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O gauge loop size - larger than set track


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I've been building a garden railway and the first of two reverse loops I built with Peco set track. I subsequently found this to be too tight a radius for some stock buffer locking :unsure:

 

I'm running modern image RTR stock, I'd like to be able to get at least a Heljan Class 37 round, ideally something as large as the Class 60 but I'm willing to compromise.

 

What would people suggest as a minimum radius?

 

Thanks! 

 

 

 

Edited by dan_the_v8man
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I think the answer is, as large as you can make it. If you're constrained by fences, then that's as big as you can go. If you have the space, make it bigger. Sorry if that doesnt help much, but it is a "how long is a bit of string" question!

Guess you could get somdd flexitrack, lay some out and see how it goes.

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12 minutes ago, ikcdab said:

I think the answer is, as large as you can make it. If you're constrained by fences, then that's as big as you can go. If you have the space, make it bigger. Sorry if that doesnt help much, but it is a "how long is a bit of string" question!

Guess you could get somdd flexitrack, lay some out and see how it goes.

 

I need to keep it as small as practical to appease the wife unfortunately! 

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Looking at Antics website (https://anticsonline.uk/Category/Peco-Track-O-Gauge_N475), the set track points seem to have a radius of 40".

 

The next step up seems to be a nominal curve radius of 72", which is probably what you should be aiming for, albeit I note that the curved point has an inner radius of 68", so if you can't get to six foot radius, then I've thought that must be perfectly satisfactory.

 

I don't model in 0 gauge, but in 00, I'm aiming for 30" minimum, so multiplying that by 7/4 would give a minimum of 52.5" - would that be achievable?

 

 

 

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On 20/09/2020 at 21:14, Dungrange said:

I don't model in 0 gauge, but in 00, I'm aiming for 30" minimum, so multiplying that by 7/4 would give a minimum of 52.5" - would that be achievable?


In 0, the practical minimum radius is very critically dependent upon the length of the stock, more specifically the ‘end throw’ For coupler purposes and buffer-locking reasons, and both end and centre throw for passing on curves. 
 

For finescale, 72” radius is often cited, and that will do for most things but, as the Peco set-track range proves, for short locos and wagons 40” radius is OK.

 

R-T-R 00 tends to be a bit simpler, because nearly all of it will run round ‘second radius’, which IIRC is c17.25” - the RTR designers build-in the compromises to allow that.

 

Unfortunately, it isn’t always possible to make a direct 00 to 0 conversion, even for models of the same stock/loco, because the 00 ones often have, in scale terms, much greater clearances built into them, and if tension-lock couplers are used they obviate buffer-locking. 
 

 

 

 

Edited by Nearholmer
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Usual cause of "Modern Image" as in post 1968 buffer locking is running the buffers in the extended position where the full size stock has the buffers retracted between coaches and only extended when screw coupled to locos etc.   

My OO late 80s era garden layout had a 3ft ish radius reverse loop which gave endless trouble with derailments on 64ft and 75ft stock which pulled off inwards and was eventually abandoned and it became end to end.

As others have said 60" or 72" sounds good but just make them as big as possible.  My garden layout was 90% ground level and crossed paths on the level and burrowed under a rockery which minimised wife/ partner garden space issues.   It became on board battery powered after power leakage problems and is still on the to do list for upgraded Radio Control, when I find some which works when trains are a foot deep in a six foot tunnel under the rockery.  Without on board power the fiddling to operating ratio struggled to dip below 50:1.   After it I was attacking snow drifts with pairs of 37s and a snow plough.

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11 hours ago, Nearholmer said:

For finescale, 72” radius is often cited, and that will do for most things but, as the Peco set-track range proves, for short locos and wagons 40” radius is OK.

 

R-T-R 00 tends to be a bit simpler, because nearly all of it will run round ‘second radius’, which IIRC is c17.25” - the RTR designers build-in the compromises to allow that.

In my experience of Heljan O diesels, they'll run through a radius as tight as 36" yes, 3ft - but they just won't pull any stock through it!!  The reason being the absense in O scale of the biggest compromise of all in OO (my bold in quote above) - the Tension Lock Coupler!!!

Even various after-market auto couplers in O don't really allow for tight curves - for most UK outline 'mainline' locos and stock, 6ft radius is really the minimum to go down to without any issues at all.

 

My main layout is U.S. outline - so no buffers and a prototypical auto coupler; that's why I can get a 17ft x 8ft roundy-roundy in my loft with 3ft radius curves. I don't feel smug about it at all, in any way whatsoever.... :mosking:

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On 22/09/2020 at 00:52, DavidCBroad said:

Usual cause of "Modern Image" as in post 1968 buffer locking is running the buffers in the extended position where the full size stock has the buffers retracted between coaches and only extended when screw coupled to locos etc.   

My OO late 80s era garden layout had a 3ft ish radius reverse loop which gave endless trouble with derailments on 64ft and 75ft stock which pulled off inwards and was eventually abandoned and it became end to end.

As others have said 60" or 72" sounds good but just make them as big as possible.  My garden layout was 90% ground level and crossed paths on the level and burrowed under a rockery which minimised wife/ partner garden space issues.   It became on board battery powered after power leakage problems and is still on the to do list for upgraded Radio Control, when I find some which works when trains are a foot deep in a six foot tunnel under the rockery.  Without on board power the fiddling to operating ratio struggled to dip below 50:1.   After it I was attacking snow drifts with pairs of 37s and a snow plough.

Funnily enough that's why I've avoided tunnels and I'm only running radio control in the garden! 

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Marcway do rtr points & kits of 48 in radius, as well as 72 in.  You might be pushing it to get a 37 through the 48in ones (but see above), though as the 6 wheel bogie is fairly short it might.  My long wheel base 0-4-4 would just go through 48 in points.  I simplified my layout to increase the radius.  Buffer locking can be avoided by shorter stock, glueing a piece of stiff wire across the buffers so the heads can't get behind each other, or adding an extra / longer link into the couplings.

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9 minutes ago, duncan said:

Marcway do rtr points & kits of 48 in radius, as well as 72 in.  You might be pushing it to get a 37 through the 48in ones (but see above), though as the 6 wheel bogie is fairly short it might.  

As I posted earlier, my HJ 37 (& 31) will go through 36" radius no problem. It's the lack of a coupler like the 4mm tension lock that prevents them pulling or pushing stock through it.

Think of it this way - 4mm diesels can go through R2 curves, which is 18" radius? Take the tension lock couplers off them, and see if they can pull stock using scale 3-links through that curve now.... :no:

Buffer locking can be avoided by shorter stock,

True, but the OP was specifically asking about longer locos & stock.

glueing a piece of stiff wire across the buffers so the heads can't get behind each other, or adding an extra / longer link into the couplings.

:shout:Aggghhhh!!!! Wires across buffers are HORRID, nasty things!!! NO!!! :nono: my 'pet hate' about the Sprat & Winkle coupler!! - anyway O scale stock has sprung buffers which wouldn't help trying to stick a rigid wire to, and adding an extra link in the coupler chain only works when pulling stock, not pushing.

Just my observations, based on experience. :)

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You can only get buffer locking if you have reverse curves, so look to eliminate those.

 

Or do you mean the couplings are too short, resulting in stock being thrown off?

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11 minutes ago, Tim V said:

You can only get buffer locking if you have reverse curves, so look to eliminate those.

 

Sorry, but that is just plain wrong. If the curve radius is too tight relative to the length of the rolling stock, there will be buffer locking, even on a plain curve.

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29 minutes ago, F-UnitMad said:

Sorry, but that is just plain wrong. If the curve radius is too tight relative to the length of the rolling stock, there will be buffer locking, even on a plain curve.

 

Agree. This is one of the reasons for using transition curves between straight track and constant radius.

 

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45 minutes ago, Harlequin said:

 

Agree. This is one of the reasons for using transition curves between straight track and constant radius.

 

Agree in turn, but even with transition curves, if the constant radius is too tight for the length of the rolling stock, buffers will slide past each other as the track straightens out again.

Guess how I know.... ;)

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Clearly you haven't read the works of Peter Denny. You are describing a different phenomena. The buffers should not be in contact when pulling. Therefore they will not cross.

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15 minutes ago, Tim V said:

Clearly you haven't read the works of Peter Denny. You are describing a different phenomena. The buffers should not be in contact when pulling. Therefore they will not cross.

   :banghead:  :banghead:   :banghead:

 

Pulling - if the curve is too tight, the buffers will meet - then pass each other, and lock as the track straightens again.

Pushing - the buffers are in contact, doing what they're designed to do. If the radius is too tight, yaddayaddayadda - what is that phenomena called then if it's not buffer locking? It's the same end result!! :rolleyes:

I have read the works of Peter Denny. As far as I know he never ran mainline B.R. diesels and coaches.... :no:

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58 minutes ago, F-UnitMad said:

Agree in turn, but even with transition curves, if the constant radius is too tight for the length of the rolling stock, buffers will slide past each other as the track straightens out again.

Guess how I know.... ;)

Agree but if you design your transition curves correctly, they will not allow the buffers to slide past each other.

:smile_mini:

28 minutes ago, Tim V said:

Clearly you haven't read the works of Peter Denny. You are describing a different phenomena. The buffers should not be in contact when pulling. Therefore they will not cross.

If your reverse curves & transition curves allow you to propel stock through them without buffer locking then you have truly found Nirvana.

:railway bhudda:

 

Edited by Harlequin
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2 hours ago, F-UnitMad said:

   :banghead:  :banghead:   :banghead:

 

Pulling - if the curve is too tight, the buffers will meet - then pass each other, and lock as the track straightens again.

Pushing - the buffers are in contact, doing what they're designed to do. If the radius is too tight, yaddayaddayadda - what is that phenomena called then if it's not buffer locking? It's the same end result!! :rolleyes:

I have read the works of Peter Denny. As far as I know he never ran mainline B.R. diesels and coaches.... :no:


And thats exactly what I'm experiencing! 

I think i'm going to go for a 60"/5ft radius on the new loop then :)  

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10 hours ago, dan_the_v8man said:


And thats exactly what I'm experiencing! 

I think i'm going to go for a 60"/5ft radius on the new loop then :)  

Be interesting to know if 5ft works for modern stock. My gut feeling is that that's still pushing it, 6ft would be better, but test as you go. 

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43 minutes ago, F-UnitMad said:

Be interesting to know if 5ft works for modern stock. My gut feeling is that that's still pushing it, 6ft would be better, but test as you go. 

I have a Dapol 7 mm scale B set.

 

It can be pulled through a 4' 6" radius curve, but the buffers on the inner side are almost fully compressed.  The sprung screw coupling hooks are  visibly pulled away from the buffer beam.

 

Try to propel it through the same curve, and with without any transition to ease the initial entry, you get buffer locking.

 

I also tried them on 'South Greenfield'  a US outline layout (recently dismantled, which had 4' radius curves.  They would run through whilst being pulled, but struggles when being propelled, coming out of the curve invariably caused buffer locking.  The US outline stock with no buffers and Kaydee couplers had no problems.

 

As you can see by this and many other posts the issue lies not with the ability of the stock to traverse a tight curve, but the buffing and coupling arrangement that causes the problem. within reason when a train using such a coupling system is being pulled through a curve, it is less of a problem than when it's being propelled and the buffer heads are in contact.

 

My advice is sort out your minimum radii by experimentation.  Get some ply sheet, (or even use the dining room table!)   some strips of  double sided tape and a couple of lengths of track and lay out the curves from a hard entry (no transition) and then pull and push your stock through it.  That will give you a rough idea of how large or small you can go.

 

But remember that is only good for the stock you already own, newer and ever longer stock might not work!

 

 

 

 

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The bare truth is that with long stock you Can either have tight curves or Prototypical couplings/buffing. You can’t have both together.

 

Using various ‘dodges’ on coupling/buffing does work: wires across buffer-faces, rigid-link couplers, extra-wise buffers, that sort of thing.

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Hi all,

From running a 16mm narrow gauge garden railway we found that 6ft radius was the smallest but 8ft was more preferable and easier for the loco's to negotiate. I only say this as 16mm narrow gauge use the same gauge track as 0 gauge. But to be honest bigger you can get it is better when it comes to looping track round bends.

Edited by cypherman
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5 hours ago, Happy Hippo said:

I have a Dapol 7 mm scale B set.

 

It can be pulled through a 4' 6" radius curve, but the buffers on the inner side are almost fully compressed.  The sprung screw coupling hooks are  visibly pulled away from the buffer beam.

 

Try to propel it through the same curve, and with without any transition to ease the initial entry, you get buffer locking.

 

I also tried them on 'South Greenfield'  a US outline layout (recently dismantled, which had 4' radius curves.  They would run through whilst being pulled, but struggles when being propelled, coming out of the curve invariably caused buffer locking.  The US outline stock with no buffers and Kaydee couplers had no problems.

 

As you can see by this and many other posts the issue lies not with the ability of the stock to traverse a tight curve, but the buffing and coupling arrangement that causes the problem. within reason when a train using such a coupling system is being pulled through a curve, it is less of a problem than when it's being propelled and the buffer heads are in contact.

 

My advice is sort out your minimum radii by experimentation.  Get some ply sheet, (or even use the dining room table!)   some strips of  double sided tape and a couple of lengths of track and lay out the curves from a hard entry (no transition) and then pull and push your stock through it.  That will give you a rough idea of how large or small you can go.

 

But remember that is only good for the stock you already own, newer and ever longer stock might not work!

 

 

 

 


Excuse my ignorance but whats a transition curve? 

(this is my new proposed loop at 5ft radius) 

loop.JPG

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