# Minimum radius for long trains?

• posted

I'm trying to fit the maximum length of double track main line into a tailchaser layout set diagonally across a 12ft square loft space. The largest storage sidings at the back will accomodate the sort of train I'd like to run, i.e. a locomotive and 9 or 10 BR Mk 1s. What is a realistic minimum radius for the 180 degree turns to the scenic part? These curves will be horizontal. Thanks, Robert

• posted

If you see the train traversing the curve from the inside, 24" radius looks OK, just. From outside the curve the bend in the train looks sharper, so you need at least 36" IMO. If you don't see the trains at all, then reliable operation suggests a radius of 24".

If you want to see the trains rounding the curve, go with the largest radius that will fit your space, allowing about 3" from the centre line of the outside track to any nearby obstructions (walls and such). Allow

4" from track centre line to edge of layout, to avoid the deleterious effects of plunges to the floor. Also, make the layout scenic edge a half inch or so higher than the track level on outside edges, this will catch any derailing trains. If you can't spare that much space, fasten a fence of 2"-3" high clear acrylic along the layout edge.

A quick calculation shows that you would have close to 8ft of straight away between 36" curves in diagonally opposite corners, and about 11ft if you use 24" radius curves. 48" radius end curves will yield about 5ft of straight away. Keep in mind that your normal angle of view is unlikely to let you see more than about 3 feet of train at a time, so that even a straight away shorter than the length of the train may not look as bad as it sounds.

NB that you will likely need some access to the centre of your layout if, as the limit of safe and comfortable reach is about 24" from the layout's edge. Keep in mind that your back will thank you if you don't have to duck under the table to get there.

Footnote: I suggest that you think hard about the scenic theme of your layout _first_: A junction? A section of mainline in the northwest (Settle & Carlisle style?) Mainlines in the Midlands? Etc. Then plan a series of scenes, each about 6ft to 8 ft long, place them where you and your friends can get a good look at the trains running through them, and connect them with mostly hidden track, much of which can be at the minimum radius for reliable operation (ie 24"). Your staging yard (storage sidings) could be developed to look like a marshalling yard, ie, it could be another scenic focal point. I think you could have four good looking scenes, including the staging yard. Don't forget aisle space: it's difficult moving around a layout with less than 30" wide aisles, and if you expect people to pass each other, you need at least

36" wide aisles.

Have fun!

• posted

My suggestion would be to increase the radius as far as possible - somewhere around 4 foot in your case. Alternatively, you could go up to 5 foot and tighten down to 3 foot in your fiddle yard.

Graham Plowman

• posted

Thanks for the very comprehensive reply! The curves will be out of view, although they may begin to tighten gently in the scenic section to add interest and ease the transition, so I'm just after the smallest reliable radius. My coaching stock is fitted with Keen close couplings. 24" sounds fine. The theme is a section of main line in the Northwest, circa 1960-2. Possibilities include the North Wales coast line to Holyhead that I remember very well, although I don't want to model a major station, or, as you suggest, the Settle & Carlisle. The latter has the advantage that the scenery could be quite simple moorland and a couple of passing loops, together with box would add some operational interest as goods trains wait for expresses to pass. As you may have guessed my main interest is in watching the trains go by, so I'm not bothered about shunting sidings, but a large MPD would be nice to display my Pacifics. The snag then is explaining what such a facility is doing out in the wilds, (I'm not going to attempt a chopped down Tebay!) Time to start the detailed drawings. Thanks again, Robert

• posted

Thanks Graham. All of the curves will be out of view, the scenic breaks cutting across the tracks before the curves really begin to tighten, so I'm only concerned about reliable operation. Do you think 24" is too small? Thanks, Robert

• posted

Chris Leigh covered this subject in a book many years ago. The trouble with wide radius and transsition curves in a limited space is that they leave you without a decent run of straight track and the trains appear always to be going round in a circle. Better - in his opinion - to have tighter curves and a longer stretch of straight.

(kim)

• posted

ISTR there are some good illustrations of this in one of David Jenkinson's books. "Historical Railway Modelling", I think.

MBQ

• posted

Transition curves are _essential_ for reliable operation, especially if you use close coupling on long cars. See John Armstrong's discussion in his Track Planning for Realistic Operation, based both on geometry and practical testing. A transition curve will cut the side-swing of the car's end in half or less, thus reducing those sideways pressures that cause derailmenats, and pretty well eliminating diaphragm (bellows) lock and buffer lock.

For a 24" curve, a transition curve needs about 1/2" in additional width, and the transition curve itself will use about 8" of the tangent. A small price to pay for reliable operation IMO.

One of the benefits of using flex track ius that it forms a natural transition curve, unlike sectional track, but it helps to allow for this when laying out the centre lines.

Bonus 1: Armstrong points out that with transition curves you can tighten up the main radius, as the critical area is the transition from straight to curve, not the curve itself. In Robert's case, that would mean 22" or less, rather than 24", which could mean an extra storage yard track, etc. Testing will show what minimum radius his equipment can handle reliably.

Bonus 2: The train looks much, much better easing into a curve than jerking sideways all of a sudden, as anyone who has seen it will tell you.

Final thought: A train looks much better on a very wide radius curve (8ft or more) than on dead straight track. Since Robert likes to watch trains, I'd advise his considering introducing such purely cosmetic curves. Imagine a station on such a wide radius curve, with the platforms at scale distances from the coaches as they race through at 60 scale mph.... :-)

HTH

• posted

In article , Robert writes

Depends on how free running your stock is. Each item is only "aware" of it's immediate neighbours. It's only when one falls off, that they all fall off.

• posted

But... That's not a real railway. ;-)

• posted

I have only 6' x 8' for my layout, and my Hornby/Bachmann/Lima RTR trains run reliably on curves of 17-22" radius, a combination of flexible and sectional by Hornby, Peco and Atlas. Joints are made with solder or conductive epoxy. I made some careful adjustments to wheel back-to-back dimensions, and replaced plastic rolling stock wheels with metal ones. I use Keen couplers and gangways between coaches and Kadees elsewhere.

Because the latest Atlas flex track has one rail permanently attached to the base, it's easier to maintain even sleeper spacing than with Peco. It's also cheaper - in Canada.

• posted

In message , MartinS writes

That's a bit like Hornby's semi-flexible track.

Since you get what you pay for, does that mean that it's not very good?

• posted

Atlas flex is IMO one of the best available, along with Shinohara. When I used Peco some decades ago, I found the gauge tight (a few thousandths under NMRA minimum), which was OK on the tangents, but tended to bind long wheel base locos on curves. I understand Peco has fixed this problem, in which case I would put it on a par with Atlas. But Peco costs about twice as much as Atlas over here.

The only flex I would rate higher is Micro-Engineering's, which however is more delicate, with near scale size plastic spike/bolt heads holding the rail.

As for even sleeper spacing - that's another one of those bugaboos that scares people unnesessarily. Tie (sleeper) spacing varies a little even on the best built track, and on older, less well-maintained lines, it can vary a lot. Go out and have a look. The Huron Central runs next to the highway about 400 ft from my house. I've walked that track many times: no two tie-spacings are the same; they vary about an inch either way, and sometimes more. They're wooden ties, too, which means they vary in width as well. As for colour and texture - they look nothing like the uniformnly brown or black ties of prefabricated model railway track!

That's why I like the look of Micro-Engineering track: its wooden tie track has those subtle variations in tie spacing, length, width, and texture. A little paint, and it's the most realistic stuff around IMO. OTOH, their concrete tie track has that regimenteded look that you see on the real thing.

HTH

• posted

That may be true for Canada but not for British outline - or at least not my period. British sleepers are (or were) extremely regular in both spacing and appearance. I've seen film of a modern day Canadian train that was close to falling off the track if it went more than about 3mph.

(kim)

• posted

"kim"

Ah, you've seen film of the daily "Budd" car here on Vancouver Island? :-)

Rock and roll at 35mph.

Then again, I've seen video of UK track that is in shocking condition compared to when I was last there in August 1968. Train's running over weed strew tracks, rocking from side to side like they never did back in the GOD.

-- Cheers Roger T.

Home of the Great Eastern Railway

• posted

Um, kim, I recall walking along the tracks near the racecourse in Stratford on Avon in the 1950s (a trespassing bunch, we were), but walking on the track was a chore because you had to vary your stride repeatedly if you wanted to use the sleepers. The spacing _looked_ regular at a distance, but it wasn't. OTOH, the track was smooth as silk.

As for uneven track: that's not a function of tie spacing so much as of bad ballast tamping. A few inches either way in spacing won't cause a problem, but poorly tamped ballast will cause rocking and rolling and worse even if the ties are spaced precisely to the millimetre. And then we have the effect of frost on shallow roadbed and the ballast laid on it... Um, that's enough.

• posted

That was western region, doesn't count. If you had walked the line between Nuneaton and Leamington (LMR) you would have found the distance between sleepers was uniformly that annoying distance which is too far apart to walk on and too close to be able to run. "Railwayman's Lope" I believe they call it?

(kim)

• posted

Them's fight'n words, podner. Draw!

If you had walked the line between

I'll take your word for the precision of the spacing.

• posted

Hi Robert,

I am having the same problem and have concluded that 610 mm is the minimum ( without getting too ridiculous in asthetic terms).

Peter A.

• posted

I've ridden a Budd car between North Vancouver and Whistler. Very twisty track (with heavy freight movements). The grab pole in the toilet comes in very handy!

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.