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topic: 1835Adjacent Track Centres
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posted: 18 Feb 2012 18:14

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dessire_luvals
 
 

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Hi Folks,

Can anyone  point me at or offer any guidance as to appropriate measurement for track centres versus radius of a curve?

I saw Martin's little video for proving the overhang of a carriage but don't think I've come across any easy to consume data.

BTW I'm working in EM Gauge with minimum radius on my running lines of about 48".

Thanks

Russell
Last edited on 18 Feb 2012 19:22 by dessire_luvals
posted: 18 Feb 2012 23:38

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Dellboy
 
Aylesford - United Kingdom

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dessire_luvals wrote:
 
Can anyone  point me at or offer any guidance as to appropriate measurement for track centres versus radius of a curve?

I saw Martin's little video for proving the overhang of a carriage but don't think I've come across any easy to consume data.

BTW I'm working in EM Gauge with minimum radius on my running lines of about 48".

Thanks

Russell
Russell

I've taken the liberty of e-mailing you an excel calculation sheet which should answer your needs.

posted: 19 Feb 2012 02:31

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Martin Wynne
 
West Of The Severn - United Kingdom

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dessire_luvals wrote:
Can anyone  point me at or offer any guidance as to appropriate measurement for track centres versus radius of a curve?

edit: Notes removed as now redundant -- see the new dummy vehicle function below.

regards,

Martin.

posted: 19 Feb 2012 12:24

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Ian Allen
 
Milton Keynes - United Kingdom

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Hi, taking your original question, I have purposely set the track centres on a new plan at 90mm in O gauge because of the issues you have highlighted. IIRC the Gauge O Guild standard is 82mm, so I have allowed for any clearance issues. There is one section though where the track centres have been moved out to 100mm for additional clearance due to the curvature(6' 1" minimum)and gradient profile.

Using Martin's formula, and hoping my calculator and I worked this out correctly, track centre increase should be just over 2mm for a scale 6' radius curve. However on the current SR7mm layout there is one section where the track centres are 85mm and BR MkI coaches have been known to "catch" each other when passing. This will be rectified in due course.

Ian
Last edited on 19 Feb 2012 12:26 by Ian Allen
posted: 19 Feb 2012 13:51

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mike47j
 
 

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Using Pythagoras ?

If r is the radius and b the distance between bogies:
Additional overhang at center c = r - sqrt(r*r - b*b/4)

You could just double that for the needed extra and use 40ft for the bogie centers.

Or calculate the extra overhang at the end using the coach length l as = sqrt((r-c)*(r-c) + l*l/4) - r

Mike Johnson

Just checked the Guild manual and it says that a BR Mk1 should need 80mm centers at 1800mm radius, so something is wrong.
Last edited on 19 Feb 2012 14:10 by mike47j
posted: 19 Feb 2012 22:19

from:

dessire_luvals
 
 

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Thanks everyone. I have used Dellboy's spreadsheet which whilst calculating out more than Martin's formula does seem acceptable.

posted: 19 Feb 2012 22:45

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Martin Wynne
 
West Of The Severn - United Kingdom

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mike47j wrote:
Just checked the Guild manual and it says that a BR Mk1 should need 80mm centres at 1800mm radius, so something is wrong.
Hi Mike,

My copy of the Guild Manual says 84.2mm centres at 1800mm radius. :?

edit: updated link for Templot2:

 http://templot.com/companion/index.html?dummy_vehicle_tool.htm

More in this topic:

 topic 1024

regards,

Martin.

posted: 19 Feb 2012 23:50

from:

mike47j
 
 

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I looked at the online version og the G0G manual which is dated June 1993. The table is at the bottom of Page 2.1.5

This table starts with 9' body width, 63mm.
Then add 3mm for overscale coach door handles, wheel/gauge freedom etc.
Then adds extra for the overhang on curves. 5.6mm for the center with 283mmm between bogies, and 8.1mm for the end with a length of 444mm. To give a total of 79.7mm

However, Ian Allen has a problem with 85mm ?

Mike JOhnson

posted: 20 Feb 2012 06:02

from:

Terry Flynn
 
Australia

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I would suggest an easy way to determine track centres is to use the AMRA standards located at http://www.amra.asn.au/standards.htm which will produce a conservative result for UK models.

Unfortunately the older version with the 1:76.2 scale errors in it are still on the web. Hopefully this will be corrected soon.

Using the latest AMRA standard results for the original question of UK prototype, EM gauge 1:76.2 scale using 48" curves, minimum track centre = 55mm.

For the 0 gauge example the AMRA standard for UK prototype, 1:43.5 scale, 1800mm radius, minimum track centre = 99mm.

The AMRA standard makes loading gauge and maximum vehicle length assumptions for each group of prototypes and includes allowances for the above model railway issues.



posted: 20 Feb 2012 07:22

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Dave Summers
 
Urchfont, Devizes - United Kingdom

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Terry Flynn wrote:
For the 0 gauge example the AMRA standard for UK prototype, 1:43.5 scale, 1800mm radius, minimum track centre = 99mm.

The AMRA standard makes loading gauge and maximum vehicle length assumptions for each group of prototypes and includes allowances for the above model railway issues.
It is these 'assumptions' that give rise to the outrageous figure of 99mm. The assumed maximum prototype vehicle length of 22.9m and a maximum prototype width of 3150mm equate to vehicles over 75ft long and 10ft 4in wide. Since no UK-outline rolling stock approaches these dimensions, the Australian generic data only serves to muddy the waters and should IMHO be completely ignored and discounted for all scales.

Dave

posted: 20 Feb 2012 10:22

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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mike47j wrote:
I looked at the online version of the G0G manual which is dated June 1993. The table is at the bottom of Page 2.1.5
Hi Mike,

I was looking at online Data Sheet D2.1.2 "Curve Clearances" dated August 2002:

 http://gauge0guild.com/manual/02_D2_1_2.pdf

Table 2 at the bottom gives minimum spacings for various items of rolling stock on various radii.

The figure given for BR MK1 coaches on 1800mm radius is 84.2mm.

regards,

Martin.

posted: 20 Feb 2012 11:56

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Ian Allen
 
Milton Keynes - United Kingdom

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To clarify matters, I'll try and find the track dimensions paperwork I wrote up last year for the SR7mm Group Plan Y, in which I took track centre measurements and all other measurements too. As I mentioned, there is only one section, about 6 to 8 inches in length which causes us problems. I'm pretty sure from memory the track centres there were 85mm.

If that is correct, and taking the 84.2mm minimum from the GOG data sheets, then there is only 0.8mm leeway with our 85mm. As Mike has pointed out, loose tolerances in wheelsets/bogies will in fact easily negate the minimum spacing. The trouble was ends of coaches on the inside curve catching the overhang of coaches on the outside curve. Only 6 months before it all gets ripped up though ;-)

Ian

posted: 20 Feb 2012 22:29

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Tony W
 
North Notts. - United Kingdom

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Hi Martin.
Here are copies of the spreadsheet I use, worked out from first principles, which uses the same formula as Mike. This produces results very much in agreement with the figures published by the late Derek Genzel in the Scalefour Society digest. In looking at the figures for the EM track at 24" radius giving a throw of 6.67mm, this is similar to the 7.0mm figure for down to 593mm Radius. However this only allows for clearances to fixed structures and this needs to be doubled for track centres as there is end and centre throw to be allowed for for both tracks. I have had to post a screen shot as Excel files are not accepted as a valid file type, so you may need to go to the gallery to read the original text. Hope this works.
Tony.

2151_201728_420000000.png2151_201728_420000000.png

posted: 20 Feb 2012 23:08

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Dellboy
 
Aylesford - United Kingdom

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Tony W wrote:
Hi Martin.
Here are copies of the spreadsheet I use, worked out from first principles, which uses the same formula as Mike. This produces results very much in agreement with the figures published by the late Derek Genzel in the Scalefour Society digest. In looking at the figures for the EM track at 24" radius giving a throw of 6.67mm, this is similar to the 7.0mm figure for down to 593mm Radius. However this only allows for clearances to fixed structures and this needs to be doubled for track centres as there is end and centre throw to be allowed for for both tracks. I have had to post a screen shot as Excel files are not accepted as a valid file type, so you may need to go to the gallery to read the original text. Hope this works.
Tony.

2151_201728_420000000.png2151_201728_420000000.png


The formula I use provides the same result as you quote for end throw but mid throw will not necessarily be the same value, plus you also need to add a passing clearance measurement to provide your track centers. Attached tables illustrate results for EM from using basic trig formula calculated out by Excel.
Attachment: attach_1363_1835_Track_Centres.jpg 476

posted: 20 Feb 2012 23:10

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Martin Wynne
 
West Of The Severn - United Kingdom

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Hi Derek, Ian, Mike, Tony,

Thanks for your feedback.

But as I mentioned, the geometry on circular curves is not the difficult part. :)

The difficult bits are

a. doing the maths for transition curves, slewing zones, and the turnout roads through double junctions;

b. deciding on an acceptable allowance for model discrepancies such as end-play in axle-boxes, off-centre bogies, body-sway, etc., without creating excessive clearance as in the AMRA dimensions;

c. providing a method in Templot for users easily to check if they have allowed adequate clearance. The spacing-ring tool is useful, but only if you know what size to set it.

So in the next TDV update there will be a new feature to place a dummy vehicle on the control template and move it along the track by mouse action. The corner clearance between two vehicles can then be checked visually or by means of the spacing-ring tool.

The controls will be added to the spacing-ring dialog:

2_231502_110000000.png2_231502_110000000.png

I'm still working on this, hopefully some screenshots tomorrow.

regards,

Martin.

posted: 20 Feb 2012 23:33

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Dellboy
 
Aylesford - United Kingdom

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Martin
Awaited with great interest as this is an old chestnut and suffers much from confusing if not misleading advice. The 'dummy' approach sounds promising!

posted: 21 Feb 2012 00:07

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Tony W
 
North Notts. - United Kingdom

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Hi Russell.
"The formula I use provides the same result as you quote for end throw but mid throw will not necessarily be the same value"
Accepted. It depends very much on the item of rolling stock being considered. The calculations assume balanced stock where the bogie centres are set such that the end and centre throws are the same. Much british coaching stock is close to this ideal. The figures correspond closely to the BR standard mk1 coach. Locos and wagons are a different matter, but bogie stock is likely to produce the largest throws. In practice the longest and widest item likely to use a particular route would be used for the calculations.

"plus you also need to add a passing clearance measurement to provide your track centers."

For a given radius in column 2.
Column 1 gives the minimum clearance dimensions from track centre for the distance to fixed line side structures.
Column 3 gives the corresponding track centres with the increase already added in.

Bear in mind that this spreadsheet was created for my own use and I prefer to keep things simple if possible. They do produce a workable set of dimensions.
Tony.

posted: 21 Feb 2012 00:22

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Tony W
 
North Notts. - United Kingdom

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Hi Martin.
I agree. It is an absolute mine field and one I don't blame you for avoiding for so long. Setting any standard is liable to cause problems for someone. For instance someone modelling the Hastings line may not want as wider track spacing as the rest of us. Educating people to use transition curves to allow for the difference between straight and curved track spacing is a whole new can of worms, but is how the real world works. Your approach is probably the most practical and easiest to understand.
Good luck.
Tony.
Last edited on 22 Feb 2012 14:07 by Tony W
posted: 22 Feb 2012 02:39

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Terry Flynn
 
Australia

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Dave Summers wrote:
Terry Flynn wrote:
For the 0 gauge example the AMRA standard for UK prototype, 1:43.5 scale, 1800mm radius, minimum track centre = 99mm.

The AMRA standard makes loading gauge and maximum vehicle length assumptions for each group of prototypes and includes allowances for the above model railway issues.
It is these 'assumptions' that give rise to the outrageous figure of 99mm. The assumed maximum prototype vehicle length of 22.9m and a maximum prototype width of 3150mm equate to vehicles over 75ft long and 10ft 4in wide. Since no UK-outline rolling stock approaches these dimensions, the Australian generic data only serves to muddy the waters and should IMHO be completely ignored and discounted for all scales.

Dave
Harsh words but it appears the 0 gauge guilds solution underestimates over scale model tolerances for curves, as indicated by others here. The solution in the AMRA standards for all scales have been tested, are far from outrageous, and in some cases tighter than typical model railway practice. I note the Sprinter rail cars are 73'8", only 1' 4" shorter than the AMRA standards length assumption, a minor difference. The loading gauge width difference, 1' again is a small difference when scaled down.

The AMRA solution is conservative for UK prototypes using group 3, but if you want to an easy solution without doing the sums, it's a valid choice. It works and you will have no problems with side swiping of any UK rolling stock, and minimal overall visual difference from a tight as possible value.

If you are only modelling UK steam era then the AMRA group 4 loading gauge will be closer to scale, and still provide enough clearance, though I think it may exclude the Great Central Railway.

For straight track minimum distance for 1:43.5 scale,  the AMRA loading gauge group 3 standard track centres = 85mm, AMRA loading gauge group 4 track centres= 82mm, 0 guild track centres= 80mm.

For straight sidings the recommended dimensions for AMRA group 3 are 92mm, AMRA group 4 track centres= 89mm, 0 guild 90mm.

For a radius of 1800mm, 1:43.5 scale, AMRA group 3 = 99mm, AMRA group 4 = 93mm, 0 guild = 80.6mm (Mk 1 coach)

NEM 112 is more conservative compared to the AMRA standards generally giving larger results for the smaller length vehicles and straight track centre distances.




posted: 22 Feb 2012 08:35

from:

Dave Summers
 
Urchfont, Devizes - United Kingdom

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Terry Flynn wrote:
I note the Sprinter rail cars are 73'8", only 1' 4" shorter than the AMRA standards length assumption, a minor difference. The loading gauge width difference, 1' again is a small difference when scaled down.
......snip
For a radius of 1800mm, 1:43.5 scale, AMRA group 3 = 99mm, AMRA group 4 = 93mm, 0 guild = 80.6mm (Mk 1 coach)
I'm sorry, but you cannot jump in and out of prototype and scale to support an argument in favour of a flawed - from a UK perspective - set of standards. The maximum UK loading gauge width is currently approx 9' 3", I believe, but for pre-grouping and early BR days would have been c9' and less again on branch lines and sidings. The 'extra' 1' cannot be arbitrarily discounted as 'a small difference' as it immediately represents an error of 10% in the track spacing.

The UK current prototype track spacing is c2820mm for straight track. This equates to c78mm for 0 Gauge and is rounded up to 80mm for the G0G standard. I quite accept that we are operating our stock with sloppier engineering over much tighter radii than the prototype, but parameters such as bogie centres will have a big influence on the track-centre widening required. This is where the G0G tables are so valuable since they consider actual UK vehicles. Also, on the prototype, the use of e.g. 70' stock in pre-grouping times would have involved route restrictions because of clearance issues.

Even on modelled 6'/1800mm radius curves, there is still a substantial visual difference between track centres spaced at  99mm and 84.6mm (not 80.6!).

I suspect that the clearances quoted for UK-outline stock in the Gauge 0 Guild Manual have stood the test of time and scrutiny by a generation of modellers and will suffice for most of us.

Clearly, the modeller will need to decide what the maximum dimensions of the stock he/she intends to operate are and adjust the track centres accordingly - which is where we came in!

My apologies to non-7mm scale modellers, but the arguments still apply irrespective of your chosen scale.

Dave

posted: 22 Feb 2012 14:06

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Tony W
 
North Notts. - United Kingdom

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Hi Dave.
Not sure where your figure of 2820mm for track centres comes from as 11'2" works out at 3403.6mm which does scale at about 78mm for O scale.
Tony.

posted: 22 Feb 2012 14:15

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Martin Wynne
 
West Of The Severn - United Kingdom

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Tony W wrote:
Not sure where your figure of 2820mm comes from
Vehicle body width 9ft-3in.

Martin.

posted: 22 Feb 2012 16:54

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John Lewis
 
Croydon - United Kingdom

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For what it is worth, the GWR had some coaches that were 70ft long (over headstocks) x 9ft 6¾in wide with 61ft wheelbase.

posted: 22 Feb 2012 17:12

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mike47j
 
 

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That would explain the GOG choice in 2002 to use 67mm width, which comes to 9ft 6.85 in.

Mike Johnson

posted: 22 Feb 2012 22:07

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Dave Summers
 
Urchfont, Devizes - United Kingdom

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John Lewis wrote:
For what it is worth, the GWR had some coaches that were 70ft long (over headstocks) x 9ft 6¾in wide with 61ft wheelbase.
As I said earlier, I suspect that stock of those dimensions would have had restricted route availability, but I wouldn't expect to have to mention that to John! It doesn't invalidate my assertion that the G0G figures are more relevant to UK stock than the Australian info which is based on assumed dimensions which are not appropriate.

posted: 22 Feb 2012 22:12

from:

Dave Summers
 
Urchfont, Devizes - United Kingdom

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Tony W wrote:
Hi Dave.
Not sure where your figure of 2820mm for track centres comes from as 11'2" works out at 3403.6mm which does scale at about 78mm for O scale.
Tony.
I'm not entirely sure either! I've obviously quoted the vehicle body width figure that Martin mentioned. I should have said 3400mm as highlighted in Tony W's message.

Dave

posted: 23 Feb 2012 02:42

from:

Terry Flynn
 
Australia

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Dave Summers wrote:
Terry Flynn wrote:
I note the Sprinter rail cars are 73'8", only 1' 4" shorter than the AMRA standards length assumption, a minor difference. The loading gauge width difference, 1' again is a small difference when scaled down.
......snip
For a radius of 1800mm, 1:43.5 scale, AMRA group 3 = 99mm, AMRA group 4 = 93mm, 0 guild = 80.6mm (Mk 1 coach)
I'm sorry, but you cannot jump in and out of prototype and scale to support an argument in favour of a flawed - from a UK perspective - set of standards. The maximum UK loading gauge width is currently approx 9' 3", I believe, but for pre-grouping and early BR days would have been c9' and less again on branch lines and sidings. The 'extra' 1' cannot be arbitrarily discounted as 'a small difference' as it immediately represents an error of 10% in the track spacing.

The UK current prototype track spacing is c2820mm for straight track. This equates to c78mm for 0 Gauge and is rounded up to 80mm for the G0G standard. I quite accept that we are operating our stock with sloppier engineering over much tighter radii than the prototype, but parameters such as bogie centres will have a big influence on the track-centre widening required. This is where the G0G tables are so valuable since they consider actual UK vehicles. Also, on the prototype, the use of e.g. 70' stock in pre-grouping times would have involved route restrictions because of clearance issues.

Even on modelled 6'/1800mm radius curves, there is still a substantial visual difference between track centres spaced at  99mm and 84.6mm (not 80.6!).

I suspect that the clearances quoted for UK-outline stock in the Gauge 0 Guild Manual have stood the test of time and scrutiny by a generation of modellers and will suffice for most of us.

Clearly, the modeller will need to decide what the maximum dimensions of the stock he/she intends to operate are and adjust the track centres accordingly - which is where we came in!

My apologies to non-7mm scale modellers, but the arguments still apply irrespective of your chosen scale.

Dave
David,

Unfortunately the reality is you cannot scale down the prototype exactly, you need to allow for extra slop that exists in our models.
The calculations done independently by Delboy in a previous post for 1:43.5 scale at  1717mm radius produced a track spacing of 94mm. The AMRA result for 1800mm group 4 is 93mm. The guilds 84.6mm on 1800mm radius curves seems to tight to me. Others here also have pointed out problems using the guild's standard.  Here is the problem with the Guilds standard as I see it. The wheel track clearance for GOG 0 fine scale standard is 1.65mm. Add axle end play of 1mm we get 2.65mm. Thus as a minimum the track centres need to be more than 2.65mm x 2 = 5.3mm wider than scale to maintain scale clearances. Note this dimension is amplified by the skew angle of the carriage to the track so the actual dimension that should be used is larger. If you take this extra slop into account you see the Guilds standard is to tight, as the guild has reduced the scaled down prototype clearance, from 10.5mm to 3mm on curves to improve appearances. Unfortunately the less than scale clearance used by the Guild is not enough to cover the extra slop of +5.3mm. Add the extra slop value to the Guilds value and you end up with 89.9mm for the BR Mk1 carriage and 93.8mm for the sprinters.

My conclusion is the track centre widths of 93mm and 99mm using the AMRA standards loading gauge assumptions (loading gauge 3 or 4) are close enough to the correctly caculated UK loading gauge widths and carriage lengths for practical purposes. A few mm to wide is better than 1mm to narrow.

The corrected AMRA standard is now on the web at http://www.amra.asn.au/standards.htm

Terry Flynn

posted: 23 Feb 2012 22:04

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Dellboy
 
Aylesford - United Kingdom

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Terry
"The calculations done independently by Delboy in a previous post for 1:43.5 scale at 1717mm radius produced a track spacing of 94mm"

????

I don't recall this and it doesn't appear right to me as it results in 12.75mm passing clearance for a 445mm stock length which seems excessive.
Is my grey matter fading faster than I thought ?

posted: 23 Feb 2012 22:56

from:

Tony W
 
North Notts. - United Kingdom

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Dellboy wrote:
Terry
"The calculations done independently by Delboy in a previous post for 1:43.5 scale at 1717mm radius produced a track spacing of 94mm"

????

I don't recall this and it doesn't appear right to me as it results in 12.75mm passing clearance for a 445mm stock length which seems excessive.
Is my grey matter fading faster than I thought ?
No it isn't, Terry is I think refering to my spreadsheet which you copied in your reply to me.
I did say that it was done for my own use and the 94mm track spacing in fact applies between 1717mm radius down to 1525mm radius, there is a footnote to this effect on the spreadsheet, but it is easily overlooked.
Tony.
Last edited on 23 Feb 2012 22:57 by Tony W
posted: 24 Feb 2012 02:06

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Terry Flynn
 
Australia

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Dellboy wrote:
Terry
"The calculations done independently by Delboy in a previous post for 1:43.5 scale at 1717mm radius produced a track spacing of 94mm"

????

I don't recall this and it doesn't appear right to me as it results in 12.75mm passing clearance for a 445mm stock length which seems excessive.
Is my grey matter fading faster than I thought ?
Sorry Delboy

I got the author of the spread sheet in my message above wrong. It was Tony W's spreadsheets values I was referring to. I note your alternative values and notice your table was for 1:76 scale values, and the clearance you used of 3.11mm, which was less than 1 scale foot. The AMRA standard used a clearance of 1'6" for its calculations from the widest part of the carriages. UK minimum clearance is 1' from the widest part of the carriages. To put this in perspective, The AMRA clearance assumption is 2mm in 1:76.2 scale and 4mm in 43.5 scale wider for UK prototypes. It depends on how much slop you expect built in to your models, but for 1:76 scale models the AMRA standard assumed 3mm loss of clearance, which still results in an under scale clearance on curves for the carriage length and widths used. Yes the end result using the AMRA standard is larger than the minimum possible, but when you design a general clearance standard, it has to cover the worst possible cases. Most RTR locomotives have excessive axle end play and it's model steam locomotives that often have the most end swing, not passenger carriages. Some models will be slightly over loading gauge, this also needs to be considered.

On my old H0 NSWGR layout I used the formula the NSWGR used. For 900mm radius curves it gave an answer of 47mm for track spacing. I used this and noticed 99% of the time everything was OK, but occasionally I would hear the longest carriages just hitting one of my steam locomotives. It did not cause a derailment and I did not notice any damage. One of my personal experiences of what happens when you scale down the prototype without considering model tolerances.

Terry Flynn.

posted: 24 Feb 2012 23:27

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Martin Wynne
 
West Of The Severn - United Kingdom

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I wrote:
hopefully some screenshots tomorrow.
That took a bit longer than expected, but it has worked out quite well. :)

Many thanks to Russell for starting this topic. :thumb:

The new dummy vehicle function is analogous to the existing spacing-ring function, and will often be used at the same time, so I have combined them on the same dialog:

2_231502_110000000.png2_231502_110000000.png


A dummy vehicle can be rolled along the control template alignment, and copies of it can be left at various locations as required. This allows clearances to be checked:

2_241739_180000001.png2_241739_180000001.png
  

2_241739_150000000.png2_241739_150000000.png


2_241739_190000002.png2_241739_190000002.png

The above screenshots show 7mm/ft scale vehicles on 1800mm radius (inner track), with 87mm spacing to 1887mm radius for the outer track.

The solid outline shows the actual vehicle body dimensions. The dashed lines show a clearance envelope along both sides. The centre of the vehicle is also marked for convenience.

The default sizes used are:

body length:  65ft (780")
body width: 9ft-3in (111")
bogie centres: 47ft (564")

which are typical of the larger UK vehicles.

The default side clearance is 6" on each side.

These dimensions can be changed to whatever you want by clicking the dimensions... button. Your vehicle dimensions are saved in the program preferences between sessions. 

6" clearance means that there is more than 1ft between the bodies in the above screenshot, i.e. more than 7mm clear on the models.

In addition to double-track curve clearances, this function will be useful for checking clearances for platform gaps, clearing points in loops and sidings, and clearances for lineside features such as signal posts and bridge parapets.

The curving radius in the control template can be adjusted with the dummy vehicle present, until the desired clearance is obtained. The dummy vehicle remains in position on the control template as it is moved or adjusted in the usual way. However, the copies are not linked to any template and are simply a record on the workpad of past locations of the dummy vehicle. They remain unchanged if the underlying templates are moved or deleted. You can make up to 32 copies.

Like the spacing-rings, this function works as a design aid only on the workpad. The dummy vehicles are not on the printed templates or exported to image files, and not included in .box files.

(The calculations assume that the bogie pin is on the track centre-line. This is not strictly true, especially for long 6-wheel bogies on sharp model curves, but is a close enough approximation for practical purposes bearing in mind all the other unpredictable variables in the models. If a more accurate result is needed, the versine on the bogie wheelbase should be calculated, and the running radius adjusted accordingly.)

This will be in the next TDV update. :)

regards,

Martin.

posted: 25 Feb 2012 02:06

from:

Ian Allen
 
Milton Keynes - United Kingdom

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Martin,

Brilliant, can't wait to try this out :-)

Going back to Terry's post, it would seem my choice of 90mm track cntres is justified from the calculations he has made highlighting 89.9mm for a BR MkI coach.

Happy Tracking everyone.

Ian

posted: 25 Feb 2012 14:04

from:

Tony W
 
North Notts. - United Kingdom

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Hi Terry.
You said "Most RTR locomotives have excessive axle end play and it's model steam locomotives that often have the most end swing, not passenger carriages"
This is a fair point, after working with P4 standards for many years, I had forgotten just how much end throw RTR model 4-4-0 and 0-4-4 locos can have.
Tony.
Last edited on 27 Feb 2012 11:14 by Tony W
posted: 25 Feb 2012 14:06

from:

Tony W
 
North Notts. - United Kingdom

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Hi Martin.
Yes, I like that a lot, well done. Like Ian, I will be very interested to give it a go.
Tony.
Last edited on 25 Feb 2012 14:07 by Tony W
posted: 26 Feb 2012 22:41

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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I have added a mouse action to adjust the clearance markers on the dummy vehicle. This makes it possible to measure the clearance between rolling stock and fixed objects:

2_261727_340000002.png2_261727_340000002.png

(To get a proper result this measurement should of course be made at the vehicle centre-marker.)

This mouse action can also be used to measure the centre axle sideplay needed on 6-wheel vehicles at different radii. Set the body length to match the wheelbase. Set the body width to match the track gauge. The clearance marker can then be adjusted by mouse action to align with the outer rail. Note that the result is shown in prototype inches (I will change this to show also in model mm):

2_261727_310000001.png2_261727_310000001.png


2_261727_310000000.png2_261727_310000000.png


regards,

Martin.


posted: 27 Feb 2012 06:28

from:

PaulTownsend
 
 

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In this excellent new feature do the settable dimensions include an allowance for axle slop, which will vary from say OO to P4, or have you used a preset figure, if so is it defined?

posted: 27 Feb 2012 08:30

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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PaulTownsend wrote:
In this excellent new feature do the settable dimensions include an allowance for axle slop, which will vary from say OO to P4, or have you used a preset figure, if so is it defined?
Hi Paul,

I can't include an allowance for axle slop, wheel/gauge freedom, body sway, wheels offset on axles, bogie pin not central, and no doubt a dozen other variables, because I have no idea what figures would be typical. :( There is no doubt a very wide variation in these dimensions on different models and layouts, even for the same scale/gauge.

What you can do is set the clearance envelope to allow for the likely cumulative effect on your own models. The default is set to show 6" (full-size) clearance markers per body side, which is a figure off the top of my head, but it looks reasonable on the screen.

You can change this to whatever you want, or alternatively adjust it by mouse action to take measurements of available clearance. If you want to measure the clearance free of the above allowances, you could add them to the body width dimension which you set.

Where you have vehicles passing on double curved tracks, it is likely that these discrepancies will affect both vehicles similarly, so that the effect of them may not be too significant -- i.e. both vehicles will be thrown towards the outside of the curve by the same amount, and the nominal clearance between them will be preserved. 

All the figures are currently in full-size prototype inches so that they can apply to any scale, but I will add some model conversions in the display for convenience.

regards,

Martin.

posted: 27 Feb 2012 09:21

from:

Dave Summers
 
Urchfont, Devizes - United Kingdom

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Martin Wynne wrote:
Where you have vehicles passing on double curved tracks, it is likely that these discrepancies will affect both vehicles similarly, so that the effect of them may not be too significant -- i.e. both vehicles will be thrown towards the outside of the curve by the same amount, and the nominal clearance between them will be preserved.
On the prototype, perhaps, with it's great mass accelerating outwards on curves but I suspect that, on our models, it is the pulling force towards the inner rail by the coupled loco and vehicles that will pull the vehicles towards the centre of the curve. However, since that is likely to affect both curved tracks, your argument still applies - unless the inner track has a propelling movement!

Cheers

Dave

posted: 28 Feb 2012 08:35

from:

Jerry
 
Mansfield, Notts - United Kingdom

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I have just looked at my copy of  'Track Topics' Pub Great Western Railway 3rd edition 1939. W. G Chapman.   (I have attempted to follow the author's spelling and punctuation where possible.)

Under  talk 18 'The Load Gauge and Exceptional Loads' p 237 ff which gaily states 'full width  9ft. 8 in., and this latter dimension is greater than that of any other railway in Great Britain'.
It goes on to say 'the extreme width is only available between 4 ft. 3 in. and 9 ft. 10 in.above rail level.

Then it says that 'the load gauge is limited to loads not exceeding 40 feet, and with loads of greater length the width permissible is reduced.'.
I summarise - >40 - 50 ft  max 9 feet,
>50 - 60 ft, max 5ft
>60ft considered "exceptional" only carried by special authority in each case.

BUT ' "What about the G. W. R. 70-feet coaches themselves?".' Then 'These 70-feet coaches, I may tell you, are subject to many limitations in running.'
The GWR ran trial trips with typical coaches; the results of which were considered conclusive.

The book has a diagram (p241) illustrating the situation on a curve given in plan view -
6'6" between adjacent tracks,
9'6" coach 73'10" overall length, 55ft wheelhouse (distance between bogie centres ?) on outer track, and
9'0" coach 74' 0" overall length, 51' 0" wheelhouse on inner track. It also shows this coach at 9' 4" over handles.

You can see that the old railway was conscious of the fact that the overhang of the shorter coach, with shorter distance between bogie swivel points had been taken into account. 5 minutes with a ruler and calculation of the 2 chord lengths showed the correctness of this approach.

I hope this helps other GWR modellers. (if there are any :shock:.)

Jerry

posted: 28 Feb 2012 13:50

from:

John Lewis
 
Croydon - United Kingdom

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> I hope this helps other GWR modellers. (if there are any .)


Thanks Gerry,

I do have a number of GWR 70ft coach kits, including three that are a scale 9ft 6in wide ......:D

posted: 29 Feb 2012 19:41

from:

Phil O
 
Plymouth - United Kingdom

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Hi
John Lewis wrote:
> I hope this helps other GWR modellers. (if there are any .)


Thanks Gerry,

I do have a number of GWR 70ft coach kits, including three that are a scale 9ft 6in wide ......:D
I have a dozen or so plus a few more kits to add to the collection. Only one built a steam rail motor.

Cheers Phil

posted: 6 Mar 2012 07:34

from:

Raymond
 
Bexhill-on-sea - United Kingdom

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Martin Wynne wrote:
I wrote:
hopefully some screenshots tomorrow.
That took a bit longer than expected, but it has worked out quite well. :)

Many thanks to Russell for starting this topic. :thumb:

The new dummy vehicle function is analogous to the existing spacing-ring function, and will often be used at the same time, so I have combined them on the same dialog:

A dummy vehicle can be rolled along the control template alignment, and copies of it can be left at various locations as required. This allows clearances to be checked:


 

Having spent a good deal of the weekend using this new function I have to congratulate Martin on his brilliant idea.  It took me less than half an hour to discover that the clearances in my fiddle yard were insufficient for what I wanted to achieve.  Result, complete re-draw, much easier (and cheaper) than fining out the hard way when it's built.  Next job is to check the rest of the payout and prove it will hold the vehicles I want and clear obstructions.

Thank you Martin, a most useful tool.

Regards  Raymond

 

posted: 29 Dec 2013 03:27

from:

Murryb
 
Temuka - New Zealand

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Having just finished my layout design thought I would check clearances so needed to read instructions and ploughed through above postings. The GWR took out the spider bridge at Crewe with one of their coaches, if I remember correctly it was the door handle on the Guards ogee, this particular type of coach was banned after this. Checks on other vehicles found some only cleared by 2"

Murry

posted: 29 Dec 2013 09:17

from:

Murryb
 
Temuka - New Zealand

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Checked all clearances seems ok. My radius are 1722,1830 80mm apart
Brilliant Tool now have to work out how to post plan for comments. Hope you all have had a good Christmas and haven't been flooded
Murry



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