P4 Track Co Standard and Gauge Widened Bases

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Andy G
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P4 Track Co Standard and Gauge Widened Bases

Postby Andy G » Wed Mar 04, 2009 10:54 pm

With reference to the P4 Track Co trackbases (Fast Track) can anybody answer me a few, probably basic, questions:
1. At what radius do you need to change to the gauge widened track bases?
2. How do you transition between the two?
3. What is the gauge of the widened bases?
4. Does anybody have any long term experience of these in layout use?

Reason for asking is that we are likely to be undertaking a considerable amount of track replacement later in the year and P4Track Co bases are likely to be prime candidates.

Andy G
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Russ Elliott
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Russ Elliott » Thu Mar 05, 2009 1:52 pm

Andy - there are no absolutes in the gauge-widening game. If you've only got 2-axled things, you won't need any widening. I would suggest your approach to the problem should be based on what your loco wheelbases, and their inner-axle sideplay allowances, will dictate or need. Useful information about this is given by the normal versine formula:

v = (c x c)/8r

In terms of the limiting case of a centre axle displacement on the rails:

v = TG - BB - 2EF

Don't forget that the versine amount represents only half the total inner-axle sideplay dimension.

Regarding the transition between ungauged-widened and gauge-widened track, I wasn't aware that Exactoscale did gauge-widened FastTrack flexible bases - is this new?

davebooth

Re: P4 Track Co Standard and Gauge Widened Bases

Postby davebooth » Thu Mar 05, 2009 2:13 pm

Andy G wrote:With reference to the P4 Track Co trackbases (Fast Track) can anybody answer me a few, probably basic, questions:
1. At what radius do you need to change to the gauge widened track bases?
2. How do you transition between the two?
3. What is the gauge of the widened bases?
4. Does anybody have any long term experience of these in layout use?

Reason for asking is that we are likely to be undertaking a considerable amount of track replacement later in the year and P4Track Co bases are likely to be prime candidates.

Andy G


Have a look at http://www.mmrs.co.uk/technical/Langan%20articles.htm Andy! :o
This is actually about calculating required side play for a given wheelbase but it also gives some guidance as to how much gauge widening will be helpfully. Of course with gauge widening one must stay within track gauge tolerances.

Andy G
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Andy G » Thu Mar 05, 2009 2:50 pm

Dave,
I know about John's article - it was me who scanned it for the web site and I've just used it for calculating the sideplay on the Ivatt I'm building. However, P4 Track advertise standard and gauge widened bases but don't give any further information such as how wide the gauge widening is or how you are supposed to switch from a gauge of 18.83 to one of 19mm for example. I'm well aware that the amount of widening would normally vary depending on the tightness of the curve but here we seem to be being presented with two fixed gauges. It probably wouldn't matter to most of us as the existing gauge narrowed track has proved satisfactory for most stock, but there's some awkward so and so who insists on building to S4 standards ;) .

Andy
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Andy G
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Andy G » Thu Mar 05, 2009 2:53 pm

Russ Elliott wrote:Regarding the transition between ungauged-widened and gauge-widened track, I wasn't aware that Exactoscale did gauge-widened FastTrack flexible bases - is this new?

Russ, it's not new as I remember sending an email to Exactoscale a few years ago asking how you go between the two but never got a response, hence the question now.
The items are:
4FT 101A P4 FastTrack 18.83mm gauge for BH rail (2 metres)
4FT 102A P4 FastTrack gauge widened for BH rail (2 metres)

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Andy
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Russ Elliott
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Russ Elliott » Thu Mar 05, 2009 3:21 pm

Andy G wrote:The items are:
4FT 101A P4 FastTrack 18.83mm gauge for BH rail (2 metres)
4FT 102A P4 FastTrack gauge widened for BH rail (2 metres)

Ah yes, my mistake, Andy - I couldn't read the Exacto page properly.

I don't know what the design GW is on the widened base - I can only suggest e-mailing Exacto again. I would guess a nominal 0.2mm. The question of how one transitions from one to another is a separate one, and I'm not surprised they haven't answered that!

andrew jukes

Re: P4 Track Co Standard and Gauge Widened Bases

Postby andrew jukes » Thu Mar 05, 2009 10:20 pm

This thread got me to register at last!

FastTrack was designed before my involvement with Exactoscale, but I have used lots of it for 'behind the scenes' track. No running experience yet so my approach, though thought through, has yet to be proved successful. I am intending to run large six- and eight-coupled locomotives with wheels set at a relatively wide back-to-back, so gauge widening is important.

I have several curves in the 1200mm - 1600mm radius range and have used gauge widened FastTrack for all of them. From memory (I'm not at home just now), when I've checked the gauge 'as laid' using the Exactoscale set of four track gauges, the +0.2mm fits but the +0.3mm doesn't - but I'll check again and report what I find. The curves all have traditionally laid out transitions in which the radius is proportional to the distance along the transition, so for example halfway along the transition into a 1200mm radius curve, the radius locally will be around 2400mm. My standard approach has been to regard roughly 2000mm radius as a sensible point to start gauge widening.

My rule in making the switch from standard to gauge widened track bases is to do it at around the 2000mm radius point, always within a track panel and to let the inherent 'give' in the plastic bases cope with the gauge difference. (I use 320mm panels behind the scenes, but for visible track they would more usually be 240mm or, with dummy joints halfway, 480mm). The result is likely to be that the widening is spread over maybe 100mm. In assembling the track, I always do my best to get the rails curved to the exact curvature required (including to the transition alignment) so that the track is otherwise unstressed when laid.

I'll try checking the gauge through one of these changeover points in the next few days.

Andrew

Andy G
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Andy G » Thu Mar 05, 2009 11:40 pm

Andrew,
Thanks for the reply, most informative. We've just been having a meeting to decide what route we want to take with the replacement track and, assuming we get Committee approval, we are looking to go with the plain line bases rather than the Fast Track so hopefully we'll be able to build the requisite gauge widening in as we go with track gauges. The information you gave will, however, be useful when I come to my own layout that if all goes to plan will have a considerable amount outside (subject to experiments!)

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Andy
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grovenor-2685
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby grovenor-2685 » Thu Mar 05, 2009 11:46 pm

This is what the big railway thinks:
New installations
Curve radius, metres. Gauge, mm.
>200 1435
200 - 176 1438
175 - 151 1441
150 - 126 1445
125 - 101 1448
<101 1451

Notes
1. Changes in gauge shall not be steeper than 1:400, ie 3mm per 1200mm nominal (two sleepers)
2. The outside rail shall be considered as the datum for all gauge widening.

Existing installations, 95RBS, 109FB, 113FB 1435mm gauge
(this is the table relevant to pre-1960s layouts)
Curve radius, metres. Gauge, mm.
200 - 140 1441
140 - 110 1447
<110 1454

Same notes.
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Keith
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Rod Cameron
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Rod Cameron » Fri Mar 06, 2009 9:48 am

Duly noted in relation to the DRAG test track thank you! (radii on the four tracks will range between 1725 mm inner and 1875 mm outer, transitioning from straight over a distance of about 600 mm).
Rod

allanferguson
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby allanferguson » Mon Mar 09, 2009 10:57 pm

I just caught up with this thread. I happen to have some exactoscale widened track on the bench, so I measured it. It is 19.05 - 19.06 mm gauge, i.e. about 0.23 mm wide. I need to have curves of around 1050mm on the non scenic ends of the layout, but I model pre BC (Bogie Coaches!) which means generally shorter stock; although 6 wheelers can be the devil to get round bends. I hadn't thought, though, of using it on 2000mm bends, which do occur in a few places elsewhere.
Allan Ferguson

andrew jukes

Re: P4 Track Co Standard and Gauge Widened Bases

Postby andrew jukes » Tue Mar 17, 2009 12:33 pm

I promised to come back with some measurements from my layout - sorry for the delay.

The FastTrack gauge widened track I've laid is all at least +0.2mm. In a few places, it is very close to +0.2mm but generally there is some play with a +0.2mm gauge but a +0.3mm gauge is definitely tight. So I reckon you can think of it as +0.25mm - i.e. much as Allan says. These measurements are on track laid to radii in the range 1220mm to 1600mm.

I should mention again that all this track has been assembled with the rail pre-curved to the correct radius so there is no stress trying to straighten the panel (apart from any resulting from the 1:20 cant of the rails). The measurements cover both old (brown) FastTrack and recent (dark grey) mouldings.

I have also attempted to measure the gauge through a standard gauge to gauge-widened transition. The gauge change is a little more sudden than I hoped. So far as I can judge, it starts widening about 50mm before the changeover point and is fully widened by about 30mm after, so a total transition length of about 80mm. Not sure why it's asymmetric, but it certainly seemed to be. Reassuringly, the standard gauge track took an 18.83mm gauge just nicely.

Andrew

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Re6/6
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Re6/6 » Thu Mar 26, 2009 8:18 am

We are proposing to use on some circuits of the Devon Riviera Area Group (DRAG) test track, the excellent Tillig superelevation strips. Any views out there regarding their use combined with gauge widening, using 'Fast Track'? Would canted standard track on the superelevation strip guide the stock round smoothly enough, without the need for the gauge-widened track?"
It has caused me however, to stop and think whether there is a link between gauge-widening and canting or not.

Tillig super elevation new-track-bedding.jpg

superelevation-1.jpg
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John

andrew jukes

Re: P4 Track Co Standard and Gauge Widened Bases

Postby andrew jukes » Thu Mar 26, 2009 12:21 pm

I think cant and gauge widening should be thought of in quite separate compartments.

Gauge widening is all about coping with the mismatch between vehicles, parts of which are really designed for straight track, and the sharp curves they are often asked to run round. Wheelsets with large diameter wheels, and so a long length of flange alongside the rail, forced (because of being in an inflexible chassis) to run at a slight angle to the track need more room than they would if properly aligned. Additionally, an inflexible chassis with more than two wheelsets needs sideplay or extra slop between the wheelsets and track if it is to fit the curve. Hence the need for gauge widening, simply to deal with these geometrical problems.

Cant on a full size railway is about passenger comfort and track wear. Uncanted curved track will mean passengers feel the full effect of the centrifugal forces resulting from curving and will mean the outer rail has to both take more vertical load that the inner rail and generate the side forces required to make the train move in a curved path. Cant is used to reduce these effects as far as possible, though it is often a compromise as train speeds differ and trains may have to stop on the curve. On a scale model, the laws of physics (and the lack of passengers!) make both effects unimportant and putting scale cant on is likely to introduce new problems. Real railways use up to 150mm of cant (1 in 10 is an better way of thinking of it) and if you put that on a model, long freight trains could get pulled off the inside of the curve too easily.

On a 4mm scale model, some cant looks good but probably the less the better. I have used around 1 in 40 as my maximum but more typically kept to about 1 in 100. I've yet to see if any of this creates problems.

Andrew

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Re6/6
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Re6/6 » Thu Mar 26, 2009 12:56 pm

Thank you for your interesting reply Andrew. More food for thought! Over to Rod and Tim of our p/way dept!
ATM we're having problems with our current test track regarding the gauge widened curves going too wide and some swb wagons dropping inside. (not Exacto)

Rod Cameron wrote:Duly noted in relation to the DRAG test track thank you! (radii on the four tracks will range between 1725 mm inner and 1875 mm outer, transitioning from straight over a distance of about 600 mm).

Any recommendations, given the above radii? :?
John

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Rod Cameron
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Rod Cameron » Thu Mar 26, 2009 1:13 pm

Thanks Andrew, that pretty much corresponds to my offline conversation with John (Re6/6) yesterday.

The DRAG track will have four circuits with curves between 1725 and 1875 mm radius, transition in from the straights over 600 mm or so. This lies within the radius that you applied gauge-widening to. Relating to Keith's numbers on the real railway, 1800 mm radius in 4 mm equates to 137 m, for which gauge widening of 10 mm would apply for new track, or a scale 0.13 mm.

(John, since this is for a test track, and we have eight curves to play with, what about having all four combinations - with or without widening, and with or without cant, so that the effects can be observed for all cases?).
Rod

Andy G
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Re: P4 Track Co Standard and Gauge Widened Bases

Postby Andy G » Thu Mar 26, 2009 8:18 pm

I know it's narrow gauge but I don't think that will have any affect on it but when I was working on the Welsh Highland I am fairly certain the tight curves had cant and gauge widening applied to them.

Andy
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andrew jukes

Re: P4 Track Co Standard and Gauge Widened Bases

Postby andrew jukes » Fri Mar 27, 2009 6:13 pm

Andy G wrote:I know it's narrow gauge but I don't think that will have any affect on it but when I was working on the Welsh Highland I am fairly certain the tight curves had cant and gauge widening applied to them.


My point was that you've got to think of them separately, not that you can't have both.

If you want to run, say, Virgin Voyagers at high speed on sharpish curves, then some cant (though a lot less than 150mm scaled) but no gauge widening would be logical. If you have a tightly curved station approach and want to run large-wheeled six- or eight-coupled locos, then maximum gauge widening and no cant would make sense. Put the large wheeled locos on the high speed curves and you need the gauge widening and (mainly for appearance) might want to have some cant.

The point about cant not scaling is important (and covered in the Genzel sections of the Digest). Because mass and the forces involved in curving do not vary directly in proportion to the scale, the amount of cant needed for equilibrium curving (when there is no side force on the rails) is much less than you would expect. In 4mm scale, instead of being 1/76th of full size, it is 1/76 squared, or 0.00017 x full size. So 150mm (the max. allowable in full size) becomes 0.026mm on a model if everything else is to scale - not exactly noticeable!

But of course, we want to run at express speeds on curves that are maybe a tenth or twentieth of scale radius. As curving forces are inversely proportional to radius, this makes cant in the range 1/100 to 1/40 (raising the outer rail by 0.2 - 0.5mm) appropriate. Remember, though, that even this will be unhelpful for slow trains which will be hard against the inner rail and a possible problem for long slow freights which might get pulled off the inside of the curve.

Andrew


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