Cheap and easy spindle index sensor for G540 and Mach 3

[grizzlymog]

Here's some details of a spindle index sensor I'm using on my smithy cnc retrofit project. I have a couple of inductive proximity sensors (http://www.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Inductive_Proximity_Sensors/18mm_Round_(AK-z-VK1-z-PKW_Series)/Extended_Sensing_Distance_(AK1_Series)/AK1-AN-3H) on my plasma cutting gantry and figured one would make a good spindle index sensor. I've used these for years and they are super tough, surviving heat, molten metal spatter, and splashing from the water table. I found they work great as a spindle index sensor too. At 18mm dia. they are a bit large, but smaller, 12 and 8mm sensors are available.

Mach 3 likes one index pulse per rev to index the spindle rpm. I epoxied a short piece of light gauge steel angle to the back of my spindle pulley for the trigger, and mounted the sensor a few mm away so that it would sense the trigger and not the pulley (see pic). The sensor has a built-in LED which helps in adjusting the gap distance.

The wiring is straightforward. I used a 12v wall power supply to power the sensor which likes 10-30 VDC. I used a multimeter to identify the lead polarity, then connected (-) to G540 pin 12, (+) to sensor positive, and NO sensor output to G540 pin 1 (see diagram).

I tested the RPM seen by Mach with a cheapo laser tachometer and the results were identical over the full range of my lathe pulley combinations (~169-2124 rpm).

The cost of a new sensor is ~$25 and doesn't require any add-on encoder/decoder cards or slotted plates, just a small piece of scrap and some epoxy and you're good to go.

[Sam]

Thanks for sharing your methods. Don't forget about the sensor cable. If memory serves correct, I think there about as much as the sensor.

[grizzlymog]

Doh! Sorry about that, forgot about cabling since I had these things lying around the shop already. Cabling with one female quick disconnect runs ~$4-5 per meter.  The connectors are well worth the small added cost. I've dunked these sensors a number of times on the water table and they are apparently water tight. If you are using these things in a lathe/milling environment then you don't have to worry about coolant, etc. They have been impervious in a plasma cutting environment where - along with heat, jarring, submersion, and RF - are exposed to the dreaded fine magnetic dust, and they just perform. These are a rugged sensor/cable for a shop environment.

Thanks for sharing your methods. Don't forget about the sensor cable. If memory serves correct, I think there about as much as the sensor.

[Kerry Harrison]

Wow this sure seems like a great spindle sensor.

Could you explain how this would be wired to a breakout board please?

Also could these be used for limit/homing switches?

Thanks much,
Kerry