Touch Probe

 

Sometimes you buy (or make) a tool or accessory and when you’re done you never figured out how you got along without it.  This is one of those things.

The touch probe is actually a pretty basic thing that gets wired into the computer and simply lets you know when electrical contact is made.  From there the computer does all the magic.

The touch probe tip is broken down into a couple of sections:

  • Basic assembly of the probe

  • Connecting the probe and setting up Mach 2

  • Using the probe (sounds scary doesn’t it?)

  • Making a probe for only a few bucks

 

 
Here is a plain electronic edge-finder.  I paid less than $20 for it.
 
Electronic is a fairly loose term.  A battery, resistor, and a LED make it electronic.

In this picture everything was taken apart and checked for location.  Then reassembled and a 3/16 hole drilled into what would be considered the shank of the device.  The hole goes through the shank and into the center of the plastic LED holder.
 
Take the LED out of the little plastic LED holder and set the parts aside.

Using a short length (12" or so) of multi-conductor remove the individual wires from the jacket without damaging the jacket.
 
Remove the existing resistor, and prepare to attach 2 new resistors.  Trim the leads short as in the top of the picture.
 
Both resistors attached.
 
Now the extension leads attached.  Keep everything really small.
 
Put a small piece of heat shrink tubing over the resistors.
 
Wiggle everything around a pinch and stuff it in the little tube.  you will need to get the two wires out of the hole.

 

If you think the resistor/led setup looks a little different you are correct.  This picture is from the first setup, which didn't work quite the way I had hoped.
 
Now thread the third wire through the hole as well.  The black wire (good color choice as it connects to ground) is just a straight wire at this point, nothing has been done to it.
 
Now stuff all of this into the original body.

 

You might need to shave the plastic near the LED a little to get it all in the shank.
 
Everything stuffed in.

 

The black wire is hanging out the back.
 
The original edge-finder had a battery, that will NOT work here.  While I was at the hardware store I found this little nylon spacer that is exactly the same size.  The little brass disk came with the edge-finder.
 
Run the wire through the spacer and solder it to the brass disk.
 
Gently pull the black wire through and this will draw your new "barrery" into the shank.
 
Screw the back cap back on.

Here is what you should have.  The three wires out of the hole you drilled in it and the saved cable jacket from the earlier step 
 
Run all three wire back through the jacket.

 

This was originally a 4 wire cable, getting 3 of them back through was actually pretty easy.
 
Using some more cable extend the leads to a good length, we chose about 8 feet.
 
Seal the cable with heat shrink tubing.
 
In the next installment I will include a basic schematic and resistor values for both a 5 Volt setup and for connection to a 12 Volt breakout board.  If you decide to just go with the colored bands to figured out what I used please note that I have a 5 Volt setup.