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Post by uzairjubilee on Jun 1, 2010 19:15:26 GMT
Hi all. When on a D stock train, how come you can barely feel you are going over a set of points? I know it's a bit of a weird question  |
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Colin
Advisor
My preserved fire engine!
Posts: 11,346
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Post by Colin on Jun 1, 2010 20:07:46 GMT
Well there are points in both directions at Gloucester Road, but in general it seems that points using newer flat bottom rails are much smoother than the older bull head rails.
I'd imagine there are all sorts of technical answers to your question surrounding geometry, gradients, turnout radius, speed, etc, etc; so this could potentially be an interesting thread.....
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Post by uzairjubilee on Jun 1, 2010 21:18:54 GMT
Oh yeah I was talking about the ones where the Circle separates from the District on the WB and where it joins the EB District.
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mrfs42
71E25683904T 172E6538094T
Big Hair Day
Posts: 5,922
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Post by mrfs42 on Jun 1, 2010 21:45:02 GMT
Turnout geometry plays a part, but also the coning and root radius of the wheels. Unfortunately my technical stuff on track is 300 miles away, so I can only give an educated guess; and heel block clearance notwithstanding, I suspect the ride quality through the divergence primarily relies on the fit of the blades and from that the length of switch planing and the style of switch planing.
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Tom
Administrator
Signalfel?
Posts: 4,196 
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Post by Tom on Jun 1, 2010 22:23:07 GMT
If I'm reading the original question correctly, the two sets of points are 254 between South Ken and Gloucester Road WB and 213 approaching Gloucester Rd EB.
Both sets have been renewed in the last three years with long, low profile switches, with a gentle radius suitable for higher speeds. It also helps that the crossing noses themselves are cast single units, rather than built up from a kit of parts. In fact, the whole layout is pre-assembled off site before being installed on the ground.
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Post by londonstuff on Jun 2, 2010 8:46:59 GMT
Tom - is the 'prefab' nature of points that I've only heard about in the last year becoming more common?
I'd have thought that it made much more sense from a time point of view but suppose that it would require a lot of forward planning, measuring, etc. Places such as the Brixton crossover where there is limited time and space would seem ideal.
From your point of view, what are the pros/cons?
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Tom
Administrator
Signalfel?
Posts: 4,196
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Post by Tom on Jun 2, 2010 21:36:21 GMT
It's been going on for a few years now, but has increased a lot in recent times.
Don't forget that points are usually just made up from a kit of parts. You survey, put together your kit of parts on paper, get the Signal Engineer to approve it, then manufacture and pre-fab. The mechanism and suchlike get assembled as part of the pre-fab, as a dry run, then transported to site and assembled for real. I remember watching one of the junction points at North Acton being craned in from the road bridge about eight years or so ago.
As another example, the layout at Ealing Broadway was prefabricated in mid-April, and most of the mechanism was assembled on the track panel before being installed (I saw it connected to the panel, sitting on an engineer's train during the weekend). It does need more time, but not masses, and the pre-planning saves you time in the long run. The biggest downside from my perspective is that the P/Way Engineer wants you to approve the track design very early on if the crossings are to be manufactured ready for the pre-fab dates.
When Brixton crossover was renewed ten years ago, the whole design was built and prefabricated at Lillie Bridge before being loaded onto an Engineer's Train and transported to Brixton. Far, far simpler than trying to assemble it on site!
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