Question Re MPD Track Plan

Discuss the prototype and how to model it.
Proton
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Question Re MPD Track Plan

Postby Proton » Mon Jan 10, 2022 3:04 pm

I am building a steam MPD and as per the prototype the arrangement is fairly congested, but not impossible. I might have to install a tandem turnout using B-planing for the left turnout but A planing for the right - so it will be an A6R, B8L. I need the extra inch or so this gives to get the right hand turnout to enter the shed.

Two questions: is this at all prototypical, and would large engines (pacifics) be able to negotiate the A6?

Also, one of the roads into the turntable will be a 4'radius Is it ok for the track to come right off a curve, or should there be a short section of straight track?

Finally (for now!), I have a rather nice Bachmann coaling tower to use - does anyone know the correct track spacing for the engine and the wagon roads?

Ideas and Recommendations welcome, thank you!

John

davebradwell
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Re: Question Re MPD Track Plan

Postby davebradwell » Mon Jan 10, 2022 6:44 pm

Suggest that once you're struggling for the last inch you've lost already.

Wasn't a B6 the smallest point through which BR would run anything - sure I've seen that somewhere? Big 4 might have been less generous.

As you're bringing tracks back to parallel, you're making a reverse curve which can be a disaster for big engines if not done carefully. Depends how you build your Pacifics, of course - re-wheeled types will be far more tolerant than kit builds.

DaveB

JFS
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Re: Question Re MPD Track Plan

Postby JFS » Mon Jan 10, 2022 7:41 pm

Assuming you are drawing it using Templot (if not why not!) then you will find that considerably shorter switches than the A and B are are available - for emaple, using the GWR "Old type 9ft" will save you a fair bit even compared to an A switch and, if you are really pressed you can use the non-prototype model switch. Which ever you do use, few people will be able to tell once it is built!!!

Best Wishes,

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stephenfreeman
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Re: Question Re MPD Track Plan

Postby stephenfreeman » Tue Jan 11, 2022 10:45 am

JFS wrote:Assuming you are drawing it using Templot (if not why not!) then you will find that considerably shorter switches than the A and B are are available - for emaple, using the GWR "Old type 9ft" will save you a fair bit even compared to an A switch and, if you are really pressed you can use the non-prototype model switch. Which ever you do use, few people will be able to tell once it is built!!!

Best Wishes,

I would think it highly unlikely that any steam era MPD would have anything as modern as A or B switches, most likely to be anything else.

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Julian Roberts
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Re: Question Re MPD Track Plan

Postby Julian Roberts » Tue Jan 11, 2022 7:53 pm

Interested to know which MPD this is? It seems Kyle MPD had B switches on the tandem in BR days - it's plain that the switches are not loose heel in the photo at the bottom of the page here, - see the discussion there
viewtopic.php?f=9&t=7017

JFS
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Re: Question Re MPD Track Plan

Postby JFS » Tue Jan 11, 2022 8:48 pm

Julian Roberts wrote:Interested to know which MPD this is? It seems Kyle MPD had B switches on the tandem in BR days - it's plain that the switches are not loose heel in the photo at the bottom of the page here, - see the discussion there
viewtopic.php?f=9&t=7017


I see you are responding to Stephen Julian, but just to be clear, IIUC, the OP asked how could he shorten his turnouts to save an inch or two - that is not necesarily the same question as "what would the real thing use". Even if we choose to incorporate a prototype switch which may have been loose heel, it need not be modelled as such - what Templot does is to give you a good geometry despite whatever components you choose to throw in the mix. It does not force you to model them in the prototypical fashion. We are therefore at liberty to disguise our fudges in anyway we choose :D

Martin has pointed out many times that there are many situations (A5 being one) where that combination is neither the best geometric solution nor the most compact.

However, I support Dave's contention - just because it can be drawn in Templot does not mean that your Big Boy will go round it, though your 14xx might do!

John:- come on then! Show us your plan!!!

Best Wishes,

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Julian Roberts
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Re: Question Re MPD Track Plan

Postby Julian Roberts » Wed Jan 12, 2022 9:13 am

Yes Howard you're quite right, I was responding to Stephen's point and rather forgetting the OP question - sorry!

Having gone through a similar design procedure, and semi-learned to use Templot while doing so. surely if the real thing did something, it should be possible on the model? E.g. the 4' curve onto the turntable, and the tandem design. But the question is, how do you know what was actually there? The 100 yr old OS 25" map isn't necessarily gospel so must be interpreted by looking at photos. Trackwork evolved as it was renewed over the years, so photos are gospel only for that moment in time.

Maybe bigger locos didn't use the more sharply curved roads. Though I think in P4 most locos can be constructed in such a way they are able to go round that curve even if the real thing couldn't.

davebradwell
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Re: Question Re MPD Track Plan

Postby davebradwell » Wed Jan 12, 2022 9:29 am

Whether you can enter a turntable via a curve depends on the turntable. If there's girders on top then the swing of outside cylinder locos can clout the girders for starters. If there's the tiniest trace of backlash in the drive, when the first wheel goes onto the deck it will push the table sideways and the rest go on the deck. Somebody in our group has been there.

It wouldn't be unusual for some locos to be banned from some sdgs - WDs were barred from tracks because there was a danger of the tender derailing in reverse. In depends on your (secret) prototype.

DaveB

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Noel
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Re: Question Re MPD Track Plan

Postby Noel » Wed Jan 12, 2022 3:50 pm

There were sheds where the turntable was too small for some of the locos allocated or regularly visiting, so they had to go round a triangle to turn. Branksome was a case in point - the t/t would take a 2P 4-4-0 or 4F 0-6-0, but not 7F 2-8-0s, 9F 2-10-0s or large 4-6-0s, which had to go round Branksome triangle.

davebradwell wrote:Whether you can enter a turntable via a curve depends on the turntable. If there's girders on top then the swing of outside cylinder locos can clout the girders for starters.

Even on turntables with under girders there would normally be handrails to stop loco crew falling into the well.
Regards
Noel

Tony Wilkins
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Re: Question Re MPD Track Plan

Postby Tony Wilkins » Wed Jan 12, 2022 5:16 pm

Proton wrote:I am building a steam MPD and as per the prototype the arrangement is fairly congested, but not impossible. I might have to install a tandem turnout using B-planing for the left turnout but A planing for the right - so it will be an A6R, B8L. I need the extra inch or so this gives to get the right hand turnout to enter the shed.

Ideas and Recommendations welcome, thank you!

John


Hello John.
A further option to maybe consider is using a three throw turnout to save space, although they are bit of a pain to build and operate. They were used in MPDs occasionally.
Yes, B-6s were supposed to be the minimum unrestricted turnout, but even then I think there may have been some exceptions.

Regards Tony.
Last edited by Tony Wilkins on Thu Jan 13, 2022 3:15 pm, edited 1 time in total.
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Proton
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Re: Question Re MPD Track Plan

Postby Proton » Wed Jan 12, 2022 8:45 pm

Thank you all for your interest and replies. The MPD blank canvas is shown in pic 2998, and I generally find it easier to plan using the full size real estate in place, in this case 14' x 2', although 6' is notched to 17 inches wide. Pics 3007, 8, and 9 show green painter's tape as my first cut. The turntable is in place at the end, and the 4 road shed will be in the notched area. 40 " long, almost to the end. There will be two roads next to the shed - one for locos and one for coal/ash wagons. buffer stops will prevent drops onto the track below. Two tracks in front of the coaling tower will allow access to the main line (not built yet).

I don't use Templot, my own skills don't extend that far. However, I have created complex formations designed by others, and in that regard I find it outstanding.

By fine-tuning the placement of the turnouts I have found the inch I needed, and the final turnout approaching the shed is a simple B6R - B8L tandem, to the P4 template. It is fed by a B6 double slip, so all engines from the shed can be coaled. I was hoping to be able to access the spare real estate behind the coaling tower directly from the shed, but it would require turnouts just at the shed door - a bit silly.

The turntable will have multiple access points and I will create a few roads behind the tower to be accessible from the turntable.

I can send pics of the rest of the railway if there is interest.

BTW, this vaguely represents somewhere are Manchester.

John
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Proton
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Re: Question Re MPD Track Plan

Postby Proton » Thu Jan 13, 2022 3:51 pm

I have refined the track plan using templates, and it's starting to look good. I will start from the shed with the tandem, and work towards the mainline. I will need two "specials", the #3 diamonds presently omitted. The station terminus needing engines from the MPD is shown. The station throat was designed with standard P4 soc templates, Templot (courtesy of friends), and the curved scissors was designed by hand.

This will be analogue DC, common return, and driven from its own controllers.

John
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davebradwell
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Re: Question Re MPD Track Plan

Postby davebradwell » Thu Jan 13, 2022 10:00 pm

You'd be doing yourself a favour by using DCC as it's going to be a huge job wiring up those complex formations for more than one controller. It can be done of course, there was no option at one time, but it's much easier with DCC. It's the diamonds that cause the issues and you have quite a few of them: with DCC all the K crossings at the far side go to one terminal and those on nearside the other. With dc you have to switch them all between one route or the other (and avoid conflicts) in order to connect them to the right controller although perhaps half might go to your common return, I'm very rusty on dc these days. Then you'll be forever missing a section - it's bad enough getting all the points lined up. This from experience of King's Cross model - with DCC.

Here's another - When did the practice of a trapped loco from an incoming train having to follow the departing coaches to the end of the platform end? Presumably with later forms of signalling.

DaveB

MikeAllerton
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Re: Question Re MPD Track Plan

Postby MikeAllerton » Fri Jan 14, 2022 9:36 am

davebradwell wrote:Here's another - When did the practice of a trapped loco from an incoming train having to follow the departing coaches to the end of the platform end? Presumably with later forms of signalling.

DaveB


This was still common practice at Manchester Piccadilly throughout the 1970s. I'm guessing it continued until the introduction of driving trailers (probably wrong terminology) effectively forming fixed multiple units.

Proton
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Re: Question Re MPD Track Plan

Postby Proton » Fri Jan 14, 2022 11:23 am

Although DCC would simplify the wiring it would add an unacceptable level of complexity and cost (choice of system, decoder cost, decoder programming, reduction in space in locomotives for lead weight). The station is wired for analog and I dont find wiring diamonds and scissors particularly difficult. Four of the terminus roads have crossovers at the buffers to allow trapped locomotives to escape. Part of the fun!

J

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grovenor-2685
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Re: Question Re MPD Track Plan

Postby grovenor-2685 » Fri Jan 14, 2022 12:45 pm

davebradwell wrote:When did the practice of a trapped loco from an incoming train having to follow the departing coaches to the end of the platform end? Presumably with later forms of signalling.

I don't believe this was ever a signalling design issue, rather one of operating convenience, you want the loco out asap to clear the platform for the next train. Lasted AFAIK as long as loco hauled trains.
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Keith
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JFS
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Re: Question Re MPD Track Plan

Postby JFS » Fri Jan 14, 2022 4:24 pm

davebradwell wrote:Here's another - When did the practice of a trapped loco from an incoming train having to follow the departing coaches to the end of the platform end? Presumably with later forms of signalling.
DaveB

Hi Dave,
I don't have an actual date, but almost the contrary I think. Before the advent of fouling bars / treadles / track circuits (and not everywhere had such things even latterly) it was all too easy for a signalman to forget a loco sitting at the buffers whilst the crew had a brew and gawped at the girls. Better to have it out by the Starters where it is less easily to overlooked!

Well, that is what I was told! Equally, if the train loco was a Bulleid Pacific trying to get away from Waterloo without using sand, the M7 at the back was the only power available ...


John: not using Templot I see - hmm that makes it quite difficult ... Beware short lengths of unnexpectedly tight curvature - especially by the toes of the switches - everyone who has tried building a curved layout using printed templates and a pair of scissors has fallen down that manhole ...

Best Wishes,
Howard

Proton
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Re: Question Re MPD Track Plan

Postby Proton » Fri Jan 14, 2022 8:39 pm

It is certainly important to avoid kinks but having made well over 100 turnouts in both brook smith and flat bottom copperclad I take the approach, recommended in the early digests of the P4 Soc, that the templates are a guide only, gauges are essential for the actual assembly, so going with that approach, even when a template does have a kink, I always ensure the assembled unit flows smoothly, tweaking the track to achieve this.

J


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