Carriage underframes - why does the dynamo position move?

[gdb]

In building a D114 from the JLTRT kit I came to the conclusion that the dynamo trimmer on the supplied underframe moulding was at the wrong end of the coach... the kit puts the dynamo at the brake end whereas the LNER diagram for D114 (and photos in Harris) put the dynamo at the non-brake end. Fine, need to put a new trimmer into the underframe at the non-brake end.

Not so easy.... consult the MJT underframe drawing (from Dart Castings) and that gives the location of the required trimmer, from that drawing the JLTRT moulding appears to have the correct distance between trimmer and truss girder beam - just the wrong cross-girder. Thought I would check on the LNER angle-iron drawing which Mike Trice sent to me.... and on that drawing the dynamo trimmer is about 12" further away from the cross-girder (closer to the adjacent bogie). Guess who wants a D114 with an angle-iron underframe?

When the underframe changed from truss-rod to angle-iron, was the angle-iron underframe "rivetted"? I ask because the LNER drawing which Mike provided is marked as "welded". If there was an earlier version of the angle-iron underframe then was the trimmer placed as per the truss rod version or as the welded version? (the angle-iron drawing which I received from Mike has no date or number, Mike has suggested that the drawing might be 15012.D dated 15/2/1934)



I appreciate that the dynamo is suspended from a bracket which has pivots at top and bottom... so maybe changing the location of the dynamo trimmer changes the way in which the bracket lies relative to the underframe rather than moving the axis of the dynamo relative to the bogie.... can anyone throw any light on this puzzle before I fix a new trimmer into the model underframe?

regards and thank you, Graham Beare

[Dave]

Graham

Just seen this item....did you get any info...if not let me know I might have somthing that helps..

[gdb]

Graham

Just seen this item....did you get any info...if not let me know I might have somthing that helps..

Well not quite although Mike Trice has forwarded some LNER drawings which show how the dynamo was suspended from the underframe.

So although the thread has been quiet there has been some resolution - I was partly correct and definitely wrong in my analysis of the information which was available at the time I posted the topic. Since that time I have made a sketch of the relationship between vac-cyl., cross-shaft and dynamo trimmer, which with scale dimensions allows me to make a sensible assessment of the JLTRT underframe... and then decide just what is ok and what is not. What surprised me is that the dynamo trimmer does not move relative to the cross-members of the prototype... it seems to be the vacuum cylinder and associated cross-shaft which changes location between truss-rod and angle-iron designs.

Accepting that the truss-rod drawing and the angle-iron drawing record the locations of some items in different ways, and that the reference points do not necessarily align between the two drawings (referencepoint appears to be centre of truss-rod cross girder and an edge of the angle-iron equivalent), I have come to the following conclusions about the JLTRT undeframe:-
[1] the kit has the cross-girders in the correct places for truss-rod and angle-iron underframes;
[2] the dynamo trimmer is in the correct place for truss-rod and angle-iron underframes;
[3] the vacuum cylinder and cross-shaft are about 80 thou too high in the underframe, (solebar hides the trunnions);
[4] the vacuum cylinder and cross-shaft are too far from the central girders for an angle-iron underframe.

Note that the JLTRT kit for the D115 has the dynamo trimmer in the correct place whereas the kit for the D114 has the dynamo trimmer under the brake end- so a new trimmer is required for thr D114 kit.

thank you and regards, Graham