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3rd radius curve geometry


Clement Matchett

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If you look at the Chadwick Model Railway review of The Eastener set on YouTube, you will see that Charlie confirms what I had already discovered for myself in my Scotsman set, that twelve 3rd radius curves don’t form a circle! There is a considerable overlap between the first and twelfth curve!

I suppose this could be an error which applies to only one of the moulds for the sleeper web and that some of us have just been unlucky, but I raised my problem with Simon (of Simon’s Shed on YouTube) and he replied that he had the same issue.

I don’t yet know whether the 2nd radius curves are more accurate, but I will shortly discover…mine arrived on Thursday.

Simon suggested that Hornby may have done this deliberately to cope with expansion and contraction, but personally I doubt that.

I suppose I will have to form my ovals with ten curves and some Peco flextrack, and try to cope with the fishplate issue.

Any comments?

Peter

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I don’t know, Fishman. Some of them are pinned down and I would have to unpin them to answer your question. But when I laid out my track plan, I scribed a perpendicular from a point to give me a 180 turn, together with a cross line at 90. And when I had pinned six curves, it was clear that the intended semi-circle was an arc of about 190 degrees. I added a straight, but it was clear that something was wrong.

As I say, Charlie Chadwick has the same issue.

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I wonder if its just the set track ?

I had some R3 purchased separately and they did not exhibit the "camber" the set track had, maybe its related ...

But I will say, I do think the geometry isn't perfect for any of the curves, at least they don't seem to go together as perfectly as one might expect.

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The R3 curves in my Easterner set were all distorted - when sat on a flat surface there was a very obvious gap (1.5-2mm?) between the underside of the middle sleepers and the table.

I wonder if this is part of the same problem?

My track responded quite well to a bit of manipulation and is now acceptably flat.

Just put them together into a circle - not totally perfect but a 360+/-1 degrees polygon...

I want Hornby to succeed but they do need to sort out their quality control.

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I have just checked my 4th radius circle and that sits flat on the floor with the correct diameter. It looks like a circle and not an oval.

There is always play in the joints for set-track so the above check is not rigorous. I have not set the track out on a scribed circle.

I have not looked that closely at the set 3rd-radius curves in my Easterner set. They seemed to sit ok with the oval I set up for testing but this was just loose on a table. I got the coach scraping sound as the train went round if that means anything.

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Sam's Trains has reported an apparent error with the track geometry, first noticed by Charlie at Chadwick Model Railway. The track geometry is correct. It is that a circle requires either 19 TT8016 half curve 3rd radius, or 9 TT8005 Curve 3rd radius and 1 TT8016. It is just that a piece of TT80016 has not been supplied with the set. You get 10 3rd radius track pieces in the set, but you need 9, plus one half-length 3rd radius curve to make a circle, as the picture below shows.

forum_image_63ef84ec22b09.thumb.png.3e1df47981a17f6f520ae012e267cfca.png

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