In staking on the balance, care should be observed to set the banking pin in the rim so it will come right; this is usually secured by setting said pin so it stands opposite to the opening in the half shell.  The seat of the balance on the collet D should be undercut so that there is only an edge to rivet down on the balance.  This will be better understood by inspecting Fig. 181, where we show a vertical section of the collet D and cylinder A.  At g g is shown the undercut edge of the balance seat, which is folded over as the balance is rivetted fast.

About all that remains now to be done is to true up the balance and bring it to poise.  The practice frequently adopted to poise a plain balance is to file it with a half-round file on the inside, in order not to show any detraction when looking at the outer edge of the rim.  A better and quicker plan is to place the balance in a split chuck, and with a diamond or round-pointed tool scoop out a little piece of metal as the balance revolves.  In doing this, the spindle of the lathe is turned by the hand grasping the pulley between the finger and thumb.  The so-called diamond and round-pointed tools are shown at o o’, Fig. 182.  The idea of this plan of reducing the weight of a balance is, one of the tools o is rested on the T-rest and pressed forward until a chip is started and allowed to enter until sufficient metal is engaged, then, by swinging down on the handle of the tool, the chip is taken out.

[Illustration:  Fig. 182]

[Illustration:  Fig. 183]

In placing a balance in a step chuck, the banking pin is caused to enter one of the three slots in the chuck, so as not to be bent down on to the rim of the balance.  It is seldom the depth between the cylinder and escape wheel will need be changed after putting in a new cylinder; if such is the case, however, move the chariot—­we mean the cock attached to the lower plate.  Do not attempt to change the depth by manipulating the balance cock.  Fig. 183 shows, at h h, the form of chip taken out by the tool o o’, Fig. 182.

INDEX

  A

  Acid frosting, 46

  “Action” drawings, 90

  Action of a chronometer escapement, 142

  Acting surface of entrance lip, 127

  Actions of cylinder escapement, 112

  Adhesion of parallel surfaces, 94

  Adjustable pallets, 98

  Adjusting screw for drawing instruments, 21

  Analysis of principles involved in detent, 137

  Analysis of the action of a lever escapement, 86

  Angle-measuring device, 68

  Angular extent of shell of cylinder, 122

  Angular motion, drawing an escapement to show, 91
    How measured, 69
    Of escape wheel, 37

  Antagonistic influences, 133

  Arc of degrees, 9