0 gauge fine-scale on tight radius curves

[Nearholmer]

There is a discussion that rumbles-on in my main thread, about what might be called "minimum radius" modelling using 0 gauge with G0G fine-scale wheel-sets.

 

While it does have some connection with the avowedly old-fashioned and coarse-wheeled subject of my thread, it also has quite a dis-connection, and is more likely to be of interest to more people than would ever get excited about old tinplate trains with coarse-flanged wheels running on track with a prominent centre conductor rail ....... it is very relevant to modern r-t-r plastic 0 scale for instance.

 

So, here is a new thread for people to discuss what the practical minimum curve radii are, couplings, how to avoid buffer-locking, etc. 

 

Coarse-scale can indeed teach some lessons here, particularly the "fairly fine coarse" made by Leeds Model Company in the 1930s, because they cracked all these problems "back in the day", but the subject is really one for finer-wheeled people than I.

 

Here is a nice old Leeds engine for people to admire in the meantime - notice the lack of flanges on the centre wheels, which allow it to go round 24" radius curves.

 

 

And, here is the Leeds solution to buffer-locking: super-wide buffers. There are other solutions.

 

 

 

Edited November 4, 2020 by Nearholmer

[brossard]

I assume when you refer to "minimum radius" you are talking about the GoG standard which is, IIRC, 4'.

 

My first layout iteration had a curve around the end of my basement.  The radius of this was about 4'6".  This worked surprising well and I was able to propel stock around it, using standard buffers and 3 link/screw link couplings, without lock.  Buffers and couplings do need to be sprung IMO.

 

 

The loco being used is important.  My friend has a 0-4-4T and the curve proved too much for it as the bogie swing meant that buffers locked up when propelling.

 

I ended up abandoning the notion in favour of a BLT.

 

John

Edited November 4, 2020 by brossard

[Nearholmer]

5 minutes ago, brossard said:

I assume when you refer to "minimum radius" you are talking about the GoG standard which is, IIRC, 4'.

 

No. I'm talking about the practical minimum, whatever that is, which with luck will emerge if this discussion takes off. It is clearly less than 48", because Peco sell a goodly amount of set-track, which is c40" radius, around which people presumably run trains.

[brossard]

Ah, OK, I will follow with interest although the question is academic for me.

 

John

[whizzo]

HI Every one , i am very interested in this - and wonder if it is possible to get down to 3ft 6" dia if so i can use both sides of the loft , i am only running  0-6-0 tanks  , + b set, but the curves are out of sight ( not too worried what it looks  like  )- does any one know about transition curves ???  also could it be applied  to peco set track  40" -- and tighten it down to 3ft 6"  thanks for reading.-  regards  Dave 

[Donw]

When I raised the topic in the Gauge 0 gazette twenty odd years ago I got a lot of interesting responses.  It seemed that with a bit of effort  a lot of people had managed to get all sorts of things round corners. Frank Roomes showed an LMS 4-6-0 with full flanges, brakes and sanding gear which went round a 42 inch curve. Derek Loe had a US layout in his garage with some tight curves some of the siding went down to 3ft or less. Quite big locos were able to negotiate them, as did my pannier tank. 

A few years ago I had started a lot layout and tested a lot of my stock on a 4ft curve.  This was reported in my loft layout thread and I include three photos blow. However having moved and with a 11ft8in x 9ft space 4ft will be too limiting. So I am wondering how much further could I go.

Don

 

[woodyfox]

I work to a more generous radius of about 1600mm only because one of the fundemental aspects that make models look realistic is as near a prototypical ride height as possible. This tends to diminish (allowances increase) as the radius tightens. Just a personal preference of course. 

[Donw]

25 minutes ago, woodyfox said:

I work to a more generous radius of about 1600mm only because one of the fundemental aspects that make models look realistic is as near a prototypical ride height as possible. This tends to diminish (allowances increase) as the radius tightens. Just a personal preference of course. 

 

Yes big curves do look better but when you have a smaller space than would be need for such curves it is necessary to compromise either have a simpler layout or tighter curves.

 

The usual minimum for passenger trains was I believe 4 chains which is 1.828m in 7mm but that would have been subject to a severe speed restriction and need to be checkrailed.  So we compromise how far is a matter of personal preference.

 

I was on a special which took the SLOUGH west curve coming from Windsor about 4 chains I believe. Dead slow wheels squealing away our models do not replicate that feeling.

 

Don

[woodyfox]

4 minutes ago, Donw said:

 

Yes big curves do look better but when you have a smaller space than would be need for such curves it is necessary to compromise either have a simpler layout or tighter curves.

 

The usual minimum for passenger trains was I believe 4 chains which is 1.828m in 7mm but that would have been subject to a severe speed restriction and need to be checkrailed.  So we compromise how far is a matter of personal preference.

 

I was on a special which took the SLOUGH west curve coming from Windsor about 4 chains I believe. Dead slow wheels squealing away our models do not replicate that feeling.

 

Don

Yes, the squealing of wheelsets entering Waterloo station always grated on me. Just reminded me of something i've never seen modelled, the greasing blades with container sited at the entry to tight curves. Might do a couple of those! 

As i model diesels, my main consideration is the wheel flange striking the sole bar or bogie swiping the fuel group - it's usually one or the other below about 5 foot. 

Cheers 

[Northroader]

I think there’s two ways of approaching this. Generally the question arises when someone wants to do an oval layout in a loft, garage, or shed, with 0 gauge. Thinking about my garage, you’re looking at around 16’ x 8’, and it’s best to convert it to an equivalent size in 00, which is easy to visualise and in most modellers experience, and comes in at around 9’ x 5’. Its an improvement on a 6’x 4’, but the end curvature is still quite tight. Peco do setrak now for both scales, and these have the distinction of  carrying the curvature on through the diverging track, so they’re tailored for oval layouts really. What kind of locos would you expect to run on 00 setrak? What Train length would be practical on a 9’ x 5’? How has something like a Princess Elizabeth Pacific been modified to go round this sort of curve? Everything is still going to be a squeeze and a compromise. The range of Dapol RTR 0 gauge in the recent years, all small Locomotives, will take the curves, and the type of trains that would appear with them will determine the nature of the layout.

The other side of the question is how tight can you get away with? On visits to Telford Guildex, I was always intrigued by the Agenoria models stand, which had a showcase with lovely brass kits of mainly 0-4-0 tanks, and at the base there was a very small oval with one of these engines chasing round. I made a 3’ square baseboard, with a circle and two sidings, very whimsical.  The ruling radius was 13”, and track laying involved the use of check rails on the approach to the points and at joins. Two or Three axle tank engines were involved, but only single drivers or four coupled, not six coupled. Carrying wheels were mounted so one pair could swing freely. Trains were short body four wheeler coaches and wagons. Couplers were the problem, you needed to have long rigid links free to swing and prevent the buffers from ever touching. Kadees worked well, if I did it again I would have magnets on the links at the join to prevent knuckling when propelling, which was giving me the worst problems.

[Metropolitan H]

I'm surprised that no one has yet mentioned the Lima 4F as an example of an 0-6-0 and tender with fine(ish) scale flange, but slightly wide treads that happily ran round their 2 foot radius curves - FB steel rail of similar section to Peco Code 100 formed into set-track sections. The one I had is now de-motored and used by the Grand-Childer-Beasts - despite having flanges on all wheels it works fine on the largest radius "Big-Jigs" wooden track curves - which amazed me!

 

Nearholmer - I will lend you my copy of the latest GOG Gazette, when I have finished reading it - probably next week.

 

Regards

Chris H

[Izzy]

Having just built myself what could be called a micro-minimal plank in 7mm and using 36” wyes (basically A3’s) I think what radius can be used varies depending on a number of factors. The first is what finescale standard is used. 32mm will give much more leeway than 31.5/31.2mm here as will the length of stock. If you are prepared to build your own track then gauge widening opens up more possibility of tighter radius. Not having reverse curves or pointwork on the tightest bits is probably part of the bargain to be made along with what you are prepared to accept in the way of appearance, not only the track but how the rolling stock is made/adapted to cope with it. Generally though I think that it’s inevitable that the bigger the stuff you want to run the more space you need to do so once track & wheel standards get finer. I always thought 6’ was considered the minimum for finescale, but probably to cover the biggest/longest stock. 
 

Izzy

 

 

Edited November 4, 2020 by Izzy

[kernowtim]

A relative of mine built a test track using peco SM32 set track curves of 30 inch radius, and discovered that his Heljan class 45 diesel would just about run  on them although it did look a bit odd!

[F-UnitMad]

8 hours ago, Izzy said:

I always thought 6’ was considered the minimum for finescale, but probably to cover the biggest/longest stock. 

Indeed. My Heljan 31 & 37 can actually negotiate 36" radius curves, but their overhang precludes them pulling any stock - even with the gentlest of transition curves the couplings wouldn't stretch far enough. It's the lack of an O scale equivalent of the 4mm tension lock coupler that hinders curve radius for UK stock - but in fairness I for one got into UK O  precisely because I wanted to use scale couplers, instead of tension locks.

Of course with buckeye couplers & no buffers, American stock is no so constrained, but even then, with modern diesels & long rolling stock I have found 36" radius curves to be the practical minimum; tighter than that & stock will contact each other, especially being propelled. Atlas does state that the minimum radius for most of it's stuff is 36", at least for diesels. No idea or experience of what radius steam locos would need.

Video of my biggest US diesel, Atlas SD40, taking a 36" radius curve....

 

[goldfish]

Lenz, which I believe would be classed as fine scale, use a minimum radius of 914mm and a flange depth of 1.15mm. They guarantee that their BR502-10-0 will negotiate their minimum radius, which is quite something given that it appears to have flanges on all ten driving wheels. They get around the problem of buffer lock etc. by using a rather massive coupling system.

 

 

Lenz track is actually manufactured by Peco and is much like Peco Streamline flat bottomed track. I did ask Peco support why they only supply R2 Setrak, and was told that they consulted various bodies, mainly the G0G and were assured that there was no market for R1 curve in the UK. Lenz R1 track is available in the UK, alternatively ETS supply 625mm curves using code 175 rail.

 

Dapol apparently design their products to negotiate 40" curves (R2) but some of their rolling stock will happily negotiate 625mm reverse curves.

[Nearholmer]

11 hours ago, goldfish said:

consulted various bodies, mainly the G0G and were assured that there was no market for R1 curve in the UK.

 

And how, pray, do the G0G know that? They don't, do they?

 

Sometimes products make their own market, by opening-up possibilities that never existed before.

[goldfish]

21 hours ago, goldfish said:

I did ask Peco support why they only supply R2 Setrak, and was told that they consulted various bodies, mainly the G0G and were assured that there was no market for R1 curve in the UK.

 

I asked this question during a telephone conversation about Peco points. During the same same conversation I was told that there was no market for universal points.

[Hal Nail]

In fairness they aren't saying there is literally no market, just that in a traditionally small pool of O gauge modellers to start with, they believe that even fewer would want 1st radius to warrant risking the investment, when there are other gaps manufacturers can fill.

 

The ability to fit a small tank and 4 wheelers into a tight space, even if longer stock couldn't cope, would clearly appeal to some but not by any stretch everyone, which impacts on the economic feasibility.

 

Whether their opinion of the market is changing as rapidly as the market is an interesting question though. R-T-R is covering early era wagons with little BR appeal now and you definitely wouldn't have seen that coming a few years back.

 

 

 

[F-UnitMad]

This could easily slide into "How R-T-R O Scale has progressed despite, not because of, the 'Gay Joe' Guild....  

[goldfish]

It should also be remembered that at the time when Peco was looking for advice, the market was very different. They were doing market research in anticipation of launching O gauge Setrak, that introduction into the market has changed everything.

 

But there is something of a chicken and egg situation here. Peco decided that there was not a viable market for R1 curves and so only produced R2 curves for the UK market. So any manufacturer looking to produce R-T-R locomotives and rolling stock is going to design them to suit R2 curves, because that is perceived the smallest radius that the UK market requires. How different would the market look today if Peco had taken the decision to produce R1 Setrak curves? Presumably Dapol would have designed the Terrier to run on them, and the Dapol Terrier was key to how the market is evolving now.

 

The situation, as I see it, is akin to the transition from Honby Dublo 3-rail to Hornby Dublo 2-rail, or rather the market transition that took place at the time. The market demanded 2-rail, and that is what it got. The current O gauge market seems open to smaller curves, and presumably that is what it will get.

 

[JinglingGeordie]

This was a concern for me when I took up 0 gauge a few years ago. This was before the RTR 040  and 060s so I was thinking of either kit building or commissioning a kit builder. I did find the DJh website useful as recommended minimum radius curves (6 foot in most cases). 

 

Talking to other gauge 0 modellers it was agreed that minimum curves is a difficult topic to nail down. A 040 will go round quite tight curves, but wagons will need lengthened chains on their couplings. 060s with enough lateral movement will go round tighter curves than ones with tighter axle movement. Add a bogie or pony wheel and maybe yes maybe no. Cleminson axles on 6 wheel coaches, perhaps would work. Add larger buffer heads and that may help.

 

A lot of maybe aye, maybe make, which is frustrating. Also the modeller using RTR now may want to tacklea kit in the fullness of time. But will it run? 

 

I was advised 6 foot radius or think end to end. I guess the advise is think 4.5 foot or end to end OR risk it....

 

Good luck with whatever you try.

[Donw]

When I said earlier about having raised the topic in the Gazette. I didn't mention that I was the editor then and received a lot of comments there has always been people interested in using tighter curves. I dont think the Guild's advice of curves has been that helpful but on the other hand start recommending using tighter curves and people will be complaining 'you said it would be ok'.

The truth is some work may be necessary on some models such as kits . No difficult but you really need to build it to run on the curves you want.

On loco with outside valve gear you may find you need minimal side play of the front driving wheel due to the valve gear and plenty of side play on the middle and rear driving wheels. The Gap between the loco and tender needs to be sufficient for your curves etc.

One thing about tight curves, from inside the curve the gaps between stock close up on curves from the outside they open up. A home layout with a tight curve against the walls of a room/shed looks much better than the same curve viewed from outside on ssay an exhibition layout.

 

Don

[whizzo]

please may i ask, has anyone - tried  running a Dapol - 3f Jinty  or a57xx on -- lenz r1  914 mm Dia  if so -- it would work for me ///   or would a lenz r1 track  -- fit peco  r2 set track ???  - if  one  lenz  r1 was placed in the middle of a half circle of  peco r2s  would this work ???-- could this be classed as transition curve ????   it does not matter what it looks like as the curve would be out of sight -- thanks for reading and your comments , regards Dave 

[Donw]

2 hours ago, whizzo said:

please may i ask, has anyone - tried  running a Dapol - 3f Jinty  or a57xx on -- lenz r1  914 mm Dia  if so -- it would work for me ///   or would a lenz r1 track  -- fit peco  r2 set track ???  - if  one  lenz  r1 was placed in the middle of a half circle of  peco r2s  would this work ???-- could this be classed as transition curve ????   it does not matter what it looks like as the curve would be out of sight -- thanks for reading and your comments , regards Dave 

 

It would work so long as the loco can manage the R1 curve.

Transistions to curve are particularly useful to reduce the mismatch at couplings.  The biggest mismatch occurs at the start of a curve.  Consider two coaches on a curve the ends will overhang the track but if both are on the curve both will overhang outwards  so the couplings are not too far apart. Consider now where one coach is on the curve while the other is on the straight. The first coach has the end overhanging the track while the second one still has the end central to the track. This is maximum mismatch between the couplings well not quite if you are daft enough to connect two curves of opposite radius together without a bit of straight inbetween the two ends overhang in opposite directions at the join giving double the mismatch.

Consider now if you have a straight track then a piece of 5ft curve leading to a 3ft curve. The mistmatch at the two changes from straight to 5ft and 5ft to 3ft will both be less than going straight to 3ft and it will thus act as a transistion. A full transistion is a continually increasing curve from zero to the max but it is simple and effective to just use two different curves. The wider radius piece should be as long as your longest piece of stock. Do be aware through this can still steal a few valuable inches if things are really tight.

The astute among you may now be saying what about a crossover. It is true a crossover does change radius between the two ends and it may give trouble if at the minimum radius. However say you have a simple terminus with a release crossover to run round the train. This will generally only be used by the loco on its own or possible with a short van or horsebox tail traffic and not long coaches. So may give trouble. However  if you have a trailing crossover common in double track through stations where it is normal to back a train over the crossover  in some moves a crossover at your minimum radius may well be a trouble spot.

Sometimes you can arrange the crossover at the junction of the straight and the tight curve so the train is backed over the first turnout but the second being on the curve it straight for the backing train. 

I will try and do some drawings to make this clear.

 

Don

 

[F-UnitMad]

6 hours ago, whizzo said:

please may i ask, has anyone - tried  running a Dapol - 3f Jinty  or a57xx on -- lenz r1  914 mm Dia  if so -- it would work for me ///   or would a lenz r1 track  -- fit peco  r2 set track ???  - if  one  lenz  r1 was placed in the middle of a half circle of  peco r2s  would this work ???-- could this be classed as transition curve ????   it does not matter what it looks like as the curve would be out of sight -- thanks for reading and your comments , regards Dave 

If my maths is correct and 914mm is about 36 inch radius in Old Money, give or take a bit, then I can confirm that my Dapol & Minerva 8750 Pannier Tanks can get round them, and even manage to push & pull stock too, although sprung buffers are desirable.

Don't know about the Jinty as I don't own one, but I should imagine it would cope too.