The interrupter disc is made of 0.04" aluminum and has a 27mm spindle mounting hole and an outside diameter of 57mm. Please note that the two small round holes serve no purpose -- they were used to secure the part during manufacture.

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The disc is shown mounted on the spindle of my Grizzly 7x12. You can see the opto-interrupter mounted on a small aluminum bracket that is held to the lathe by the hex cap screw in the upper left of the picture. I used two #6-32 cap screws to hold the opto-interrupter to the bracket. The screws almost self-tapped into the plastic sensor housing, but I ran a tap through just to make sure it wouldn't split. The blue stuff is heat shrink tubing that is covering the two resistors and the cable connections to the opto-interrupter. Under that blue heat shrink are smaller pieces of heat shrink covering the individual connections and resistors, so nothing shorts together. The gap on the opto-interrupter straddles the interrupter disc and creates a pulse every time the slot in the disc runs through the gap, when properly wired. There is an infrared emitting LED on one side of the gap and an infrared detecting phototransistor on the other side. The cable requires just three conductors; one for +5V, one for ground and one for the sensor output signal. The cable I used has a shield conductor which I used for the signal ground. This should help shield the signal from external electrical noise. Be very careful that this signal ground is isolated from the lathe frame which is connected to the AC mains ground.

See the schematic for the sensor wiring below.

You may contact me by email: probe (at) tetralite (dot) com