TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

4. When the key is normal the tip of the spring K1 must be approximately in the
centre of the gap in the wheel and clear the wheel by 0.015 inch minimum.
5. The inner spring when at the bottom of a tooth shall exert a pressure of 10
grams minimum on the wheel and when at the top of a tooth 175 grams
maximum, including the pressure of the outer spring. When at the top of a
tooth the inner spring shall have a pressure of 15 grams minimum exerted
upon it by the outer spring.
6. The nickel silver contact spring shall be adjusted to give a 50/50 make to
break ratio, as previously described. The permissible variation being between
53/47 and 47/53. To give this there should be a clearance of 0.030 inch
minimum 0.034 inch maximum between the inner and outer spring contacts
when the operating spring occupies a midway position between any two
teeth. This dimension is to ensure a good contact gap and also checks the set
of the tip of the steel impulsing spring.
7. When a bent-up segment is used the bent-up portion shall engage the insulator,
on the tip of the outer spring, approximately on either side of the centre
line of the insulator.
Page 23