Probee - A Contact Probe

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Probee - A contact probe for non-conductive materials

Probee is a tool for the Shapeoko 3 as an alternative to a electrical contact probe. Probee creates "contact" by closing a switch. ProbeeBoards.jpg

Design considerations for Probee

  • Functions with SO3 probe connection;
  • Inexpensive;
  • Easy to attach and remove, i.e. not permanently attached;
  • Repeatable measurement;
  • Quick to build;
  • 3D printer unavailable
  • Not designed to perform "touch probing" for 3D rendering.


Probee consists of:

Tools required to build and test Probee:

  • Continuity tester
  • Wire cutters and strippers;
  • Wire pin clamping tool;
  • Solder, Soldering iron
  • Glue, preferred epoxy;
  • Drill and drill bits
  • Wood finishing tools and products, if desired

Make the Probee

1. Cut out the Board

The layout of Probee was completed with Vectric Aspire. The G code in millimeters and inches is available by clicking. The X and Y zero point is at the center of the lower magnet. Z is set to zero at the top of the material being cut. A quarter inch diameter end mill must be used to cut the material. 1/4" plywood is the suggested material, but anything close to 1/4" thick that isn't likely to warp can be used.

2. Wire up Limit Switch

The limit switch used in the prototype has three connection points. Solder the wire to the terminals listed as normally open. Once the ends are soldered, check the ends of the wire for continuity. When the lever on the switch is not pushed, there is no connection. When lever is pushed beyond the "click", the wires will be connected.

3. Connectors to the SO3 controller board

The connectors require two components: The plastic housing; and The metal contact.

The wire from the limit switch is crimped into the metal contact with a special crimping tool and pushed into the plastic housing. I did not use these specific products, but found comparable parts at my local electronic store.

4. Drill the Switch Mounting Holes

Placing the switch on the board, drive a nail or ice pick thru the switches mounting holes to mark the board. Note the switch on the prototype was not mounted level. The switch was mounted with the arm twisted downward. Drill the board, then test mount the switch. Remove the switch. ProbeeInstalled.jpg

5. Prepare Wooden Dowel

The dowel extends a few millimeters, less than 2, to provide alignment of the Probee to the Z axis plate. The 1/4" dowel must be reduced in diameter to just under 5.5 millimeters. Once glued into the Probee board, the dowels and be cut to the correct length.

6. Glue in the Magnets and the Dowels

Although small, these magnets are powerful. Keep away from children and pets. Using wood sticks and epoxy, glue the magnets into the board. The dowels can be glued in at this time as well.

7. Complete the Board

If desired, finish the board. Keep the finish out of the magnet and dowel holes. Sometimes the finish can retard the adhesion of glues. Remount the limit switch. Admire your work. Take a picture and share your success.

Testing the Probee

Learn Some G Code

The Auto Level process makes use of the G38.2 command as well as the initial testing of Probee. For the truly G-code geek the description from NIST, National Institute of Standards and Technology, provides a very complete description. NIST pdf document, PDF page 34, document page 26

Simple Description of the G38.2 Command

Move probe in the axis specified, stop on contact. If no contact is made before the position specified, signal an error.

Example command: g38.2 z-6 f5

Description: The G38.2 command moves the probe in the Z axis toward the location of -6 at a feed rate of 5. If contact is made (the switch on the Probee board closing), the Z motion halts. If the probe reaches the Z location of -6, the Z motion stops and an error is issued.

Minor side note: The probe must move a small amount before the switch is closed or an error is generated.

Put the Probee on the Z Plate

Size the dowels so the magnets hold the board against the Z axis plate. Place the board on the Z axis plate. Connect the Probee to the "Probe" connection of the controller board. PDF file with image of the controller board. Note that the controller board is mounted upside down compared to the image in the PDF file. ControlBoard.jpg

The Molex connector that slides onto the pins on the controller board should be placed so it doesn't click into place. The smooth side of the Molex connector goes toward the plastic clip on the controller board. This will make it easy to remove.

First Probee Test

Be sure the homing sequence has been run before starting this test.

Move the Z axis such that the lever of the Probee switch just touches the material. Set Z to zero.

Move the Z axis up close to the top. Get a pencil or a dowel rod. Have it handy.

Issue this G38.2 command: g38.2 z0 f5 (metric feed rate, slow feed rate)

The Z axis will slowly move down. When SAFE, use the pencil to push to switch lever to trip the Probee switch.

If the SO3 stops its downward motion, it is time to celebrate. If the SO3 continues down, the SO3 will stop at Z equals 0.0. A probe error will be generated however. Check the probe connection plug. Check the wiring for a loose connection. Check the switch again for a change of state.

In bCNC, the probe error can be cleared by clicking on "Reset" then "Unlock". The SO3 will not loose the coordinate location in bCNC.

Auto Level

Now that the Probee is working, move on to auto leveling. The CAM tool, bCNC, has documentation describing how to perform auto leveling with with an electrical contact probe bCNC Auto Level.

Auto Level in bCNC with specific information for the Probee Probee, bCNC, and Auto Level.