From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Specification for the inspection and test of an N.B. type dynamo with a 28 slot armature.
| Identifier | ExFiles\Box 70\4\ scan0100 | |
| Date | 19th December 1928 | |
| 19.12.28. R.R. EAC. DYNAMO OF THE N.B. TYPE WITH 28 SLOT ARMATURE. SPECIFICATION OF INSPECTION AND TEST. VERSION 7. Applicable to normal output dynamos with 28 slot armatures, and S.S. type dynamos. Upon receipt of the machine from the assembling benches :- (1) Inspect the brush mechanism and make sure that (a) All brushes have the necessary freedom, without being unduly slack, i.e. there should be .002" to .009" clearance between brush and holder, and that the spring pressures are suitable. The actual pressures exerted by the springs on the main brushes should be 10 ozs.±2ozs. and on the control brushes 8 ozs.±2ozs. Note that for S.S. type machines, the bevels of the brushes slope in the opposite direction from standard machines. (b) The lower edges of the brush holders (near the commutator) are at the same distance of .031±.010 from the surface of the commutator. -5 (c) That corresponding tips of the main brushes are on the average exactly 14 commutator segments apart, and at the same time, the distance of the trailing edge of the control brush from the leading edge of the main positive brush should be nominally on the average 1¾ segments. (d) The brush springs are clear of the sides of the slots of the brush holders, so that the full tensions of the springs are exerted on their respective brushes. Also that these springs are long enough to reach and press on the centre of the brush, and not on the side. Test the springs for cracks, by forcing these back as far as possible, when they should not become cracked. Note (1) It is possible that a spring which is noticeably weak is cracked and requires replacing. Note (2) It will usually be found that a spring which is good has a uniformly expanding spiral. | ||