Easy Z-Probe for Your CNC Router

by tmbarbour

25K460

Intro: Easy Z-Probe for Your CNC Router

Using a cheap dollar-store set of headphones, a couple of alligator clips and a headphone jack, you can add a Z-Probe to your CNC router.

The CNC Router uses a couple of pins for the Z-Probe. When a probe command is issued the router starts moving down (in the Z direction), the pins monitor and when they detect a complete circuit stop the motion.

A set of dollar store headphones work great with an easy mod.

You'll need:

STEP 1: Cut the Earbuds Off the Headphones

Snip off the earbud and throw those away. Carefully strip the insulation back from each wire to reveal two thin wires and some fibers

The wires will normally be colored copper with one side having a blue wire and the other a red one. These wires are thin and delicate and covered with a shellac finish to insulate them.

Carefully snip the fiber filaments away.

STEP 2: Scrape the Insulation Off the Wires

With an Exacto knife on a piece of scrap wood, carefully scrape as much of the colored insulation from each of the wires. You can ignore the copper colored wire. It is not needed and can be cut off.

As you scrape, you should begin to see the shiny copper color come through. You don't have to be perfect. Some insulation is fine and will melt away when you solder the wires.

STEP 3: Attach the Alligator Clips

Add a small piece of shrink tubing to the wires before attaching them to the clips, or splicing them to the alligator leads. This will provide some extra strain relief. Place it right up the end where the insulation was stripped and shrink the tubing.

If you are using the alligator clips by themselves, remove the rubber insulator from the clip and slip it over the wire. I find it easier to remove and reposition the rubber insulators by first snapping the alligator clips to a screwdriver. This reduces the width and makes removing the cover easier.

Place the wire in the alligator clip and insert the bare wire into the hole. Hold the wire in place and crimp the strain relief tabs onto the wire/heat shrink tubing.

STEP 4: Solder the Alligator Clips

Solder the bare wire to the alligator clip.

Clip it to a screwdriver and slide the rubber insulator back over the clip.

STEP 5: If Using Pre-made Alligator Leads

Cut one lead in half. You can use both parts for each side. It does't matter if they'e the same color, there's no polarity.

Strip the lead wire. Place a piece of heat-shrink tubing over the lead wire. Twist the stranded wire and shape into a U-shape. Interlock with the headphone wire and solder together. Move the heat-shrink tubing over the splice and heat to shrink.

STEP 6: Double Check the Connections With Your Multi-meter

The male stereo plug has three sections. The top band is the common wire to each headphone. That is usually the bare wire, the one we snipped off.

One clip will be connected to the middle band, and one the the tip band.

Make sure that the continuity is good for each clip to it's segment.

STEP 7: Build the Headphone Jack Assembly

Snip the ends of a pair of jumper wires and strip the insulation back.

Place a couple of small pieces of heat-shrink tubing over each wire.

Interlock the wires through the bottom-two connectors and solder.

Slide the heat-shrink tubing back and shrink to finish the connection

I've never had a problem, but some have reported issues with spurious probe issues, especially when doing a bed level sequence. To minimize this a capacitor can be added in parallel to the probe circuit. The easiest way would be to solder a capacitor across the two jack terminals when soldering the wires in place.

STEP 8: Mount the Headphone Jack.

Mount the headphone jack to the CNC router frame somewhere convenient. The headphone jack jumpers will connect to the probe pins on the CNC, so the length of the jumper will probably determine the best place to mount it.

You can take a small piece (2" x3") of scrap 1/8" plywood and screw it to the frame as a mounting plate.

I happened to have the Electronics enclosure that I used for my Optical Tachometer.

Drill a hole that is big enough for the headphone jack's threads, but smaller than the console mounting nut that came with it.

Unscrew the nut, insert the headphone jack through the hole and tighten the nut.

STEP 9: Connect the Wires to the Electronics

The probe connects to the SCL and the GND wires on a CNC Shield on the upper right. It doesn't matter which wire connects to which pin.

Connect the jumper wires from the headphone jack to the correct pins.

STEP 10: Test the Probe

Insert the probe plug into the headphone jack. Keep the two alligator clips apart.

Start a probe cycle on your CNC software. Once the tool starts moving down, touch the two alligator clips together. The tool should stop immediately.

If it doesn't:

  • Recheck that your jumpers are connected to the correct pins on the CNC shield.
  • Use your multimeter to check the continuity from the jumper wires to each alligator clip

STEP 11: Create Some Conductive Strips

Take a piece of aluminum duct tape (used for furnace ducts) a few inches long.

Peel the backing off along the side, about 1/3 of the way.

Fold the tape over on itself, and press firmly.

Cut the tape into strips

STEP 12: Use the Conductive Strips With the Probe

Move the tool over the location you would like to probe.

It's best to move the tool down reasonably close to the material. The probe function moves the tool very slowly, so it's faster to get it close yourself

  1. Take a conductive strip and peel off the backing
  2. Press it down on the top of the material. Try to keep any wrinkles or bubbles out. Peel it up and reapply if it didn't go down smoothly.
  3. Clip one alligator clip to the fold on the strip
  4. Clip the other clip to the end mill
  5. Start a probe cycle, the tool should move slowly down until it touches the strip then it should stop.
  6. Zero out your Z coordinate
  7. Move the tool up
  8. Remove the alligator clips, unplug the probe and peel up the conductive strip