BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

I was asked to go and get a full-width half-shaft.

 

We used to send the kids to someone else's lab for "the long stand".
Ray.

 

A Stratford apprentice got sent to the stores for a sack of 3/4" holes, brought back a sack of washers, with the explanation that they were out of holes, but if You* file the outsides off of these they'll do the same job.



* Not referring to any fellow posters of a different political outlook to Myself.

 

Yep, i was sent off to get a can of grinding sparks...

 

To return to the day job.......

We are carefully checking the fit of the outer race of the bearings in the bogie cannon axleboxes. One cannon box is OK; the other is a little bit tight so some careful easing is going on. Once we are happy with this, we can get the inside of the cannon boxes painted with 2 pack, oil resistant paint. All other components are ready to be shipped to South Devon Railway Engineering.

Another area getting careful attention is the fitting of the frame plates to the central bogie stretcher. Again this is a fitting job to ensure that the machining top face of the frame plates sit tightly against the corresponding machined face on the stretcher.

We've added 2 new pages to the design section of the web site. The first discusses the 3 types of dragbox that were designed for the Class 6 Clans (4 if you are being very picky!)

https://www.theclanproject.org/design/Clan_Dragbox.php

The second discusses axlebox lubrication

https://www.theclanproject.org/design/Clan_Axleboxes.php

Hope you find them interesting

Ian

 

Does this mean that you will need to remove the dragbox from the loco (I assume for scrap, unless it can be modified to the MK3 design?) and build a new one? Has it ever been noted if 71000 or either of the Britannias have experienced any oscillating in preservation use with the MK3 dragbox?

 

We're fortunate both surviving 'Brits' were among locos so fitted, that late in the day. One aspect of this is that, given the comments concerning the lack of any issues with 71000, it would appear to vindicate Bulleid's views on 3 cylinders and balanced axles.

 

The existing dragbox will have to be scrapped. We've investigated and its not cost effective to modify. We do not believe that 71000 suffers from oscillation as it is a 3 cylinder engine. We know that 70000 does still suffer from oscillation. We have provided a copy of SL/SW/1544 Special Maintenance Instructions - Intermediate Draw Gear which provides a set of detailed measurements for setting up the locomotive and tender. We also want to look into the Spencer Moulton drawbar springs - the LSSC meetings refer to a number of different part numbers - presumably with different qualities of rubber (?) to provide different damping conditions. Other items mentioned in the meeting minutes

1. Intermediate buffers on front of tenders - the BR1F tender spring has more coils than the one fitted to the BR1 tender
2. The setting up of the tender drawhook - again a Spencer Moulton drawbar spring is used and a different rating is used for the BR1F tender (more water so heavier)
3. In one case, the minutes record that the couplings between the first and second coaches had not been set up properly and this was causing oscillation

 

Your Mk1 dragbox is a myth. The drawbar is pinned in the loco dragbox SL/DE 19619 and the spencer moulton spring gear is in the tender dragbox. Have a look at the drawing for the intermediate drawgear on a Bulleid pacific.

 

As both the RCTS book and Harvey talk about the drawbar spring and Harvey says "as used on many LNER locomotives", I had assumed that the drawbar spring was on the loco. However the Mk 1 drawbar drawing shows the nut on the right and, generally, left is front on the drawings. I've checked the loco dragbox drawing and the issue date is 4/5/1950. Perhaps we should refer to Mark 1 drawbar system instead. The tender dragbox must have been changed as there is nowhere obvious for a drawbar spring to bear against on SL/DE/20770.

The first BR1 tender front dragbox drawing in the NRM list is SL/DE/20300 initial date 24/9/50. There is another BR1 front dragbox drawing SL/DE/20770 dated 5/9/51 which is 3 months after the GE trials that identified the problem.

 

The web page has been modified to refer to the "drawbar system" instead

 

Yes, the front dragbox to drawing SL/DE 20300 was extensively modified to accommodate the solid drawbar and retaining pin, dated August 1951. Dragboxes to SL/DF 20770 were used for later batches of BR1 tenders and other various Standard tenders.

 

It would be quite unusual with 71000 since it is a three cylinder machine. In the USA they used to balance locomotives with a driving wheel diameter which was less than that of the Britannia class up to speeds well in excess of 100 mph. Using the tender drawgear to compensate for and absorb the deficiencies of balance fitted to the locomotive does not appear to be a satisfactory way of doing things.

 

I do not understand all the detail of the recent discussion of drawbar systems, but it does seem that BR went through a series of designs without ever entirely curing a problem. Why not look at other designs from the Big 4's many express and mixed traffic classes? This Clan is intended to be a "new improved" version of the originals with a number of other changes, so why not look as widely as possible at alternative drawbar systems? (And, vide post#2433, rethink the balancing as well.)

 

Apart from the GW County and47xx I cannot think of any British 2 cylinder loco above class 5 that did Express Passenger work. Maybe looking beyond these shores is an idea...

 

Surely,Britannias fit this category.

 

None of the Big Four had large, two cylinder express engines, with the possible exception of the GWR Counties, and multi-cylinder engines did not generate the offset thrusts set out in the 72010 report. Nor did any have the frames inset to be above the centres of the axleboxes except the Bulleid Pacifics, which had three cylinders anyway, so the Big Four didn't experience the problem, nor have a need to develop s drawbar system which would damp out the vibrations.

 

Let's start with the 9Fs and work backwards. 92220 Cardiff - Paddington and back.

 

True enough but it wasn't just express types which experienced this oscillation. The S & D 7f could bring the coal down when engaged in passenger and they won't have been the only ones. The obsession with two cylinder simplicity can deliver some very undesirable bonuses.

 

Probably the worst example was the WD 2-8-0. But goods engines generally ran at low speeds, and no-one worried if the coal was having an uncomfortable ride.