Original text of illustration:

Figure 249: Modern form of the Gramme ring armature.

• The core consists of a number of thin flat rings of well-annealed charcoal iron, the outer diameter of each ring or disc being 11.5 inches and its inner diameter 9.25 inches. Sheets of thin paper insulate each disc from its neighbors to prevent the flow of eddy currents.
• The armature is mounted on a steel shaft to which is keyed a four-armed metal "spider", the extremes of whose arms fit into notches cut in the inner edges of the soft iron core rings, so that a good mechanical connection is obtained between the core and the shaft. The spider is made of a non-magnetic metal, to reduce the tendency to leakage of lines of force across the interior of the armature.
• The armature inductors consist of cotton-covered copper wire of No. 9 standard wire gauge, wound around the core in one layer and offering a resistance, from brush to brush, of 0.048 ohm. There are two convolutions in each section, the adjacent ends of neighboring sections being soldered to radial lugs projecting from the commutator bars.

Public Domain source:

• Hawkins Electrical Guide, Volume 1
• Chapter 17: The Armature, Page 224.
• Copyright 1917 by Theo. Audel & Co.
• Printed in the United States

Scanned by Dale Mahalko, Gilman, WI, USA