5" Britannia Drawings

[baggo]

Hi All,

Some time ago I picked up a set of s/h drawings for a 5" Brit but I don't know who produced them or the castings mentioned on the individual sheets. The drawings consist of 10 sheets labelled Plan 1 to Plan 10 but not sure if there should be any more. The drawings are fairly basic but seem to cover all the details. The only reference I can find which may give a clue is on sheet 10 which says drawn by T J Adlington - 12/6/69. Anybody any ideas?

John

[bobfly]

T J ADLINGTON was a member of the Glasgow S M E, the castings were probably done by WILWAUGH who was also a member of the same club.The loco won a championship cup at one of the Glagow model exibitions, it certainly went well do not know of the whereabouts of the loco now.

[baggo]

Hi Bobfly,

Thanks for that info. I looked back through ME and found an 'Around the Trade' feature which shows photos of a 5" Brit built by James Perrier using the Wilwau castings. It would appear that the business was taken over by Norman Spink in 1972. I've seen reference to a 'Perrier' design Brit but did he produce his own drawings or use/copy the Adlington ones I wonder.

John

[waggy]

Perrier is recorded as drawing up his version from works drawings, as he did with his King.

Norman Spink did supply castings until he passed on, his business was taken over by Blackgates. (I have no connection to either party, info, only.)

Waggy.

[Deleted]

Hi John,

Could you possibly give me the measurements from these drawings for the length of the eccentric rod between bearing centres, and the throw of the return crank? My Modelworks kit has a problem with these parts which causes the top of the expansion link to hit the weighshaft at the rear of its travel, and Modelworks are apparently going to replace the eccentric rod and return crank to resolve this. I'd be interested to know how these measurements compare.

Regards, John

[baggo]

Thanks Waggy,
I thought Perrier may have done his own drawings as the photos of his Brit show a lot more scale detail than the drawings I have.


John:
The length of the eccentric rods (centre to centre) is given as approx. 5-1/2". Presumably the exact length would be measured from the actual job.

The return crank has a centre to centre distance of 1-3/8". The radius of the return crank pitch circle (distance of centre of return crank pin from the axle centre) is not stated but by scaling from the drawing I get it to be approx. 5/8". The actual return crank pitch circle diameter can be calculated from the formula

PC = VT x E (from Locomotive Valve Gears by Martin Evans)
............L

where VT = valve travel, L = radius of centre of expansion link die at full travel, E = distance of centre of expansion link drive pin from centreline of expansion link pivot.




Hope that helps,

John

[Deleted]

John,

Thanks for the measurements - the three figures that you quote agree pretty exactly with my existing return crank and eccentric rod, so I'm puzzled now as to where the problem is! I'll have to wait and see what Modelworks come up with.

Regards, John

[baggo]

Hi John,

Looking at the photo of the valve gear on your site, the bottom of the expansion link does seem to be angled too far forward for the position of the return crank which would suggest that the eccentric rod may be too long. Everything else looks pretty much like my drawings. As you say, see what Modelworks come up with.

John

[Deleted]

John,

I've now got the replacement eccentric rods and return cranks from Modelworks. The eccentric rod is 3mm shorter at 135mm or 5 5/16" and the return crank pitch circle is slightly reduced at about 31mm or 1 7/32". Everything looks spot on in full forward gear, but in neutral or reverse the valve crosshead is 1 or 2mm forward of the central position and I think this is because the entire weighshaft bracket and expansion link bearing assembly is 1 or 2mm forward of the correct position (which makes little difference in forward gear, when the radius rod is more or less in line with the eccentric rod). It should be simple enough to ease the bracket fixing holes in the frames to correct this, although I'll check with Modelworks first to see if their control model is the same.

Regards, John

[baggo]

Hi John,

Glad you're getting there! As you suggest, the mid gear/reverse problem could well be caused by the expansion link bearings being in the wrong position. As a matter of interest, on my drawings the position of the centre of the expansion link bearing is 5-5/8" from the driving axle centre and 1-7/8" above.

I must admit that I find it rather disconcerting that the sort of problems that you are having can actually happen. Surely major problems such as incorrect valve gear parts should have been spotted on the control model? All credit to Modelworks for their help and support but at the end of the day it shouldn't be happening in the first place.

Regards,

John