Gantry square procedure with PlanetCNC

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Many machines use two lead/ball screws rods per machine axis. In most cases, the Y axis.
Rods can be driven with one motor or two. One motor usually drives both rods using a timing belt, which also helps with
synchronization.

But you can also drive each rod with its separate motor. At PlanetCNC we use the terms Master and Slave motor.
PlanetCNC TNG software takes care of master and slave motor synchronization internally.

Nevertheless, between the two motors, there might be some discrepancy in a sense of gantry squareness. This can be due motor failure, lost steps, mechanical problems etc..

Since CNC machines are meant to ease the pain of accuracy and repeatability of machining process, we as users always strive
for squareness of our CNC machine.

In order to achieve this with dual motor setup, PlanetCNC TNG sw offers Gantry Square feature.

What gantry square feature does,  it “decouples” the master and slave axis motors from their common axis (e.g. Y), and assigns them new axis letters U and V, for the purpose of gantry square procedure. This needs to be done so that system is able to detect limit switches of each motor, as also to separately control each motor in order to  align gantry.

 

1. Setting the motors of Master and Slave axis

Under File/Settings/Motors we set additional (slave) motor of desired axis. In our case, axis output 4 will be used.

 

2. Settings Limit switches

Configuration of limit switch inputs for master and slave motor. We need to set limit switch inputs under motor U and V.

Motor U will have the same input number as motor Y, while motor V will have input number 4.

 

 

3. Gantry square parameters

Here we set the parameters of gantry square procedure.


Speed: 

Speed value at which gantry square procedure will be performed.

 

Axis:

Machine axis that will be squared. In our case Y.

 

Direction: 

Direction of squaring axis motion. It should be the same direction as set for limit switches for U and V.

 

Move U:

Value of measured misalignment of master axis. This is the distance for which master motor will retract.

 

Move V:

Value of measured misalignment of master axis. This is the distance for which slave motor will retract.

 

4. Using the gantry square procedure

Gantry procedure will consist of two takes. First will have values for Move UV at zero. Second take will use measured distances from the first take and use them for Move UV values.

We start the procedure under : Machine/Measure/Gantry square

Machine will move in direction set under Direction. Once first limit switch is activated, corresponding motor will stop, second motor will continue to move its side of the gantry until the second limit switch will be activated.

First we will set the Move U and Move V values to 0. This will give us the actual situation of gantry alignment. So after first actual use of procedure, we can mill or engrave a square. Then we can measure squareness of this square. Using a caliper we can measure the distance that needs to be compensated in order to achieve squareness of X and Y axis. This value is then inserted under Move U or Move V.