Buffer Locking & Minimum Radius
Harold Jones
Photographs by the
author
I HAVE NEARLY 30 years of practical experience of using tight radius curves on my fine scale layout and find that the problem is mainly in the mind. So, before looking for solutions, I suggest you just have a play and see what is possible. The introduction to the featured layout in Issue No.0 of the Model Railway Journal suggests that we ‘ignore the tenets and protocols of conventional finescale modelling.’ I heartily agree.
My shed is some 19ft 6in. x 7ft 7in. In it I have a doubletrack mainline layout with two stations, lineside industries and townships. (My apologies for using imperial measurements; as I have said before, I cannot visualise metric measurements so to avoid errors I use what I understand.) I run normal main line stock with locos from an 0-4-0WT to 4-6-2s 2-8-0, 2-10-0 and my latest challenge, the LNER P2 2-8-2.
It is taken as read that your track is well laid with no kinks, on level baseboards and that all your stock is well maintained and is well-built to a good standard.
In all things in railway modelling, before we start devising our own solutions, we should look to the prototype for an answer.
This picture shows two
coaches on my 3ft radius
test track. As this reveals,
the buffers are in contact
and would still be on a
much tighter radius curve.
The prototype also had to avoid buffer locking. The simplest solution is to ban the use of affected vehicles wherever it might occur. This may not be practical, so practical solutions must be found. These include transition curves, larger diameter or oval buffer heads and a swivelling coupling hook such as on the BR class 4 2-6-4T.
I have never had to use extra links in the couplings, rigid
or solid couplings, bars across the buffers or any other
‘solutions’. My main aim is to operate as per the prototype,
so this requires that coaching stock can be propelled over
crossovers, reverse curves and tight radius curves in the
carriage sidings. I also add/remove coaches and tail traffic
during normal operation, using the train engine or a
dedicated shunting loco.
Two vehicles about to
enter the transition curve.
The buffers are in contact
and in line, the screw link
coupling is connected.
My use of 3ft as my minimum radius is dictated by my loco stock and available baseboard width. Buffer locking occurs at the beginning of a curve, when the angle between two vehicles, being propelled, is greatest, so if we introduce a transition curve, of sufficient length to allow the second vehicle to gradually enter the curve until the danger of buffer locking is over, then we can prevent buffer locking. My article in the May Gazette describes my method of laying track to help achieve this.
The track in the following photographs is replicating the inside curve of my double track continuous main line in my shed.
Further experience shows that you must pay attention to the configuration of the vehicles – an 0-6-0T may have a greater overhang at one end, possibly resulting in buffer locking in one direction; some coaches have the bogies set further inboard than normal, again this must be accounted for i.e., not all vehicles of the same length can be treated equally.
Both vehicles fully on the 3ft radius part of the curve. To
demonstrate how effective a transition curve is, the first vehicle is
a GWR dreadnought which is one of the longest of coaches.
Tight radius curves impose their own rules, buffers must work smoothly and gently, it helps if the coupling hook spring allows a little movement and, for bogie stock, that there is nothing to prevent the easy swing of the bogies.
Another important point is that of weight, it helps the vehicle resist the forces trying to force it to take a straight line. It also follows that the buffer beam must be of sound construction.
I have not mentioned goods stock, mainly, because if a coach can go round a 3ft radius curve, then so can a goods wagon.
My layout appeared in the November 2020 Gazette, in which I mentioned that I was now using the old Tri-ang tension lock couplings on my coaching stock.
This has nothing to do with buffer locking but it makes prototypical operation possible, as it is the only easy way in which I can remotely couple/uncouple stock which is out of sight under the buildings which hide my tight curves from view.
For those who use the internet, my video for the Guild Spring Show demonstrating track laying for tight radius curves, is still available on the Guild’s YouTube site. Further information can be found on the Guild’s Forum – please search under ‘Jones5669.’ Happy Modelling.
