Soft Limits are your Friend

Soft limits can be a little confusing at times to those who are not used to them. They can be even more confusing when the program you have previously been using now gives a soft limit warning when previously it ran just fine and has done so many times before.

The first thing to understand is what a soft limit is.

Soft limits define the limits of your machine. They define how wide, deep and tall the working area is and MASSO uses this information to determine if the program will stray outside of these constraints when a program is run.

Soft limits are there to prevent the machine crashing at its extremes of travel or into your tool changer if you have one.

To understand soft limits you first need to know that there are 2 different but interconnected coordinate systems used on a CNC machine. The first is Machine coordinates and the 2nd is working coordinates.

You can see both coordinate systems on the F2 screen of your MASSO

The larger DRO (Digital Readout) values for X,Y,Z A & B axis are the working coordinates while the Smaller ones in the bottom right under the MACHINE banner are the machine coordinates.

The Soft Limit alarm
If you see a soft limit alarm you can use the information on the alarm MASSO to establish where the problem is. In this example a program that has run without a problem has this time given a Soft Limit alarm on line 41 and it tells us that the problem is related to the Z axis

It is requesting a move to working coordinate Z-10mm

Finding the problem
Finding the problem can be as simple as jogging the machine. You can sit down and calculate offsets, maximum and minimum travel but the easiest way is to jog the machine and read the screen. Since we know the problem is the Z axis we just need to move the spindle to a clear area on the table and jog the Z axis down as far as it will go towards Z-10 and see the travel allowed.

After jogging down as far as The Z axis will allow, we can see that the Z axis has Machine Coordinate -75 which is the maximum allowed in the axis settings but it is only reached Working Coordinate Z-9.5mm. It cannot go lower to the requested Z-10 and this is why we get the soft limit alarm for this line of code.
It should be noted that a violation of a soft limit only needs to exceed the limit no matter how large or how small the violation is. To the machine 100mm is as bad as 0.00001mm

If you need assistance for others to help you find the problem you need to share a screen print of the F2 screen showing the Softlimit alarm. A copy of your printable file and the Gcode file that caused the soft limit. These 3 items contain all the information to find the cause of the soft limit problem.

Solutions
So why did this machine work correctly in the past but failed this time?
The most likely answer is that the tool you are using is shorter than the one used previously so cannot reach as far down. If it is the same tool that was used last time then it will be because the tool is inserted further into the collet than on previous occasions so had more reach.
After sorting the tool, you can rehome the machine to get a new measurement on the Auto Tool zero and then re zero your tool to the material. After that a jump to line will allow you to resume your machining.

The similar situation may arise when the Z axis rises to the top of the axis. If the tool is too long it may hit the soft limit at the top of the Z axis. It could be as simple as the tool sticking a little too far out of the collet and sliding it a little further into the collet may be all that is required to prevent the alarm.

Material placement on the table will determine X & Y axis soft limit alarms. Projects that approach the maximum table size need to be carefully placed to ensure you do not stray outside of your machine’s soft limits.

Tool Changers
Tool changers such as a linear tool changer which resides on a portion of the table can be placed outside of the soft limit area. This has the advantage that the tool changer is protected from crashes while machining and when jogging as moving into this area is prohibited unless performing a tool change.

Disabling Soft Limits
There is an option in the Machine settings to disable soft limits.
Disabling the Soft limits only applies while machining and does not apply to jogging the machine. While jogging soft limits will prevent the spindle or other head from straying outside the soft limit area which will continue to protect the machine from accidental damage such as jogging into the end of the axis or into the tool changer.

Disabling soft limits will prevent alarms from occurring while machining. It will not stop the machine when it exceeds a soft limit value while running a Gcode program. This may lead to the machine crashing into the end of its travel or it may crash into a tool changer or other protected areas.

Soft Limits are your friend and can prevent damage to your machine or work. It is better to stop what you are doing and find the problem and fix it than to disable the soft limits and run without them. Sure, there may be enough travel in the axis to overcome that 0.5mm of over travel you had and you may get away with it. But remember this was just one line of Gcode in a program that is many lines long and somewhere in the program there may be a move even deeper that will crash the machine and ruin your work.

Remember that soft limits are there to help before there is a problem. I hope this provides some insight as to what they are and how they can help you as well as how to deal with them then you see one.