Just when I thought that all was going well and looking forward to a day of progress. I sat down at the bench to complete the task of cutting the new recesses, for the vac-cyl. and cross-shaft etch, in the resin floor mouldings and looked at the most recent drawings from Dave... an official drawing of a welded angle underframe. Why did I do this? Because I wished to see how Dave's drawing differed to Mike's drawing (an early post to this topic) in the area of the diagonals of the central cross-girders.
And now I wish that I had not for that vac-cyl. seems to have moved again.
A comparison of photographs which show the side views of the "standard" 61' 6" Gresley carriages reveals that the location of the vac-cyl. is not fixed and that the vac-cyl. position seems to be related to the style of underframe (truss-rod / angle) and possibly to the construction method (riveted/welded). Mike Trice has provided a copy of an official welded angle underframe drawing and comparing that drawing with the equivalent for a truss-rod underframe (MJT) confirms that the vac-cyl. is closer to the centre of a welded underframe than the equivalent of a truss-rod underframe. Dimensions, for the distance between the centre of the vac-cyl. trunnion and the centre of the coach, from those drawings are:-
[1] truss-rod - 5' 0" + 4' 10 1/2" + 1' 10 1/2" giving 11' 9" at the dynamo end;
[2] truss-rod - 5' 0" + 5' 3 3/8" + 1' 10 1/2" giving 12' 1 7/8"at the non-dynamo end;
[3] welded angle - 4' 9 1/8" + 8' 5 3/8" - 2' 3 1/2" giving 10' 11 3/8" at each end.
A copy of an official truss-rod underframe drawing, that has been provided by Dave, aligns with the MJT information
. As I am not building any truss-rod underframes I was not initially concerned about [1] and [2] above.... although I think that Rob Pulham might be interested as he is doing truss-rod underframes. Mike - can you confirm that the reason for the difference between [1] and [2] is that the greater dimension of [2] allows more room for the handbrake levers of a brake carriage?
Dave has forwarded this past week (thank you Dave) an official welded angle underframe drawing and that drawing has dfferences, in the diagonal braces to the central girders, to the official welded angle drawing from Mike. Using the same criteria as for the truss-rod comparison above, the results for the two welded angle drawings are:-
[3] welded angle (Mike) - 4' 9 1/8" + 8' 5 3/8" - 2' 3 1/2" giving 10' 11 3/8" at each end;
[4] welded angle (Dave) - 4' 9" + 4' 1" + 1' 10 1/2" giving 10' 8 1/2" at each end.
(the two drawings are not dimensioned in the same way hence the difference in the calculations)
Now I am confused
for I cannot see a reason why the vac-cyl. is in different locations on the angle drawings. More to the point, given what I set out to do today, I am stumped as to which dimension to use when cutting the new recesses.... and as there are two recessed per floor and at least four floors then I could be about to make a big blunder
To Mike and Dave - what are the dates of your respective drawings? When is the earliest date that underframes to those drawings would been used in the new construction? What type of carriages might have used underframes to those drawings?
Thank you, Graham (who is going off to modify the supplied vac-cyl castings to be closer to what is visible in the photos from Mike, Dave and Jonpaul).
. A pity that there are 205 miles give or take a tad between the respective workbenches so we shall have to rely on t'internet to keep going in the correct direction (and without the "brakes on" 
).
