904 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



10. The lower shear blade is moved upward, shearing off the tapes. 



11. The upper shear blade is raised and the welded comb is transferred 

 either to the second similar welder head or to the next operation. 



The upper electrode tips are pins of special electrode material fixed 

 in the ends of the supporting cantilever spring members by tapered 

 joints, Fig. 5. Each electrode member is insulated electrically from the 

 others and from ground by a coating of Teflon and a slotted phenol 

 fibre guide block (not shown in Fig. 5) at the end adjacent to the elec- 

 trode tips. Teflon furnishes the necessary insulation in a minimum of 

 space and is slippery enough to allow free movement of any member. 

 The cantilever construction makes a very light electrode assembly ^^^th 

 the quick follow through necessary to maintain pressure on the weld 

 area as the projection on the palladium tape is melted during the short 

 weld cycle. A deflection of one-sixteenth inch at the tips vdW produce a 

 force of about ten pounds, which is ample for this welding job. The 

 working surfaces of the electrode tips are dressed approximately every 

 20,000 parts by an abrasive wheel mounted on an arbor and rotated 

 back and forth by hand with the electrode tips pressed against the fiat 

 side of the wheel. In this manner all electrodes are dressed to a uniform 

 length and angle simultaneously. After repeated dressings have reduced 

 the tip length by approximately one-eighth inch, new tips are inserted. 



MECHANICS OF THE WELDER 



The w'elder is driven by an electric motor connected to the main cam 

 shaft through a suitable reduction gear. This cam shaft is located just 

 under the table top and extends the length of the machine. A me- 

 chanical overload clutch is provided on the output shaft of the reduction 

 gear. All cams for the head movements are located on the main shaft. 

 A solenoid operated clutch stops the main cam shaft when necessary. 

 When no comb is in the weld position the weld control circuit is held 

 open and solenoids shift either of the tape feed cams axially out of line 

 with their followers to prevent the feeding of tape. This prevents burning 

 the electrodes, saves precious metal and avoids loose contact pieces 

 which might interfere \^^th succeeding welds. A reciprocating conveyor, 

 extending through the machine about four inches above the table top, 

 carries the combs through the two weld positions. Excessive load, as 

 when a part jams, mil trip a microswitch and stop the machine. 



TAPE SUPPLY 



The contact tapes are advanced the amount required to provide the 

 exact contact lengths by means of opposing rubber-faced feed rolls in 



