Poor Man's CNC Edge Finder

Aluminum foil tape offers a very simple, precise and cheap way to zero almost any workpiece.

Things you need:

• Aluminum foil tape - it can be found at most hardware stores.
• One or two alligator clips.
• A 100nF ceramic capacitor (optional but recommended)
• A CNC controller with sensor assisted edge finding capabilities like Estlcam
  

How it works:

• The aluminum tape and tool act as switch. Once the tool touches the tape the circuit is completed and the probe input of the CNC controller triggers.
• The aluminum tape is connected to the probe input using an alligator clip.
  (Pin D6 for Estlcam / A5 for GRBL)
• The tool is connected to GND
  • I've connected GND to the spindle housing as it is conductive all the way through to the tool.
    (Check this first - not all spindle housings are conductive and connected to the tool.)
  • This way the GND connection can stay permanently and you can even touch off with the spindle running.
• Add a 100nF ceramic capacitor between probe input and GND close to the controller - this suppresses interferences which may trigger the input unintentionally.

Prepare the tape:

• Prefer tape with liner - it is easier to work with.
• Cut a short length of tape from the roll and turn it over.
• Fold the liner back lengthwise to expose the upper half of the glued aluminum foil.
• Then fold about 5mm (1/4") of the tape itself down and put the liner back.
• Finally cut the tape into short stripes.

Advantages:

• Ready to use strips.
• Liner can be removed easily.
• Folded back part of the tape does not keep sticking to the alligator clip.

You'll find most information in the video at the beginning - so just a few final thoughts:

• The tape can be reused several times. The wrinkles add some thickness and therefore error but for most applications this should be insignificant (I've measured a difference of 0.02mm / 0.0008" between new and badly wrinkled tape)
• This also works for conductive workpieces with a small modification, even if the machine bed and workpiece is connected to GND. Just put regular tape below the aluminum tape to add an isolation layer.
• Be careful with coated tools. Some coatings are non-conductive so the circuit will not close -> risk of breaking the tool. If in doubt check the tool with a multimeter first.