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Each tonewheel is a disc of soft iron with a diameter of approximately 2 inches. The rim of the disc is "hobbed" or cut with a specific number of smooth, rounded bumps or "teeth". As the disc rotates, this alternation of the radius leads to a modulation of the magnetic field of the Magnet and Coil pickup. This induces an alternating voltage in the coil of the pickup. There are 96 tonewheels in the generator of most Hammonds, however, some tonewheels are blank and included only to balance the geartrain.

The shape of tonewheel teeth are generally designed to produce a pure sine wave. However, the lowest octave of tonewheels in late model organs do not produce a sine wave. This octave is used only in the pedals. With only two Drawbars to control the pedal waveform, the pedal tones in early Hammonds (A, B-1 & B-2, etc.) sounded a bit dull. In the most popular model Hammonds (B-3, C-3, etc.) the tonewheels of this octave are cut with a more complex pattern to improve the sound (See Complex Tone Wheels).

While each output above the first octave of the Tone Generator should be a pure sine wave, there is some distortion:

The number of bumps or "teeth" on a tonewheel is 2, 4, 8, 16, 32, 64, 128, and as an exception of the power of 2 series, 192. Each successive change in the number of teeth in octaves 1-6 represents a change of one octave:

Octave  No. of Teeth  Frequency  Note Range
  0          2         1 - 12     C0 - B0
  1          4        13 - 24     C1 - B1
  2          8        25 - 36     C2 - B2
  3         16        37 - 48     C3 - B3
  4         32        49 - 60     C4 - B4
  5         64        61 - 72     C5 - B5
  6        128        73 - 84     C6 - B6
  7        192        85 - 91     C7 - F#7


In the most popular models of the Hammond organ, the highest octave is limited to the first 7 tonewheels of 192 teeth. These tonewheels use 192 teeth instead of 256 because the machinery used to cut the tonewheels could not cut 256 bumps in a diameter of only 2". That makes these 7 pitches slightly out of tune (averaging 1.64 cents sharp) from the octaves below because the gear ratios are not precisely correct.

In most Hammonds, the last 5 tonewheels of the upper octave are not cut, have no pickups and are included only for mechanical balance. In spinet organs, such as the M-series, the first 5 tonewheels of the second octave are also not cut, have no pickups and are included only for mechanical balance. Since the range of the lower manual on spinet organs stops at F, tonewheels C1 through E1 are not needed.

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