SETTING DWELL TIMER
The dwell (spark out) on the PG-9B Centerless Form Grinder is the result of
the setting of the dwell timer on the console.
As the ram reaches the end of it's forward grinding movement, the #5 orange
micro-switch is closed by it's mating cam. The signal from this micro-switch
starts the dwell timer.
To accurately position the #5 orange micro-switch cam, permit the ram to
hold in the forward position as you very slowly slide the cam rearward until
it closes the #5 orange micro-switch. This will be evedent by noting the
descending time on the timer.
In actual practice, it is intended that the cam will operate the #5 orange
micro-switch on the last few thousandths of forward motion. It can be seen
therefore, that a few seconds of time to complete the forward movement of
the ram on the ram bed will be a part of the total time set in the dwell
timer.
The length of dwell for any particular part will depend on the tolerance
requirements and the material which is being ground.
A soft material like unfired ceramic will require only a very short dwell. Hard,
crisp materials such as cast phenolics can normally be ground with a nominal
dwell and at the same time hold good tolerances. High impact materials such
as polystyrene will require a long dwell in order to obtain tolerance control.
This would be especially true when grinding balls which might require a tight
sphericity tolerance.
Experimentation will soon indicate the best dwell timer setting.
SETTING DWELL TIMER WITH POSITIVE STOP SCREW MICRO ASSEMBLY
This micro assembly replaces the orange micro described above. The microswitch
within the positive stop screw knob is set at the factory to operate
approximately .010 before the ram reaches the end of it's stroke. Should it
be necessary to readjust the micro, proceed as follows: Remove rear cover
( 4 screws); back off three (3) cone point set screws from the sleeve; pull
micro-switch out of the sleeve (use care not to damage wires). The switch
is threaded into an aluminum bushing and held in place with a locknut.
Loosen locknut and screw micro-switch farther in to start dwell timer earlier;
screw it farther out of the bushing to start dwell timer later. Tighten locknut.
To assemble, reverse above procedure.