Very small radius points

[bertiedog]

In working on an Industrial layout, a limitation on the minimum size and general arrangement is the size of the points, the overall length of Peco RTR even in the smallest sizes is quite a waste of space.

I had decided to make some points from Bullhead rail and C&L parts, and built two conventional length 15 inch radius points.

 

Even then they are very long against the effective radius. I have in the past done 4 inch radius tram track, which ran quite OK, but obviously this is far too tight for an engine and stock when pulling, let alone pushing stock.

 

However I decided to try for a minimum radius point with a straight section through the frog, and see what happens with the stock on what would be about 7 inch radius in the area between the blade tips and the tip of the frog crossing.

 

The blades and rail are not a constant curve, it is transitioned slightly into the tightest part, very gently, and the resultant length of the tightest part is minimised. The check rails are extended as far as possible to ensure guidance for the flanges, and the clearances are kept to normal.

 

The odd thing is that stock rolling across the point runs better than on an equivalent longer section of rail at the same radius. Only one wagon is effectively on the tight section at once and the couplings engage just as well as normal in pulling. With pushing the manoeuvre must be done slowly, dependent on the type of couplings. Three link or most auto fine scale types need the buffers connected with fine wire to prevent locking. I am using the Sayer Chaplin Auto, mentioned in other my other posts.

 

The locos are W4 Pecketts and sail through the points easily. A Dapol Austerity also manages the tight curve quite well, as does a Beattie Well Tank.

 

After the 7 inch was made I shortened a second one to about 6 inch, and it still works fine, as long as the gauge is eased open a bit in the blade section of the point. The frog remains at standard

dimensions and the same angle. The running remains very smooth, but the Austerity does get a bit tight on the curved section and jitters a tiny bit when running light.

 

On the tightest radius generally the running is as normal, the speeds are minimal being an industrial line.

 

The first two were built on PC board to test everything, now both are being re-built with the C&L/Exactoscale chairs and final sleeper positioning, with some PC and brass strengthening parts.

 

If they work as well on the chairs I might even try a bit more with a Y point to see how far it will go.

 

The length savings over standard Peco points are big, about 1/2 size, but the appearance is not too bad with the chairs and bullhead track. The rest of the track is Peco Bullhead and matches the C&L point work quite well.

 

Obviously the points are not for coaches etc, but short bogied stock goes over them quite well, as long as the couplers are bogie pivot mounted, not on the buffer beam.

 

Photos coming of the chaired versions being built. The drawings are made on the computer and scaled to size and printed on A4 paper as templates to work too to ensure the entry and exit are where they should be!

[Dunsignalling]

A mate of mine has built a successful layout in O-16.5 on which some of the curves were laid using an upturned dinner plate as a template. Probably about 5.5 inch radius to the centre-line of the track.

 

Mind you, all his locos are 4-wheelers!

 

John

Edited March 25, 2017 by Dunsignalling

[Nearholmer]

I may not have the figure exactly right, but I think that the smallest British Standard radius for 2ft gauge portable track was 13ft 6in [Edit: it was 13ft 3in, and KB Scale have a data sheet with drawings on their website http://www.kbscale.com/pdf/Track&Turnouts-A5.pdf and it is possible to run a light, short-wheelbase, loco around this, and through points (heavy, longer locos bust the track!), as I well know from watching the railway at our local brickworks years ago.

 

This atrocious curvature also works in model form, and I've built points in 0n14 accordingly.

 

So, gauge-radius ratio of 6.625which suggests that, with very short wheelbase, c109mm ought to work in 00.

 

I think that typical standard gauge wagons might be a problem at such a minimal radius, though, because their wheelbase is probably longer than that of tiny locos. Wagons for horribly tight narrow gauge railways, real and model, have very short wheel-base, and usually have curved head-stocks, as do street tramway cars, which negotiate some insanely light curves.

 

Bertram Heyn is the king of madly-tight points in 45mm gauge, and I notice that his most extreme ones (422mm radius, so a conservative 9.4x gauge) are stub-points http://www.modell-werkstatt.de/weichen-45mm

 

Kevin

 

The engraving below is entitled: "I take your point."

Edited March 25, 2017 by Nearholmer

[Dava]

Ouch! That check rail hurts!

 

Dava

[bertiedog]

It's a Man after he has picked up the first Bullhead 4mm scale Point from Peco! He can't help feeling something is a little wrong........

[bertiedog]

The use of stub operation does not really help out on the radius, it is still the crossing that is troublesome. and the only way is to eliminate it with closing blades, like Wrenn did.

 

When closed all the problems vanish, the point ceases to exist to the wheelsets, no flangeways, no adjustments to narrow the gauge etc, and the limit is just the radius.

 

The problem is that they may look a bit odd, but I will try one in bullhead with plastic chairs to see exactly how odd, and whether it is worthwhile to use.

 

I would guess a radius of 6 inch could be done, and would be reliable for running, it is all down to the buffers and couplings used.

The first section of the blade would be normal in chairs including sliding under the tips, but there would have to be a strip hinge added in the blade to allow the frog to close, a small phosphor bronze strip would work. The two rails each side of the frog could be connected by wire, to move together from open to close in time with the blades.

 

The movement is the same as the width of the flangeway, so quite small compared to Wrenn.

 

The blades and frog would be electrically the same, live frog in effect, and require a microswitch to supply the frog. In theory the blades could pick up power from the outer rails, but it might not be reliable.

 

Anyway worth a prototype to see what it would look like, and how well the chairs can take the various bits with or without extra support  from PC sleepers with soldered rail.

 

Stephen

[Ian Smeeton]

I am sure that I have seen stub points where there was NO frog, as such.

 

A section of rail swivelled, depending on the direction that the points were set.

 

ISTR that the swivelling section of rail was connected to the actual point lever so that there was no problem with conflict.

 

Regards

 

Ian

[bertiedog]

There are indeed frogless single blade points, where the blade it straight, and is moved from contact with one running rail over to the other, pivoting on a position that allows the blade end to line up across where the frog would be. But the geometry of the type is crazy, with the sudden lurch from the straight to the angle to the siding, and these types are confined to mines and such line, where the wagons are man handled or pulled by very small locos.

 

On some systems the whole blade is lifted up and moved to the other extreme loosely, purely a manual operation.

 

Stephen.

[bertiedog]

An example of a single moving blade point, Trams used a more sophisticated version, with a frog, the wheels guided entirely by the flanges in grooved rail.

Stephen

[Junctionmad]

An example of a single moving blade point, Trams used a more sophisticated version, with a frog, the wheels guided entirely by the flanges in grooved rail.

Stephen

The health and safety man must be drunk in the pub !! , probably a nixer job from his day job of rat catching

[Nearholmer]

Mr Smeeton might have seen a type of point used on Welsh slate quarry lines, which had a moving set of stub switch rails, and a pivoting section of rail where the crossing ("frog") would usualy be, both operated by a common lever. I think this type originated in places that used double-flanged wheels ( it certainly occurs on German agricultural railways using double-flanges, as well as in Wales), but I've seen them on single-flange lines, too.

 

K

[Orange Cat]

Is that wagon at around 0.45 out of the Thomas the Tank Engine series? It doesn't look very happy.

The OHLE collection apparatus is rather innovative though.

[bertiedog]

The OHLE collection apparatus is rather innovative though.

I hope that you kept a straight face when you wrote it, leaving out carefully the words like lethal, moronic, suicidal, death trap, loony, and downright dangerous............

[bertiedog]

A trial assembly with C&L chairs shows that about 5.5 inches is the minimum, without a closing frog, as the curved part is short, and the gauge can be increased a bit over the blade section. A Peckett does not look silly on these tight curves if the track approach to the point is not at the same radius, which is just asking for trouble.

 

After all, my main intention is to shorten the points to a minimum, not to fit the point to a similar radius track. It is to allow the track to weave around buildings and features in a realistic way, without wasting valuable layout space on end to end dimensions.

 

The appearance is no worse than Dublo set track points, with a Pacific crossing the point!...indeed the Peckett and 4 wheeled wagons look quite at home, it's the couplings, and buffer lock that is still the overall worry.

 

Stephen

[Joseph_Pestell]

I am wondering what the 1:1 scale minimum was for standard gauge. Some of you may have seen the map of Halifax North Bridge station (on thread of same name) which shows some very small radius points on an industrial branch. I will try to work out from the map what the radius is there.

[Nearholmer]

Bufferlock can be avoided by using a rigid link, possibly a three-link with the links soldered-up solid.

 

Rigid links, transmitting pushing forces through the link, rather than buffers, are what all railways with really tight radii use, both real and model.

 

Next down is to use very wide buffers, of course.

 

K

[Joseph_Pestell]

I am wondering what the 1:1 scale minimum was for standard gauge. Some of you may have seen the map of Halifax North Bridge station (on thread of same name) which shows some very small radius points on an industrial branch. I will try to work out from the map what the radius is there.

 

Looking at the OS map again, I reckon that it would be about 80ft radius.

[bertiedog]

Sounds about the minimum. 80/76 = 1.052 feet, lets say one foot model radius, which is quite large really for 00 models.

Some tramways and interurbans go to a scale size of about 6 inches, but standard gauge track would normally be well over 200ft or 2ft 6 inches minimum.

 

The general appearance of the tight radius point is not too bad at the normal viewing angles etc., and with  partially obscured overgrown track, it does not show, especially if the track approaching it carefully blended into the transition from normal to very tight.

 

The stumbling block in pushing stock not pulling, so wired buffers may become obligatory to stop locking, and no reverse curves, there must be a straight approach of about a wagons wheelbase, before a reversed curve.

 

Stephen.

[John ks]

Stephen

 Just read this topic

 I rally love the pantograph in the movie in post 9

Is it one of those automatic compensating pantographs with A.I. (Artificial Intelligence) & voice activated control

 

John