Homing is one of the most important parts of CNC operation. Without homing, MASSO doesn't know where the axes are after power-up, which can prevent proper operation and may cause machine crashes. This page explains the homing methods available and how to set up homing on your machine.

Once homing is complete, the homing sensor also acts as the hard limit sensor: the same sensor establishes machine home and detects when the machine tries to move beyond its allowed travel.

To start a homing cycle on a machine that is already set up, see Homing the machine.

1. Homing methods

Auto Homing

Auto Homing is the recommended method. Each axis to be homed needs its own homing sensor – on a three-axis mill, sensors on X, Y and Z.

If an axis is hardware-slaved (two motors driven from the same axis output), only one homing sensor is needed for that axis, because both motors move together.

Auto Homing with axis squaring

This applies when software slaving is used. Each motor on the dual-drive axis is connected to a separate axis output, such as Y and B, and each motor has its own homing sensor. During homing, each motor moves independently until its sensor triggers. The first motor to reach its sensor stops and waits for the second. Once both have found their sensors, they back off and lock together as a single axis.

The relative position of the two sensors determines the squareness of the axis. Squaring is best done by physically adjusting one sensor relative to the other. Pull-off distance can be used for small corrections, but it forces the axis out of square and back into square on every homing cycle, so use it only for minor adjustments.

Manual homing and stall homing

Manual homing means jogging the axes to a known, repeatable location and setting that position as home by double-clicking the Home button. Stall homing is a variation where the axes are jogged until they stall against physical stops, giving a repeatable position that is then set as home.

These methods don't need homing sensors. Untick all axes in the Homing Sequence; each axis is then assigned its Home Position value when homing completes.

2. Mounting the homing sensors

Mount a homing sensor or switch on each axis. Mounting it at the axis 0.00 position is simplest, but any location works – set the Home Position value to match where the sensor is mounted (see Home Position).

Traditionally, homing sensors and limit switches are mounted at the extreme ends of travel and wired individually back to the controller. That uses more wiring, hardware and controller inputs than necessary – homing sensors work very effectively with soft limits alone.

When a homing sensor is also used as a hard limit sensor, mount the sensor on the moving axis carriage with fixed triggers at each end of travel. A single sensor is then triggered at both ends. The trigger must keep the sensor High for the full homing process.

Sensor on the moving carriage, trigger on the stationary rail.

If a machine already has homing and limit sensors at each end of an axis, multiplex them onto the axis homing input so that triggering either sensor changes the input from Low to High. See Sensor Identify & Connecting for multiplexing, third-party sensor types and wiring, and MASSO Homing Sensor for the MASSO sensor.

3. Assigning homing inputs

The input status changes from L to H when the sensor triggers. Use this to check each sensor before homing.

4. The homing process

Start homing by double-clicking or double-tapping the Home indicator on screen, by pressing Ctrl + Alt + Home, or with an external Home Machine button. Whatever the method, the homing cycle has four phases:

5. Homing settings

Homing is configured in the Homing Settings window. Each setting is described below; for a quick field-by-field list, see Homing Settings.

Homing Sequence

Sets the order in which axes are homed. Axes in the same sequence home together, and sequences run in order from SEQ 1 to SEQ 5. For a typical mill or router:

• SEQ 1: Z axis only, to lift the tool clear of the workpiece first.
• SEQ 2: X and Y axes together.

Software-slaved axes are greyed out and can't be selected independently . A slaved axis may appear ticked or unticked from previous settings, but it is always controlled by its master axis and homes correctly either way .

Any axis not selected in the Homing Sequence is assigned its Home Position value at the end of homing.

Direction Invert

Sets the direction an axis moves while seeking its sensor. If an axis moves away from its sensor during homing, press Esc (Feed Hold) to stop the cycle, then invert the homing direction for that axis.

On a software-slaved axis, the homing direction of the master and slave axes can be set individually. The correct setting depends on the machine's mechanical and electrical design – check that each motor moves toward its own sensor before running a full homing cycle.

Homing Feedrate

Sets how fast the axis moves while searching for its sensor. The maximum usable feedrate is limited by axis acceleration: lower acceleration means a longer stopping distance after the sensor triggers. The axis must stop within 10 mm (0.394 in) of the trigger point or a homing alarm occurs. Axes with higher acceleration can use higher homing feedrates; axes with lower acceleration need slower homing speeds.

Back off

Back off precisely locates the point where the sensor returns to Low, which sets the primary home position. The trigger must keep the sensor High until the axis has fully stopped, and must be long enough to stay High for at least 10 mm (0.394 in) of axis movement.

If the sensor doesn't return to Low within 10 mm (0.394 in) during back off, a homing alarm is generated. If the sensor returns to Low during deceleration, back off doesn't occur. If the axis can't back off within 10 mm, reduce the homing feedrate so the axis stops in a shorter distance.

Pull-Off Distance

Moves the axis away from the sensor after back off. On MASSO G3 and MASSO G3 Touch it can be set individually for each axis.

• It creates a safe gap between the sensor and the axis when hard limits are enabled, reducing false hard-limit alarms.
• On software-slaved axes, both motors normally use the same pull-off distance. Small differences can be used for minor squaring corrections only.
• If homing sensors are outside the soft limits, for example in a tool-change area, use the pull-off distance to bring the axis back inside the soft limits before homing completes. Otherwise a homing or soft-limit alarm may occur.

Home Position

Sets the machine coordinate assigned to the final axis position at the end of homing. It defines the machine coordinate system and the G28 home position.

• If the sensor is mounted at 0.00, set Home Position to 0.00.
• If the sensor is mounted elsewhere, for example 400 mm (15.748 in) along the axis, set Home Position to that value.

Home Position doesn't have to be zero. For example, if the machine homes at the rear of the table but machine coordinates should start at the front, set Home Position to the full axis travel. On long Z axes, Home Position can place Z0 lower down the axis, which controls how high Z rises during tool changes, Auto Tool Zero, Jump to Line and plasma operations.

Request Home on Startup and after E-Stop

6. Videos

Setting up homing step by step

Homing setup with homing sensors

7. Troubleshooting

For homing alarms and other homing problems, see Homing troubleshooting.