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Track laying

small elevated track

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Boldminer25/09/2019 08:47:36
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Can any-one advise me on the minimum radius for 5" track. I have just had a plot of land made available to me that is 20 meters x 20 meters and would like to erect a track so as to entertain the local kids here in Phuket. I brought my engines over with me with this in mind, but now I just need a little help to get started. A few locals have seen the engines in steam on rolling roads and were enthralled .For myself I hope to relive the enjoyment I got entertaining the kids back in the UK. The engines are 5 and 31/2"g and I need to know for sure whether this is the exact spacing between the tracks or is there an additional allowance to be included

3404625/09/2019 09:05:14
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I think it is the maximum wheelbase likely to be used, multiplied by a factor of 20.

Bill

Derek Lane25/09/2019 09:52:37
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A a total novice I have been reading books on model engineering and have just read in a book by Martin Evans that a 3 1/2" gauge requires a minimum radius is 30ft it did not give any for the 5" gauge

JasonB25/09/2019 10:04:10
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Here

Ron Laden25/09/2019 10:21:08
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Posted by Derek Lane on 25/09/2019 09:52:37:

A a total novice I have been reading books on model engineering and have just read in a book by Martin Evans that a 3 1/2" gauge requires a minimum radius is 30ft it did not give any for the 5" gauge

Thats sounds a lot to me, I would have thought a 3 1/2" could come down to half that radius as a minimum but maybe not, it does surprise me though.

3404625/09/2019 10:39:49
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Caribou in 3.5 inch gauge , wheelbase 1.25 feet, using figures in Jason's post gives an ideal radius of 25 feet, and a minimum of 15 feet.

Bill

JasonB25/09/2019 10:52:22
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Just looked in Model Engineer's Handbook and that gives a min of 18ft but recommended 40ft for 5"g. 14ft and 30ft for 3.5g.

Also says the min should not be less than 20 x wheelbase

Boldminer26/09/2019 05:16:50
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Thanks to all, I now have a good staring point. Next comes the hard part ( making it ).

Regards Colin

Speedy Builder504/11/2019 07:00:21
1840 forum posts
128 photos

Are there any designs for 5" elevated track, I am looking at making garden track that could be elevated on concrete pillars, but which could be removed and used as portable track. I don't really want to start making concrete spans for track to rest on, so the track needs to be rigid enough to support the locomotive and a few passengers.

In my thoughts, I would use either angle of rectangular section steel, unless I found some second hand stuff.

BobH

duncan webster04/11/2019 09:41:15
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We have 30ft radius curves on 5"g, no trouble even with big locos, but we have gauge widening so it is 128mm on the curves, 127mm on the straights. You also will benefit from super-elevation. Depends how fast you are intending to run, but work out the ideal for running speed then halve it, because you are going to be stationary on it at some time.

The wheelbase * 20 figure should be fixed wheelbase I think, bogies/trucks don't count

Speedy Builder504/11/2019 09:52:59
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128 photos

Thanks Duncan, I was looking to see what sections of rail people used. 1" x 1/4" with tubular/ threaded rod distance pieces seems to be used for track of multiple gauges and 5' centres but would that be stiff enough if the track was just for 5" gauge? Perhaps 5' centres are a bit optimistic?

Could you explain what "Super Elevation" is please.

BobH

Brian Oldford04/11/2019 10:33:27
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Despite many of the previous posts it very much depends on the speed you wish to operate. The fixed wheelbase of the engines in use and how much flange wear you'd find acceptable.

Some relief may be obtained by including a degree of gauge widening on the curves and the raising of the outer rail on curves (super-elevation).

duncan webster04/11/2019 13:20:12
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Super-elevation, raising the outside rail relative to the inside like a banked racetrack (eg Brooklands). This reduces the tendency of the loco to topple over on corners. The centripetal force required to make a mass go in a curve is mass * velocity squared / radius (F1 = M*V^2/R). The ^ sign means 'raised to the power of'. The force acting downwards on the mass is mass* gravity (F2 = M*g). If we add these forces together we get a resultant force Fr = sqrt(F1^2 + F2^2) and the angle of this force from vertical is arcTan(F1/F2). If you tip the track at this angle the passengers will not perceive any side force, like leaning a push bike on a corner. However if you come to a standstill there will be be a tendency to topple inwards, so it seems reasonable to use half this angle, then the perceived out-force when going at speed round the bend is the same as the perceived in-force when stationary.

Speed in metres per second, radius in metres mass in kg, although this actually cancels out. g is 9.81 m/s/s. If you really want to do it in mph and feet we need to introduce all sorts of silly factors.

If a 14st man sat in the middle of your proposed span the track would deflect 20mm, which I suggest is quite a lot, and the stress would be 266 N/mm^2 which is definitely a lot, and we've not allowed for the loco , truck and passengers yet. Here's screen dump of the sums

 

h     25.0 mm  
b     6.0 mm  
second moment of area     7812.5 Mm^4  
section modulus     625.0    
young’s mod     207000.0    
span 60 in 1524.0 mm  
load 98 lb 44.5 kg  
      436.5 N  
           
deflection     19.9 mm  
bending moment     166306.5 Nmm  
stress     266.1 N/mm^2  


Edited By duncan webster on 04/11/2019 13:20:53


Edited By duncan webster on 04/11/2019 13:22:30

Edited By duncan webster on 04/11/2019 13:23:59

Speedy Builder504/11/2019 17:26:31
1840 forum posts
128 photos

Thank you Duncan and Brian for your input. To start off with, the track will be just a straight line with the intention of making a circuit eventually. It would be just for 5" gauge, and in my case a "Speedy". 0-6-0

In Duncan's calculation, the deflection is for a single rail ? and the calculation probably would change by the time 3/8" diameter studding holes had been drilled in the rail for spacers along the neutral axis.

Some of the sections I have seen are 3 or 4 rail to allow for 3.5" and 5" gauges, which would be 'stiffer' than a 2 rail setup.

I guess its back to square one, weight of loco, number of passengers on a section and thus loading at worst case points along the section.

What safety factor should one use in calculations?

Being very lazy, I thought there were some existing tables / drawings about. - The case continues

BobH

What sort of deflection is permissible under maximum load ?

duncan webster04/11/2019 22:36:10
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Calcs have half the weight at mid span on one rail. I've no idea what defection is acceptable, but I feel that 20mm is far too much. It will be more when you allow for loco and truck, but not pro-rata as not all the weight is at the centre.

The yield stress of ordinary flat bar is 275 N/mm^2, I'd not go above half of that in service

If you double the depth you 1/4 the stress and 1/8 the deflection, but 2 flat bars spaced apart don't have all that much torsional rigidity. Our track is supported on 3" channel. Very much overkill, but it's the smallest channel readily available. Ex railway point rodding was good stuff for this application, but is as rare as rocking horse droppings nowadays. Hopefully someone with actual experience of a lighter track construction will chip in

Drilling holes won't make a lot of difference if they are on the centre line (Neutral axis), but it will be a difficult issue to make curves, the distance twixt holes on the outer rail will be greater than the inner..

Edited By duncan webster on 04/11/2019 22:37:18

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