Originally Posted by Tin Falcon
This may be a realy dumb question but how is contact made inside . I am not quite seeing how this works.
There are no dumb questions, if 1 person is asking then 20 other people are thinking it.
There are no contacts inside. The Teflon tape forms an insulator between the two wires and the metal they are attached to. The electricity requires another path to flow and make the buzzer sound. This other path is the body of the mill or lathe itself.
The contact is made (or for a normal circuit the switch is closed) by the cutter or tool tip through the machine body. (mill or lathe)
When the cutter touches the top button of the zero setter the circuit is completed and the buzzer sounds, without the cutter touching the zero setter the circuit is open and the buzzer is silent.
The path the electrical current takes from the battery is through the red wire to the top button of the zero setter, from there it flows through the cutter and machine body to the machine table and part to be machined.
It then flows through the zero setter base to the button holder and back through the black wire (note below
) to the buzzers red wire, from the buzzer it flows back to the battery in the black wire.
So in effect there is no moving contact inside the zero setter. The only moving part is the spring and its only job is to absorb the pressure of the cutter touching down too hard.
The correct offset reading is taken when the buzzer just starts to sound on application of the cutter.
If the spring has been compressed by the cutter touching down too hard, the the reading is taken when the buzzer stops sounding on withdrawal of the cutter.Note:
If you're machining a non-conductive material like PTFE of PVC the the current can not flow back through the part being machined. to get around this I mounted my buzzer and battery in a metal box (jiffy box) and connected an extra wire to the point where the black wire from the button holder and the buzzers red wire are connected. Then I connected that extra wire the the metal box. So as long the metal box is resting on the machines metal surface somewhere then there is a return part for the current to flow.
Sorry for the long winded reply, I hope I've covered it.
ps the above explanation assumes conventional current flow theory as opposed to electron flow theory.