Radius 1 based layout and locomotive limitations

[johncarter]

Due space limitations and having the track already ive a layout will all radius 1 curves. Ive been hearing about certain locos requiring minimum 2nd radius. Is this down to the wheel Base of the non bogie wheels. Is it mainly a problem with steam locos as diesels are twin bogies.

Thanks

[luckymucklebackit]

Most manufacturers now tell you on the description what the minimum radius is, it is down to a number of things, early coarse scale locomotives and rolling stock were specifically designed to run on 1st radius curves but the desire for more accuracy and better detail means that a lot of stock will not tolerate the tight curves, diesels included. The usual minimum curve for prototype main line locomotives was 6 chains (One chain in 00 gauge scales to roughly 10.5") so around 5ft and that would be at a severe speed restriction. We are asking our locos to go round much tighter curves flat out!!

Jim

[Emettman]

Most modern models have less "play" or "slop" in them than which previously helped with the horrendously sharp curves which previously were "normal" by consensus in practice.

An ancient Triang diesel happy on 10" radius curves, without any modification.



Clearance on outside cylinders, front footsteps, loco ti tender coupling: these have all tightened up in the interest of more realism, but to some degree this has demanded (slightly) more realistic track radii.

All things being equal, a bogie vehicle of moderate can manage tight curves more happily than a long wheelbase 4-wheeler,
Triang bogie flat or "London Brick" wagon vs an Interfrigo, for example.

Thus a Bo-Bo diesel might be expected to do better than any six-coupled steam loco (that isn't old/small)

Other factors can be more critical, however: the bogies on a loco may have restricted play, and the limiting factor may be with the tolerance on the couplings rather than with the loco/vehicle itself.

If tender steam engines are wanted in a limited space with restricted curves, 4-4-0's would seem to be the wheel formation of choice, but with modern versions, the limit may lie (I don't know) with how close the tender can or can't be coupled to the loco.

Back in the day, I loved the little short Hymek: it didn't dwarf the length of train I could put behind it.

Chris

[Bufferstop]

Hornby's retention of the old "large D" coupler on Railroad models helps running on radius 1 and 2 tracks. Whilst the NEM mounted coupler helps by being able to flex to the left or right, but compared to the rigidly mounted three hole types it has introduced vertical play (droop) and issues with not centring. Wide wheel treads help fixed wheelbase locos negotiate tight curves but most 0-6-0s need flangeless or undersized centre wheels, reducing them electrically to 0-4-0s. Bogie rolling stock might be expected to cope better, but the amount of rotation is often limited by the lack of clearance between the over scale flanges and the solebars. Body mounted close coupling systems can also have problems, especially if a reverse curve is encountered. I have one which is unavoidable, two streamline short points back to back, it's not a pretty sight when Bachmann coaches pass over it, amazingly the couplings cope.

[GeraldH]

There are one or two lists on this and other forums of locos that have been reported to run OK on first radius curves. The key thing seems to be avoid reverse curves, i.e. curves going in opposite directions right next to each other. It has also been reported that standard set-track points, although nominally second radius, are slightly kinked and are therefore equivalent to first radius.

I have run around 100 different locos through my first radius curves without problems, though I do some online research before buying any and avoid the largest mainline locos like the P2 or 42xx.

[Dad-1]

One of the key elements to good running around 1st radius curves is very good
track laying, no out of alignment track joins, flat and level base with no twist,
or gradient changes.
You will also be limited to slower speeds and a curve connected directly to a point
can cause problems.

There is little reason as to what will and will not run around those tight 1st radius
curves. I have run the Hornby 2-8-2 72XX without problems, yet my Bachmann
0-6-0 Collett Goods derails.
As a general rule most will ........ but even if say my version of the Webb coal
tank runs on my layout, one you buy may not run on yours. This will be due to
small manufacturing variations as well as the laid track quality. You are more
likely to get away with 0-6-0's and what one may call modern diesels which are
much more forgiving, so back with a question WHAT do you want to run ?

Geoff T

[Bufferstop]

The Collet Goods, and various pannier tanks all have a fairly widely spaced wheelbase and a full set of flanges. By comparison various 0-6-0s from Hornby have either no flanges on the centre driver, or it is undersized with a smaller flange and never contacts the rail. The, originally Dapol, Austerity manages with flanges on all wheels but has a much tighter wheel spacing, as the original design was meant to be able to work on docksides and around military establishments where tight curves abound.

[GeraldH]

... yet my Bachmann 0-6-0 Collett Goods derails...

I've been thinking of getting a Bachmann Collett Goods to replace my Mainline one which runs around first radius without problems. Is it the loco, or tender, that derails on the Bachmann one?

[Dad-1]

Hi Gerald,

This is where generalizations all go wrong.
The right question, it's the Tender that derails on my weathered black BR version. The locomotive has no
trouble, as in fact my trouble free Bachmann GWR green version. I have looked carefully at the problem
and it comes to the design where the tender wheels are cast with stub axles that fit into the axle boxes.
The split axles are joined with a plastic muff. If you reduce the back to back which should allow it to run
O.K then the axle ends drop out of the axle boxes !!
Due to my only 1st radius curves being in the garage layout I simply don't run that loco there. Regardless
of what Bufferstop says my Bachmann 57XX's (3), Jinty, and Hornby (S&DJR) Jinty run reliably with full
size wheels and flanges on all wheels. It really is a "try it and see" which is not a great help to the OP as
the last thing he wants is to buy a nice loco that won't stay on the track !!

This is where one has to be rather careful, same manufacturer, model of the same prototype, one works
fine the other plays up.

Most of the time I'm finding Hornby locos manage (Just) and that includes the Evening Star (Railroad) 9F,
Black 5, 72XX, but I can also run the Bachmann Jubilee and if I recall correctly some of my 2-8-0's.

If the OP has particular locos he fancies, IF I have one I could always try on MY track, but I don't have
everything ..... I also easily forget what I have tried, Something from my Bachmann 2 x Midland 3F & a
4F won't run reliably but which ? I'd have to get back to 'testing'

Geoff T.

[Bufferstop]

As you say Geoff same model same manfufacturer different results. If there is any manufacturing trait then it's with back to back dimensions Hornby tending to be tight Bachmann to be wide, but you can't put down anything specific. I don't know if you know this but many people don't the Triang or Triang Hornby split axle wheel sets were intended not only to have end to end play, but also for the one half axle to move independently on the steel core. Rather than gauge widening on the Radius 1 curves they had a wheelset which narrowed, but to get through the pointwork the checkrails pulled the wheels apart. Hence the need for such deep flanges to avoid the wheels climbing over them.

[Dad-1]

Hi Bufferstop,

It really is something of a nightmare for the beginner, so many different methods and no
real standards.
My money would tend towards Hornby for the benefit of those wide couplings where fitted,
as you say, they help keep stock on the track by giving enough spare lateral movement.

No wonder manufacturers say 2nd radius minimum, very few give trouble on that and they've
covered their backsides !!

Was talking to a local buddy (Just out of hospital) about Milk tanks. Yes you've guessed it
the Dapol wagons keep derailing. The only long term solution there is to think 'Triang' and
file off all traces of flanges from the centre wheel set ...... But pity the beginner !!

Geoff T.

[Bufferstop]

Many years ago I pursuaded a Triang motor bogie complete with twin worms and knurled wheels to negotiate a six inch radius curve of Wrenn flexible track, code 126 IIRC. All it had to carry was a double decker tram body and the noise was deafening, but it went round every time. With rails that size and Triang's back to back the inset track just didn't look convincing. Even the cheapest sets come with R2 curves, time they put a health warning on the boxes of R1s.

[johncarter]

Wow. thanks for all the replies

[Bufferstop]

There's far more to laying track than most people anticipate, reverse curves or 'S's being one problem, I know, I couldn't avoid one, it's immediately at the end of a platform. City of Truro with its outside flying cranks manages it no problem, Rood Ashton Hall bashes its cylinder on the top of the ramp about four times in ten when pulling a train, no trouble at all running solo. I've placed the signal box so that it just obscures the adjacent ends of coaches as they negotiate it, the sight is just too gruesome. At a different spot a train leaving the platform negotiates a facing left hand point on the curve, a facing right hand point, on the straight and a trailing point coming in from the left. They are all Peco streamline short points. The overhang on the Mk2 Pullmans is horrible. If my room had been about two feet wider and three feet longer I would have used larger radius points and put in a section of straight track at the centre of the reverse curve.