Tension lock coupling standards in 4mm

[Miss Prism]

Are there standardised values for a, b, c and theta?

 

 

 

Edited April 21, 2022 by Miss Prism
reinstated image

[The Johnster]

My experience of t/ls suggests that, if there are standard sizes and values, nobody keeps to them even within one manufacturer's range; different bar heights and profiles, different hook profiles, different dropper profiles and all available in different materials are common, and the couplers' reliability despite this is a testament to the soundness of the basic design.

 

An element of standardisation has come about with NEM pockets, but only applies to the pockets and not to their mounting or the precise details of the couplers mounted in them.

[timbowilts]

To paraphrase the Johnsters reply in one word “No”

 

Tim T

[timbowilts]

What we all need to remember is what the first ones looked like

[Il Grifone]

The above Mk II isn't a tension lock, but is theoretically compatible with the Mk III. The height of the top of the bar above the railhead (a) is critical (It's about 10mm - I'll have to measure one). The projection beyond the buffers (b) depends on the radius involved. It was originally designed for 13½" radius curves, so is generously dimensioned. The dropper rail clearance can vary as it will depend on the height of the uncoupling ramp and and the hook striking angle angle (θ) can vary considerably without affecting operation. Somewhere in the range 30º - 45º seems reasonable. 

 

SInce the wretched thing is a Tri-ang Invention*, I would take their settings as the standard.

 

Personally i prefer the Peco/HD coupling. This does have specific standard dimensions and works very well if these are maintained. The Continental loop coupling is also superior IMHO**, but suffers from incompatibility between makes.

 

* In this form. It's origins are to be found in the LaNal coupling of 1929 or thereabouts.

 

** Both can be easily uncoupled by simply lifting a vehicle by hand.

Edited October 1, 2017 by Il Grifone

[The Johnster]

To paraphrase the Johnsters reply in one word “No”

 

Tim 

 

Yes.

[locomad]

 

Personally i prefer the Peco/HD coupling. This does have specific standard dimensions and works very well if these are maintained. The Continental loop coupling is also superior IMHO**, but suffers from incompatibility between makes.

 

.

So do I, since I've finished tracklaying a larger layout, the benefits of the peco/HD coupling are clearly showing over the tension lock especially longer trains is those over 20 wagons or 8 coaches.

 

Clearly there are no standards for tension lock, even triang,/ Hornby ones vary greatly between stock, never mind mixing in the airfix, mainline Lima modern Hornby. I've even found NEM course problems as coupling seam to pull out.

 

Getting a train round even with just 20 wagons seems to be impossible, stock uncoupler, derails, and even trying to shunt such a train is a nightmare as they simply lock up.

 

Then there's the gap between stock far to unrealistic

 

Far less problems with peco/HD no worries about reversing 40 wagon train, and fewer de coupling incidents while operating, and a lot easier to hand uncouple.

 

I agree on the whole tension lock uncouplers are more likely to work, but properly tested and maintained peco/HD are not that far behind

[Miss Prism]

Having had a google and seen the bewildering array of tension locks (good grief!), it seems that Hornby's latest NEM-plugins, assuming that Hornby's pockets are conformant, will make dimension a the standard NEM362 pocket height of 8.5+/-0.2mm.

 

Dimension c is I guess very close to 3mm.

 

Approx 40 degrees for theta seems common.

 

Dimension b is the interesting one, and yes it is curve dependent, but on second radius curves, could be as low as 3.5mm minimum for a lot of stock without incurring buffer bumping. In practice, it will probably need to be greater than this, not because of the curve constraint, but because of the need to get a viable hook axis position that will not interfere with the NEM362 pocket (the front of which is only 7.5mm behind the buffer face).

[Miss Prism]

Is there a drawing of a Peco/HD?

[The Johnster]

I had a minor crisis just under a year ago after restarting modelling after a quarter century gap caused by, um, life, red in tooth and claw.  Such stock as had survived the various upheavals was a mix of kit and RTR with scale couplers, but it very quickly became apparent that I no longer have the dexterity, clarity of sight, or hand/eye co-ordination to cope with these, and, after a short period of soul searching reverted to tension locks, despite their undoubted problems of appearance and lack of standard.  Kadees I dismissed owing to not being happy with a few other things going on at the same time with having to take on a steep learning curve of what numbers fitted what applications, and they are anyway just as ugly on steam era stock as tension locks, and I rejected Sprat/Winkle and derivates on the basis that they are fiddly to set up, though clearly excellent performers once installed properly.  I considered Peco/Hornby Dublo but eventually opted for t/ls as being easily obtainable from local outlets, and hence a project I could get underway with immediately.  I don't like fixed points for uncoupling by magnet; on a real railway any stock can be uncoupled martini style, any time any place any where...

 

I realised very quickly that the lack of standardisation was going to cause problems especially as many of the items of stock had had their original tension lock mounts cut away to install scales.  In fact the problems of getting a consistent bar height and ensuring droppers were trimmed to clear rails at turnouts were considerable, but I persevered, and now have an entire layout of stock with couplings that work with each other.  I still have to examine my trains before setting off with them to ensure that both hooks have engaged both bars on both vehicles to ensure reliability, but with that precaution taken performance has been to all intents and purposes 100%; my trains do not uncouple in service.  Uncoupling when I want to, with a shunting pole, was a faff at  first but I can now achieve it fairly reliably in all locations that it is necessary to do so.

 

But if I were starting again in this situation, I would certainly be giving greater consideration than I did to Peco/HD couplers.  I remember them from my childhood as being unreliable if any changes in level and many in direction were involved, but trackwork tended to be rougher and readier in those days and I can see no reason why they would disengage on my current layout where all is level and carefully laid, nor I imagine would any buffer locking issues raise their heads.  They have the advantage that vehicles can be easily 'crane shunted' out of a train on a fiddle yard road, which I thought desirable for unloading and loading coal wagons.  The direct overhead operation of the shunting pole is an advantage, but not a deal breaker as it turns out!

[DCB]

Inside I use Tension locks between coaches but with usually Mainline couplings re mounted to close up the gaps between vehicles and never uncouple the rakes. For locos, wagons and the ends of rakes I use H/D peco style couplings.  The garden is Tension Locks only so I have experience with both.  The simple answer is with Tension locks you have fiddle about to get the height right, changing wheels perhaps.    I cobble up a set of templates and adjust all the couplers so the coupling "loop" to be within 0.5 mm of datum height or one vehicle will lift its neighbour enough to derail it. The old Triang metal coupling is the easiest to tweak, but the tweaking will often put the droppers too high or low  for uncoupling ramps. or else they get stuck in points.  

The NEM Pockets are good in that you can mix and match to get the couplers to get the heights better.   To be honest if I were starting again I would look in to using the N gauge couplers for 00,  Kadees work well but look a bit too American for me.

[Dunsignalling]

Having had a google and seen the bewildering array of tension locks (good grief!), it seems that Hornby's latest NEM-plugins, assuming that Hornby's pockets are conformant, will make dimension a the standard NEM362 pocket height of 8.5+/-0.2mm.

 

Dimension c is I guess very close to 3mm.

 

Approx 40 degrees for theta seems common.

 

Dimension b is the interesting one, and yes it is curve dependent, but on second radius curves, could be as low as 3.5mm minimum for a lot of stock without incurring buffer bumping. In practice, it will probably need to be greater than this, not because of the curve constraint, but because of the need to get a viable hook axis position that will not interfere with the NEM362 pocket (the front of which is only 7.5mm behind the buffer face).

IMHO, there's only one sensible solution to the NEM mountings as applied to about half of UK outline r-t-r, evidently without regard to any other aspect of the specification apart from the pocket itself.

 

Xuron track cutters.

 

John

[Il Grifone]

Is there a drawing of a Peco/HD?

 

There must be somewhere or I could measure some up. IIRC there is an article on-line somewhere about the geometry and how to modify it for the best results.

 

The critical measurement is the coupling centre line which is the same as Kadee within reasonable tolerances. The actual value does not matter, of course, as long as they are all the same. The dropper should clear the rail by 1/32" (again the same as Kadee) and the coupling hook should be 1/8" in front of the bufferheads. It is recommended that this be lengthened to 3/16" for sharp curves, but I tend to ignore this as the gap between vehicles is excessive with 1/8". (It just makes coupling less reliable on curves). Dublo fitted short buffers to minimise this (as does BR).

 

Peco used to claim it would couple with Tri-ang and 3 links. It will as long as reversal is not involved. The bottom of the tension lock hook is the same height above the rail as the top of the coupling hook.

 

The Mk II Peco coupling provides for delayed uncoupling, but will no longer couple with the Dublo version, which has a slightly larger head.

 

Where necessary, I prefer the Mainline version of the tension lock. It is neater and the spring gives a more positive action. Unfortunately it is plastic but you can't have everything.

 

My dislike for the things stems from a regrettable incident where a whole (long of course) train ended up on the floor following a derailment. The tenacity of the tension locks did not allow the vehicles to uncouple and they were all dragged off the baseboard. This would not have happened with the Peco type.

[34theletterbetweenB&D]

My experience of t/ls suggests that, if there are standard sizes and values, nobody keeps to them even within one manufacturer's range...

Discarding all the earlier incarnations from consideration, the presently manufactured miniature tension locks (MTL) that I have sampled to date do at least appear to be consistent within a manufacturer's range. Reliable operation requires that one manufacturer's miniature tension lock design be used, as there is no standardisation between manufacturers; although I cannot claim to have fully tested this for the range of all RTR manufacturer's designs now before us.

 

When performing my reliability test work there were just two MTL obtainable in sufficient quantity, Bachmann and Hornby. (I didn't feel inclined to buy sixty Heljan 47s to obtain a sufficiently large test group of their couplers.) Mixed use led to occasional failures, exclusive use of one design was reliable; the qualification being that installation was correct.

 

A major benefit with the MTL is that it may be mounted for closer coupling as the user determines suitable for the layout minimum radius. In this respect the NEM coupler pocket is a useful adjunct: I de-NEM it with cutters to produce a short mount pocket.

 

Wouldn't it be nice if a RTR manufacturer devised an original, specific to 4mm design, for both coupler mounting and coupler(s) - the latter ideally with some resemblance to prototype - correctly in the prototype's drawgear position? This is not impossible and can accomodate the NEM coupler pocket option as an alternative for small radius use, as the two systems occupy different non-overlapping locations. See next.

 

... Kadees work well but look a bit too American for me.

Since they have been used in the UK since C19th, I feel they have an international passport. Bachmann use their cloned version in the bufferbeam of some of their contemporary wagon models which are operated with knuckle couplers in reality; the resulting appearance of the model is very successful. A NEM coupler mount is provided on the bogies, and the user can remove the knuckle and easily employ a different commercial coupler of choice. Best of both worlds solution.

[jcm@gwr]

They might have been in use for that long, but prior to WW11,

they were pretty much restricted to coaching stock and then

mainly Gresley and Pullman stock (I know the L&Y used them,

and others too)

The majority of coaches used screw link, and loose coupled

goods wagons, well the clue is in the name!

So I still think they look wrong on most British wagons in the

Big Four era, and especially pre-grouping.

[locomad]

. The old Triang metal coupling is the easiest to tweak, but the tweaking will often put the droppers too high or low  for uncoupling ramps. or else they get stuck in points.  

The NEM Pockets are good in that you can mix and match to get the couplers to get the heights better.   To be honest if I were starting again I would look in to using the N gauge couplers for 00,  Kadees work well but look a bit too American for me.

Going back to the standards I've never found any literature about the tension lock but tend to use my own jigs based on an average tension lock mainly the triang MK3 which as you said it's the easiest to tweak. Buying mainly 2nd stuff it's also the easiest to damage, but again easy to bend straight.

 

Your right again some get stuck in points and been metal short or flash, run a train in the dark and it can be quite spectacular, you also notice just how many times it happens. Course same thing happens with metal peco, difference been there's cross movement for peco so less likely to derail although some of them do or decouple.

 

Course there's other factors, setting the coupling static does not take into effect rolling and pitching of stock in motion, all attempts to get perfect track and still coupling play a major part in derailments and trains decoupling, I would say coupling account for 9 out of 10 "interventions" where I have to get up and sort something out.

 

Which led us to design and build my latest layout with the siding within easy reach of " hand of god", although I did discover years ago the old 2rail Hornby Dublo uncoupler is the most reliable and can cope with both systems.

[BR60103]

I found that a Lima coach coupling had the hook so long that it batted against the bunker of a Terrier rather than dropping into the loop.