How to set motor & soft limits in PlanetCNC TNG software

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This tutorial will explain how to set motor and soft limits of your machine.

Soft limits (sometimes also program limits term is used) will stop machine motion when motor limit values of specific machine axis are achieved (without any limit switch activation). Soft limits will stop machine in soft stop fashion, meaning axis motors will use deceleration  – hence the name, soft limits.

 

First you need to configure step per unit values and limit switch inputs of controller:

How to set Steps Per Unit values in PlanetCNC TNG software

How to configure limit switch inputs of controller in PlanetCNC TNG software

 

Configuring motor and soft limits

You can configure motor limit values for each axis.

Limit- value sets limitation of axis movement in negative direction

Limit+ value sets limitation of axis movement in positive direction

Step 1:

First we need to set all machine and tool offsets values to zero.

Work offset should be set to zero with command “Machine/Work Position/Offset->To Zero”.

Tool offset should be set to zero with with command “Machine/Tool Offset -> To Zero”.

 

Step 2:

Now we need to choose where machine zero position is. Usually machine works in work position coordinates and it is not really important where machine zero is. What is important is that it is always at same position. I will put some tape to mark it so that you will see it better on image:

 

Tool is put in spindle and machine is jogged to this position. Use tool with normal length, not too short, not too long. Be careful not to crush tool into machine table when you descent Z axis. You can just loosely tighten tool in spindle and if accident happens nothing will be damaged.

This position should be machine zero. Command for zeroing machine position is in menu: “Machine/Machine Position ->To Zero”.

After using “To Zero” feature you will notice that values under Machine and Motors tab in coordinate position display will be zero for all axes:

 

Step 3:

Slowly jog Z axis up until Z+ limit switch is hit and machine stops. Step jog in opposite direction so that limit switch is released and write down Z+ axis machine position.

Slowly jog X axis in positive direction until X+ limit switch is hit and machine stops.  Step jog in opposite direction so that limit switch is released and write down X+ axis machine position.

Slowly jog X axis in negative direction until X- limit switch is hit and machine stops. Step jog in opposite direction so that limit switch is released and write down X- axis machine position.

Slowly jog Y axis in positive direction until Y+ limit switch is hit and machine stops.  Step jog in opposite direction so that limit switch is released and write down Y+ axis machine position.

Slowly jog Y axis in negative direction until Y- limit switch is hit and machine stops.  Step jog in opposite direction so that limit switch is released and write down Y- axis machine position.

PLEASE NOTE: Motor limit values obtained above are just an example on how you can obtain and define them. Motor limit values can be any values that suits your machine and application.

 

 

Step 4:

Now insert values that you previously written down(X+, X- ; Y+,Y-; Z+)  into Limit windows. If we want motors to stop when limits are reached, we must enable the radio button for desired axis. By doing this, we now set soft limits:

Step 5: Enable/Disable of soft limits

To enable soft limit settings, you need to make sure that they are enabled under: Machine/Motors,Limits,Probe/Soft Limits Enable

To observe Soft Limits enable/disable state, you can do that by observing:

-Machine/Motors,Limits,Probe/Soft Limits Enable menu. Checked for enabled, unchecked for disabled

-SL light under IO tab which will toggle according to above settings. Green when soft limits are enabled, and red when they are disabled