"N Cook" wrote in message
...

| I will dig out such a book from the loft.
| Inductance measurements on the commutator
| are 180mH per diameter and
| 2.9,1.6,.4,.4,1.6,2.9 mH for 3 contacts either side
| of any given contact so no cold shorts anyway.
| I don't see what physical mechanism could cause one land to be
| 7 thou (mil) proud of the others. Also while still in use, why the brushes
| weren't ground down to nothing with that sort of irregularity.
| Has localised heating caused the copper of that land to somehow
permanently
| expand by carbon incorporating into the copper ?

The best idea I can come up with was that this was made on a Monday and got
through whatever QC they have, unless it was a factory reject. Disturbing.

N