mine who was a pw expert, and a very early adopter of P4, used to point out that few goods yards followed any of the hypothetical rules as p&c work there was made up by the local gang using whatever secondhand bits and pieces happened to be available. As long as it worked at 15 mph, derailments didn't occur too frequently, and any exit to a running road was trapped, just about anything was possible.

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Rod Cameron
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Re: A4 points out of 6 chain curves

Postby Rod Cameron » Sat Jun 27, 2020 12:02 pm

Martin Wynne wrote:The ruling curve in the main road would normally run through the switch and crossing areas, it's not usual for those sections to remain straight in a curved turnout even in yards and sidings.


Excuse me butting in here, but thanks for that comment Martin. I've had the discussion on straight sections in P&C crossings in curved roads recently and just gone the pragmatic route with what looks right and more importantly what works.

This is one of the diamonds on the station junction at Lewes, with both roads curving. There might be a short straight section on the right hand obtuse crossing, but I can't see anything on the far common crossing.

14676350402_17c296c69e_b copy.jpg


I haven't done this one yet, but I have done the diamond on the 'country junction', also with both roads curving.

IMG_4204.JPG
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Martin Wynne
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Re: A4 points out of 6 chain curves

Postby Martin Wynne » Sat Jun 27, 2020 12:12 pm

Rod Cameron wrote:This is one of the diamonds on the station junction at Lewes, with both roads curving.

Image

Hi Rod,

That's a great pic of a curviform ladder. Can I use it in the Templot docs? Thanks.

Note that the straight section of the K-crossing is not tangential to the ruling curve. It has been kludged into the curve for practical reasons of available components, as a straight chord across the curve, with a slight dogleg at each end. The ruling curve remains running through the formation.

I have many times tried to explain this to those who insist that switches and crossings should always be straight, but it's a difficult concept to explain. This pic does the job fine -- worth a thousand words...

cheers,

Martin.
Last edited by Martin Wynne on Sat Jun 27, 2020 12:22 pm, edited 2 times in total.
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grovenor-2685
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Re: A4 points out of 6 chain curves

Postby grovenor-2685 » Sat Jun 27, 2020 12:18 pm

Interestingly on the DLR we had turnout designs with both straight and curved crossings (we called them vees).
So the 4 designs specific to DLR were CV40, SV40, CV100 and SV100. For longer turnouts we used standard big railway geometry.
CV40 = Curved Vee, 40 m radius. etc.
For the most part the CV were used for junctions and the SV for crossovers, but there is at least one junction, at West India Quay where an SV40 is used and the straight bit through the crossing is very noticeable.
Regards
Keith
Grovenor Sidings

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Rod Cameron
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Re: A4 points out of 6 chain curves

Postby Rod Cameron » Sat Jun 27, 2020 12:47 pm

Martin Wynne wrote:That's a great pic of a curviform ladder. Can I use it in the Templot docs? Thanks.


Hi Martin

It's a crop of a photo I found on Google images searching 'Lewes station', I don't know what the copyright issues are.
Rod

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Martin Wynne
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Re: A4 points out of 6 chain curves

Postby Martin Wynne » Sat Jun 27, 2020 2:08 pm

Rod Cameron wrote:It's a crop of a photo I found on Google images searching 'Lewes station', I don't know what the copyright issues are.

Thanks Rod. I found it here:

https://www.flickr.com/photos/31890193@ ... otostream/

It's copyright Ian Nolan, so I will contact him.

cheers,

Martin.
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