First steps in P4 (not for the purist)

Help and advice for those starting in, or converting to P4 standards. A place to share modelling as a beginner in P4.
PUASHP
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First steps in P4 (not for the purist)

Postby PUASHP » Tue Nov 08, 2022 10:28 pm

Dear All,

Although I have been a Society member for many years I have previously modelled in EM and I have a small exhibition layout in that gauge. For my next layout however I have decided to go P4. The decision was made following a visit to Scaleforum and the interesting article I read recently on the use of EM wheelsets on P4 track.

As a test piece I have a 4’ x 1’ board with one point using a C&L point kit and their latest flexi track. Control is by DCC.

As a quickie I have regauged a Bachmann 74xx on Gibson EM wheels. I have reduced the flange depth and thickness of the wheels and been very careful setting the back to back at 17.4mm. For wagons I chose a selection of my EM wagons both compensated and fixed axleboxes. I have tried Gibson P4 and EM wheelsets, along with Exactoscale. Both Gibson types work fine as long as the back to back is correct, the Exactoscale are the best.

After an evenings testing pushing and pulling stock I am very pleased with the results on all wheelsets, even round the 3’ radius curve. This has given me the encouragement to convert other locos and start planning the layout in earnest as I have a 13’ x 10’ space available.

Paul
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martin goodall
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Re: First steps in P4 (not for the purist)

Postby martin goodall » Wed Nov 09, 2022 11:03 am

I was very pleased to see this thread starting. I have long admired Paul Ash's model-making, especially his scenic modelling (as demonstrated at Expo-EM), and I followed the development of his EM layout Hembourne on RMWeb with considerable interest. It incorporated a host of interesting scenic ideas which worked really well.

I also recall that Paul built a small shunting layout using DCC, and I wonder what conclusions he drew from that experience, and whether this new P4 layout will be DC-controlled (like Hembourne) or DCC?

I was interested to see that (even if only as a temporary expedient) Paul is using EM wheels spaced out to P4, which I have, perhaps somewhat controversially, been doing for some years. The key to success is to ensure that your track is not less than 18.83 mm anywhere on the layout, and that the back-to-back of the wheels is set to the minimum P4 setting – nominally 17.67 mm, but in practice about 17.7 mm. Apart from this, the normal P4 track settings can be used, and there is no need to skim the wheels or do anything else to the wheels or track.

This new thread will be one to watch as Paul’s layout is developed.

PUASHP
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Re: First steps in P4 (not for the purist)

Postby PUASHP » Wed Nov 09, 2022 8:06 pm

Martin,

Thank you for the positive comments. I do like what you are doing with your layout and the town buildings will add a great atmosphere to the finished article.

The new layout will be GWR and will be DCC which is in fact the same as Hembourne.

My plan is to convert enough stock to run the layout in 1936 condition initially then work on my preferred period of 1928. I have some Martin Finney kits of a Bulldog, Stella and Dean Goods waiting to be built and a plan is coming together. When the time comes I’ll set up a separate thread with the plan. I can say the layout will be P4 and a fictional location in Wiltshire.

Paul

Terry Bendall
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Re: First steps in P4 (not for the purist)

Postby Terry Bendall » Thu Nov 10, 2022 8:51 am

PUASHP wrote: For my next layout however I have decided to go P4. The decision was made following a visit to Scaleforum and the interesting article I read recently on the use of EM wheelsets on P4 track.


If we were being pedantic Paul, or even "Trying to Get It All Right" :mrgreen: , by using EM wheels on P4 track means you are not strictly going to P4 :D :D :D

That does not matter. From the small amount you have shown you are doing some nice work and rule number work applies. Enjoy what you are doing and have fun. :thumb

Terry Bendall

PUASHP
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Re: First steps in P4 (not for the purist)

Postby PUASHP » Thu Nov 10, 2022 1:28 pm

Terry,

I’m afraid the decision to use EM wheels on some stock is purely the cost of conversion as I have quite a lot of rolling stock already so the plan is run the layout in a mid/late 1930’s period using the converted stock initially. As I gradually build up true P4 stock this will allow me to model the mid/late 1920’s so I can throw in a couple of ex MSWJR locos and the Stella when I build them.

The photo of the 3 wagons I posted shows two with P4 wheels and one with regauged EM. Unless you look very closely it is not clear which is which and they all run fine. My first point build was not brilliant and it was a bit tight to gauge at one point causing derailment on some of the P4 wheeled stock so I have tuned it and it’s fine now. I feel I have learnt a few things already so I’m happy that the layout should run well when finished and the appearance of the track is better than EM which was the target.

I know it’s early days but I have not found a major difference between my compensated and fixed chassis wagons, and that if it derails it is a track issue probably, assuming the wagon chassis is flat and square. All this gives me confidence moving forward.

Onwards and upwards.

Philip Hall
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Re: First steps in P4 (not for the purist)

Postby Philip Hall » Thu Nov 10, 2022 2:11 pm

Experience with the new layout has shown that decent round wheels and a little bit of play in the bearings gives a vehicle that doesn't derail and doesn't wobble along. In extreme cases (like a long wheelbase van which I did not want to compensate or spring) I have resorted to skimming the back off an Ultrascale EMF wheel which gives me effectively a P4 wheel with a slightly deeper flange. Where I am slightly worried is your use of a back to back of 17.4mm. The minimum b-b in P4 is 17.67, maximum usually 17.75mm and a lesser figure will give problems going through pointwork; there won't be enough room between check and wing rails. Or at least it will be very tight.

Philip

PUASHP
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Re: First steps in P4 (not for the purist)

Postby PUASHP » Thu Nov 10, 2022 3:34 pm

Philip

Loving this thread already as some great tips and really starting to understand what will make a smooth running layout. With the larger flange on EM wheels was concerned about the flange hitting the nose of the frog hence the reduced back to back to avoid this issue which was only really apparent on long wheelbase wagons due to the angle of the wheel against the nose and check rail.

At least it is easy at this stage to change the back to backs on the wagons until it is perfect. I will make some decent back to back gauges to make life a little easier in the future as the L shaped one I have is not brilliant and most of the time I set them with the vernier which is a pain. I also like the idea of skimming the backs of the wheels to reduce flange thickness whilst maintaining more depth than the standard P4 wheel. This will probably sort my back to back issue as I am finding it ultra critical with the EM wheels as expected. I just need to make a mandrel for the wheel so I can then hold them in the collet chuck on the lathe.

This activity has already taught me a lot about point construction and which are the critical dimensions to make it work.

Philip Hall
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Re: First steps in P4 (not for the purist)

Postby Philip Hall » Thu Nov 10, 2022 3:50 pm

If you are just going to take the back off a flange to thin it down, then holding it by the tyre in the three jaw chuck will do. It's not ideal, but you're not going to touch the running surface of the tyre. At the same if you're careful you can take a smidgeon off the flange depth as well.

If we take an Ultrascale EM tyre as an example, the root radius of the tyre/flange is approx 6thou. The P4 root radius is 7.5 thou. That's why the EM flange will just about squeeze through a P4 flangeway. If you turn about 7thou off the back of an EM tyre, you end up with a flange that is very close to a P4 one but slightly deeper. It goes through a P4 flangeway with the same amount of clearance as a proper one.

I must emphasise that in my experience this malarkey is not really necessary, but I employ it in odd circumstances to save me work in adding compensation or whatever. For you to be able to use up existing stocks of EM wheels by modifying them it makes sense. You could also buy one of the Society's form tools for reprofiling.

Philip

PUASHP
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Re: First steps in P4 (not for the purist)

Postby PUASHP » Thu Nov 10, 2022 6:59 pm

Philip

Tried thinning the back of the wheel flange in the collet chucked on the tyre. Wow, really quick and easy to do and sorted all of the issues with the critical back to back and runs beautifully. The increased flange depth will help on the uncompensated wagons as is not really visible at a normal viewing angle.

As I have probably 50 wagons and coaches to do this could be my answer and save a lot of cost, thank you.
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martin goodall
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Re: First steps in P4 (not for the purist)

Postby martin goodall » Thu Nov 10, 2022 7:09 pm

At the risk of repeating myself, it is entirely unnecessary to thin EM wheels to run on P4 track provided that the Back-to-Back of the wheelsets is set at or near the P4 MINIMUM (17.7 mm approx). The original Studiolith BB gauge did give this minimum setting.

I repeat the other point I made. If using EM wheels, the gauge of your track must be not less than 18.83 mm anywhere on the layout. This can be checked with a roller gauge. Where it clicks or jumps (if it does), the track gauge may need to be eased out slightly where this occurs.

And that is all there is to using EM wheels on P4 track (provided those wheels are of comparatively recent manufacture, from Alan Gibson, Ultrascale or Kean Maygib).

For locos with outside cylinders, you might find that clearances behind the slide bars are easier if EMF wheels are used (supplied by Ultrascale to order). These wheels have the EM flange profile but the overall width of the tyre is only 2 mm, the same as P4 wheels.

I would still claim that my layout is 'P4' (despite using EM wheels), because the track is built in all respects to standards that are within the tolerances laid down in the published P4 standards.

Philip mentioned uncompensated wagons. I discovered a long time ago that some slop in the axle boxes (on both axles) entirely obviates the need for compensation or springing of 4-wheel wagons and also bogie wagons and coach bogies, unless the wheelbase of the wagon is more than 50 mm (12' 6") in which case compensation might be desirable, although you might get away with rigid suspension with slop in the axle bearings even in this case. In the case of bogie vehicles, any tendency of the vehicle to wobble can be eliminated by mounting one bogie so that it can pivot from side to side and the other so that it can pivot only fore and aft. It is a crude sort of 3-point suspension for the vehicle as a whole.

I'm afraid this sort of things gets the purists really foaming at the mouth, but they should just be ignored. It is what actually works that matters, and to hell with the theory and high-falutin' notions of technical perfection.

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John Donnelly
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Re: First steps in P4 (not for the purist)

Postby John Donnelly » Thu Nov 10, 2022 8:02 pm

martin goodall wrote:I'm afraid this sort of things gets the purists really foaming at the mouth, but they should just be ignored. It is what actually works that matters, and to hell with the theory and high-falutin' notions of technical perfection.


As per the saying 'I know it works in practice but does it work in theory'...

Philip Hall
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Re: First steps in P4 (not for the purist)

Postby Philip Hall » Thu Nov 10, 2022 11:49 pm

Martin, you've been using EM wheels with much success over many years so I am not going to argue! However, I believe the reason that you can get away with this is that the root radius of an EM wheel (at least Ultrascale) is actually smaller than a P4 wheel, which gives just that extra little bit of clearance through a flangeway. On the odd vehicle, I want the wheels to be as near P4 as possible but with a slightly deeper flange. Hence my method of turning 7 thou off the back off the flange. It works very well as Paul seems to have found. EM profile does work but I think thinning the flange makes it better and I feel happier that way.

I am lucky to have a largish roundy roundy to play with, and standard P4 wheels in rigid chassis run very reliably. During the summer, we had a few gatherings of mainly non railway people who would be pretty unimpressed if things were falling off all the while, but these folk were very complimentary about how smoothly the railway ran compared to the rock and roll of your average 00 trains. In fact at times I was driven to run at some pretty frightening speeds (8 carriages behind a Hornby Schools at a scale 95 mph - and occasionally more!) just for fun and possibly to prove the point. Not just once around but again and again. And just yesterday we were trying to identify a motor problem, I accidentally switched a loop in by mistake and sent a Class 33 hurtling round at about 110 with about 12 short wheelbase wagons in tow, and again, nothing fell off nor did the vehicles wobble. Therefore I know that standard P4 profiles work here and do not need altering.

I only monkey around with other wheels for the fun of it, for the odd long wheelbase vehicle, or when the correct wheel isn't available (like for the Dapol LSWR B4). On that engine I actually reduced the width of the front drivers to 1.7mm for other reasons. Perhaps I should keep quiet about that.

Good luck with your experiments, Paul. Keep us posted with your progress.

Philip

Alan Turner
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Re: First steps in P4 (not for the purist)

Postby Alan Turner » Fri Nov 11, 2022 9:30 am

Remember the so called "Prototype" wheel profile is only one such profile that was published in the 1925 BS. That profile was actually an "average" profile of the various profiles used by a number of railway builders.

At present I believe there are 15 different tread profiles in use on British railways; with some unique to a particular locomotive. And that 15 doesn't include Tram profiles.

So to say that the particular tread profile adopted by the S4/P4 (and Scale 7 as well) is THE profile is not correct and it is only one particular profile and incidently would be wrong if you were modelling a Class 87 Electric, which was one of those locos that had a unique profile.

regards

Alan

davebradwell
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Re: First steps in P4 (not for the purist)

Postby davebradwell » Fri Nov 11, 2022 10:06 am

It's the width over the outside of the wheelset that would cause me grief. Splashers often need widening to get clearance on P4 wheels, even the narrower Exactoscale, never mind the delights of getting the coupling rod to clear a crosshead and slide bars. Perhaps it's easier with GW locos and rtr thin rods. You'd not have to be too fussy about width over tender frames, either, as these are usually very close to the wheels and could be stuck with shallow moulded axleboxes.

If you want to test how well your stock stays on the track, try pushing 30-40 wagons through pointwork. You can get away with a lot with short trains and things have to be pretty bad for stock to come off when pulling.

DaveB

Terry Bendall
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Re: First steps in P4 (not for the purist)

Postby Terry Bendall » Fri Nov 11, 2022 10:20 am

PUASHP wrote: I’m afraid the decision to use EM wheels on some stock is purely the cost of conversion


No need for any apology Paul. :)

PUASHP wrote:I know it’s early days but I have not found a major difference between my compensated and fixed chassis wagons, and that if it derails it is a track issue probably, assuming the wagon chassis is flat and square.


Short wheelbase wagons will usually work perfectly well without compensation as long as , as you say, the chassis is flat and square. If it works carry on, if it doesn't, sort out why not and fix it. :D

Terry Bendall

Yorkshireman

Re: First steps in P4 (not for the purist)

Postby Yorkshireman » Fri Dec 30, 2022 10:27 pm

I’m almost sorry to have stumbled across this thread.
After lockdown gave me time to get back to the many boxes of ‘stuff’ that have steadily multiplied and shifted house with me several times, I rejoined several societies and revisited my daydream layout design.

Now with better workshop facilities, more skills, fewer children and suchlike I thought "it’s time to start building." There is plain track off the shelf, templot to layout the track work, and so much available that I had once supposed I would need to make. Good news?

Well, not quite, because my standards are now so high that my layout, with its 200’ or so of track, turnouts galore, scenic sections, buildings and so on is a lifetime’s work. And I don’t have a lifetime to spend on it. Competing pressures on time still exist, so something has to give, and it has to be the daydream….

Why am I rambling on?

Because I can bring myself to jettisoning the rolling stock, various unbuilt locos and all the rest, but I can’t quite let it go without building at least one loco, and a couple of wagons, and a plank of track that could be a tiny, tiny bit of industry, a loading dock at the back of a warehouse.

But the point is that reading this suddenly makes me realise that I can slip in making a small board between a couple of restoration jobs. Ditto some track panels, and a loco. I have some 16.5mm gauge wagons I can modify enough to make it enjoyable.

Most of all though, something about this thread is inspirational enough to make me think it’s possible less than the remaining lifetime.

So many thanks.

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Paul Willis
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Re: First steps in P4 (not for the purist)

Postby Paul Willis » Mon Jan 09, 2023 8:06 am

Yorkshireman wrote:I’m almost sorry to have stumbled across this thread.
After lockdown gave me time to get back to the many boxes of ‘stuff’ that have steadily multiplied and shifted house with me several times, I rejoined several societies and revisited my daydream layout design.

<snip>

Because I can bring myself to jettisoning the rolling stock, various unbuilt locos and all the rest, but I can’t quite let it go without building at least one loco, and a couple of wagons, and a plank of track that could be a tiny, tiny bit of industry, a loading dock at the back of a warehouse.

But the point is that reading this suddenly makes me realise that I can slip in making a small board between a couple of restoration jobs. Ditto some track panels, and a loco. I have some 16.5mm gauge wagons I can modify enough to make it enjoyable.

Most of all though, something about this thread is inspirational enough to make me think it’s possible less than the remaining lifetime.

So many thanks.


Hi Richard,

And that's an inspiring post in itself. Just making a start is often the most difficult step. What you describe as the first few steps will show what it is capable to do. And from there, who knows...

Do share with us the modelling that you start with, and as you know from reading here, there will always be help at hand.

Very best wishes,
Paul
Beware of Trains - occasional modelling in progress!
www.5522models.co.uk

Yorkshireman

Re: First steps in P4 (not for the purist)

Postby Yorkshireman » Mon Jan 09, 2023 5:37 pm

Thanks Paul

I can see at least 8 months of 'real work' ahead, with next to no unallocated hours for playtime in the workshop.

Mentally consigning my 'dream railway' to the bin is somehow a great relief though, as though a modelling weight has been removed. No need to start with the complexities of portable, elliptical baseboards with 2 levels. No requirement for detailing at least one station and village, plus the countryside side open space where you just watch trains go by. And no need for dozens of items of stock.

In fact, I have some loose rail, and some ancient pcb sleeper material that would make up into, say a 250mm length of track - enough to allow a wagon to sit there, or a break van.

Start small! - I get the message..


R

(and with photo's)


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