2nd & 3rd radii vs 3rd & 4th radii ?

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End2end
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2nd & 3rd radii vs 3rd & 4th radii ?

Postby End2end » Wed Sep 13, 2017 11:26 pm

I am stll considering which radii curves I should use on my loop ends. They definatly cannot be 1st radius as I have longer coaches like the Intercity coaches and I want more freedom then 1st radius gives anyway.
But are there downsides to using 2nd as the inner and 3rd as the outer loop? Or would I be better off with 3rd and 4th radii?
I've only heard problems with 1st radius not 2nd.
I will be using Peco setrack curves although I am not sure what thier part numbers are as they produce so many but if 2nd radius will cause no problems the overall layout size can be slightly smaller which would help although not paramount.
And with that said can anyone tell me what size do 2nd, 3rd and 4th radii Peco setrack circles take up and perhaps the part numbers of each radii please?
Thanks
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby luckymucklebackit » Thu Sep 14, 2017 12:37 pm

This is from the antics online website

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AS a rule of thumb, if you can use larger radii - do it! It looks so much better, less overhang on stock etc

Hope this helps

Jim
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby Mountain » Thu Sep 14, 2017 2:57 pm

I won't say not to use 1st radius curves as on the prototype there were many lines one could only use certain locmotives and rolling stock. So if your layout includes an industrial or a dockside scene, one has a good excuse to lay some 1st radius curves, and like the prototype, these would only be negotiated by locomotives and rolling stock which were able to go round tighter curves. The only thing I will say is also within keeping with the prototype, is to glue on a checkrail next to the inside rail of the sharp curves.
There are also cases of passenger lines which have certain restrictions due to sharp curves. For example, when I used to work trains up the Heart of Wales line (Known as the Central Wales line amongst railway staff), if we brought a 142 or a 143 from Llanelli up we would need to swop the passengers from the down train and bring out unit back down as the platform for the HOW line at Shrewsbury had curves too sharp to take the class 142 And 143's, hence (At that time) the Crewe depot staff I was informed did not sign those units as a safeguard. I have to say that on the curve coming out of Swansea towards Cockett tunnel we nearly got stuck a few times with such units with their wheels jammed tight into the check rails. In the days when they used to take 10 coach trains out of Swansea with a class 47, if they were not doing twice the line speed found the bend they would not get round the curve.

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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby End2end » Thu Sep 14, 2017 4:50 pm

1st radius is most definatly out. I want to be able to run any loco anywhere on the layout. :)
But the size of the outer radius will dictate how big the end baseboards need to be to connect to the rear baseboard.
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby Bufferstop » Thu Sep 14, 2017 5:03 pm

The problem with any model railway curves apart from the minimum radius a loco can traverse is accommodating the overhang both at the ends and in the centre, short 4 wheel stock is ok but look at an APT or Pendo on 2nd radius, its snout is way out from the track, or a full length Mk3 coach with its middle hanging out over the ground and the outside rail actually visible along side the coach. This is why the settrack geometry gives such a wide separation of the two tracks. If overhang is likely to be a problem and the curve won't be visible use the same radius for both, you will then get a very wide separation where it is needed. On visible sections and closer spaced tracks finding an excuse for them to separate in the curve might solve a problem, a bridge that needs a pier between the tracks or a stream with low sided girder spans for each track anything that's plausible. I was forced to make the exit track from my "former junction" station tighter than I would have liked, a grounded van body and and a storage yard mask the inner overhang, and an overbridge cuts of the leading end view but the clearances are tight.
The entrance track at the other end of my layout is the curved side of a Streamline short point, and it comes close to the platform ramp. All was ok until I sent down City of Truro, and it did the same as its prototype and hammered the platform edge with its outside cranks. I had to adopt the prototype solution and cut back the platform edge.
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby NedFlanders » Thu Sep 14, 2017 5:27 pm

Apologies from joining in but this topic is very timely for me - I'm wrestling with track plans at the moment as my son asked could we have tunnels and bridges. so my thinking cap is firmly on and I couldn't figure out if I could have curved points crossover from 3rd to 4th radius curves to save on space - looking at the geometry info in Jim's post (thanks Jim), it would appear not - am I correct?

This would appear to put the thought of only having 3Rd and 4th radius curves on the mainline out of the question, which was my goal to allow a Bachmann HO Hogwarts Castle run on either mainline as when we tried it on the trakmat layout we have built it did not like the second radius curves at all.

Thanks for any answers.

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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby Emettman » Thu Sep 14, 2017 5:59 pm

Do you have plans for covering or part-covering the end curves?

If the rearward quarter-circle is 2 & 3, while the front is 3 & 4, that's 2" of saving on overall width,
effectively three inches if the inner line is three pieces of 2 and one of three.

Hillsides, backscenes and buildings are key here, allowing maximum space saving at minimum visual compromise,

Chris
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby End2end » Thu Sep 14, 2017 6:20 pm

Thanks Bufferstop and you raise a good point NedFlanders. I don't know what the Hogwarts class is but it's a long loco so hopefully the track radius that can accomodate it should be able to run anything I'd like possibly. Can someone confirm this?

On the subject of overhang, what is the overhang like with 3rd radius? As I said before I can accomodate 3rd and 4th radii rather then 2nd and 3rd.
Also I may not have made myself clear in my initial post.
The actual measurement I need is the width and depth of space 3rd and 4th radii takes up as the 2 lines show.
setrack.jpg
setrack.jpg (39.74 KiB) Viewed 153 times

I cannot see the actual space measurements on the 2 track diagrams.To make it even more confusing the text of the peco diagram does not mention 4th only 1st 2nd and 3rd. :?
Thanks
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby luckymucklebackit » Fri Sep 15, 2017 8:24 am

Track spacing on Settrack is 2 5/8" (66.675mm) one of the model railway norms, it hasn't changed since Tri-ang Series 3 days (etched in my brain that one, didn't even need to look it up!). The overhang steadily decreases as you increase the radius, it is still noticeable on a 24" radius (flexitrack)curve, but much less so.

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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby Bufferstop » Fri Sep 15, 2017 10:39 am

For smooth running Settrack curved points are best avoided, especially in a crossover formation. The smaller of the two radii has to be tightened to make them fit the geometry. Streamline ones should be used cautiously we are still talking in terms of radii that would never be encountered in the same formation full size. If you find yourself planning a curved junction and propose using Streamline curved points, go the whole hog and do the whole lot in flexitrack, I think you need the smoothest transitions in your curves not the settrack step changes.
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby Mountain » Fri Sep 15, 2017 10:58 pm

Probably the easiest plan for curved points is to buy code 100 streamline points and a length of flexible track (Code 100 has the same rail height as sectional track). Then, use sectional track to draw where the rails should go and form the crossover and cut the flexible track to fit the shortfall between the section track geometry. I hope this makes sense.
(By using the larger radius curved points from the streamline range you can form the crossover with the wider geometry and still fit it all in the space where standard flexible track curves would have been (Hence why the need to draw using standard sectional curves on the layout as a guide)).

Bufferstop. I've always found the sectional geometry spacing between the rails (The 6ft) to look about right. Took a while to work out why. I live in former broad gauge country so our lines are naturally spaced wider apart! (Broad gauge was 7' and later increased to 7'¼" to cope with higher speeds for those puzzling what broad gauge is. While standard gauge was 4'8" and was later increased to 4'8½" to cope with higher line speeds,especially round curves).

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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby End2end » Thu Sep 21, 2017 12:29 pm

End2end wrote:The actual measurement I need is the width and depth of space 3rd and 4th radii takes up as the 2 lines show.
setrack.jpg

If I could just bring this thread back round to my original inquiry. Does anyone know what size baseboard I would need for the 3rd and 4th radii previously posted?
Thanks
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby luckymucklebackit » Thu Sep 21, 2017 4:14 pm

1.244m (4' 1") allowing for 2" between the centre line of the outer track and the edge of the board, you could probably do it in 4ft, which would leave you with 1" each side

Jim
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby End2end » Thu Sep 21, 2017 8:32 pm

How wide would the baseboard need to be to have that 2" safety margin?
I can cross the gap where the end of the curves do not meet the edge of the baseboard with small straight peices I can cut to make the baseboards dismantible.
Thanks
End2end
Last edited by End2end on Thu Sep 21, 2017 9:09 pm, edited 1 time in total.
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Re: 2nd & 3rd radii vs 3rd & 4th radii ?

Postby luckymucklebackit » Thu Sep 21, 2017 9:08 pm

Read the post - I have answered that question
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