It allows you to automatically set the Z height to your workpiece top surface or your machine’s bed surface.

To use it, you simply place the sensor on top of your work material or on top of your bed, and then move the gantry so the tip of the end mill is just about the button on the sensor.  Then you can press the Tool Length button on UCCNC and it will automatically lower the bit until it touches the sensor.  Once complete you remove the sensor and when you press “Go to zero” on UCCNC you will notice that the tip of the end mill is exactly on top of the workpiece’s surface.

Here is a video that explains how to set it up and use it:

If I order a STEPCRAFT CNC Ready To Run with a Tool Length Sensor, will the sensor be ready to use when I get the machine

When you order a Tool Length Sensor with your Ready To Run STEPCRAFT CNC, the tool length sensor will be wired and ready to use.  You will have to install the macro for the tool length sensor (see video below) into your computer to get it to work.  Depending on when you purchase your machine, the Tool Length Sensor will either be wired in directly to the machine, or there will be a headphone jack that you can plug it into coming out the back of the machine.