Selectric Resources

 

DOUBLE INDEXING OPERATIONAL THEORY

 

The purpose of the double indexing device is to provide a second index operation for each carrier return operation.

 

Double indexing is performed in the following way. When the carrier return button is depressed, a normal indexing and carrier return operation occurs. Motion from the carrier return shoe bellcrank through the interlock shaft rotates the index trip shaft. The tripper, mounted on the trip shaft, rotates downward, pulling the index keylever pawl down. The index keylever pawl releases the index interposer, causing a second index operation.

 

The double indexing mechanism can be locked out so that normal linespacing will occur. To lock out the double indexing operation, the mode switch, mounted above the ON/OFF switch lever, is rotated toward the front of the machine. The mode lever, through a link and locator, loads the tripper and tripper shaft to the left so the tripper rotates between the index and carrier return keylever pawls when operated. When the tripper rotates between the index and carrier keylever pawls, normal linespacing will occur.

 

This mechanism provides 2, 3, 4 and 6 lines per inch with standard 54-tooth indexing, or 2, 4, and 8 lines per inch with standard 36-tooth indexing for printing and publishing customers with OCR applications.

 

This double index can be installed on all US. “Selectric,” “Selectric” II, and Correcting “Selectric” typewriters, with the exception of machines equipped with the following:

 

1. Manual velocity control

2. Shift sensing

3. Space to print interlock

4. AVC inhibitor

 

Figure 1 — Double Indexing Device.