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The axis reached the end of its permitted travel or tried to go past it. The machine stops and blocks motion in that direction, but it lets you move back the other way. In the vast majority of cases there is no fault: the work offset, an offset value or the program start point is wrong, and the control just saved you from a crash.
For reference only: alarms change with the manufacturer, the control and the machine PLC. Check the full code in the official manual before doing anything. Legal notice.
If the axis does not release, the limit switch remains active or there is a mechanical shock.
Exit the limit manually following the OEM procedure and then reset.
The overtravel release method depends on the machine manufacturer.
Choose the manual matching your control series, software version and machine builder. A support portal is a starting point; it does not establish applicability to every model.
An axis has two levels of travel protection. The first is software: the control stores maximum and minimum limits for each axis in machine coordinates, and before executing a move it compares the destination against them; if it falls outside, the move never starts, or it is stopped on reaching the limit. The second is hardware: a physical limit switch near the real end of travel, which acts even if the control is lost. Software protection is only trustworthy if the axis has been referenced, because the limits are held in machine coordinates and without reference return the control does not really know where it is. When OT0500 trips, what happened is that the commanded position, once the work offset, the tool offsets and the program geometry are added up, fell outside the permitted window. That is why the error is almost never in the axis: it is in the sum. A G54 measured with the wrong tool, one length offset too many, a part clamped two hundred millimetres higher than last time, or a program started from a block in the middle where the control had not yet read the correct coordinate system will all shift the whole job outside the machine's usable envelope.
In order, from the fastest and cheapest check to the most expensive.
01Identify the axis and direction, and move back the safe way
The alarm tells you the axis and whether it was positive or negative. Jog slowly, only in the opposite direction to the limit. If you try to move in the blocked direction it will not let you, and that is exactly right. Getting the axis out does not fix the cause, it only frees the machine.
02Check that the machine has been referenced
If it has just been switched on and no reference return was done, the software limits do not apply and the axis will run into the physical stop. Confirm it by looking for the reference marks on the position display. If they are missing, do the reference return using the normal procedure before anything else.
03Check the active work coordinate system and its value
Look at which G54, G55 or whichever is active right then and what values it holds. A work offset with an extra digit in Z or with the sign flipped sends the tool straight into the limit switch. Compare against the value it had the last time the job ran correctly; if it is written on the setup sheet, it takes a minute.
04Check the length offset of the tool that is loaded
An offset measured too long, an H called that does not match the T in the spindle, or wear entered with the wrong sign will all make Z demand travel the machine does not have. Verify that the offset number matches the actual tool and that the length makes sense compared with the physical tool.
05Find the block that commanded the move
See which line the program stopped on and what coordinate it was asking for. If it is a retract to a tool change or a safety positioning move, it is usually the work offset or a tool offset. If it is a coordinate from the part geometry itself, check that the workholding and the part position are what was assumed when it was programmed. If the program was started from the middle, start again from the top.
06If the axis will not release or a hard limit switch is tripped
That is no longer an operator task. Every builder has its own procedure for backing an axis off a hard limit and it varies a great deal from machine to machine. Call maintenance with the machine manual in hand. A limit switch is never defeated or bypassed just to be able to move.
Work offset or tool offset is wrong. Confirm it by comparing the G54 and the offset against the values on the setup sheet, or by measuring again. The program itself is usually fine.
The job no longer fits in the usable travel with that setup. Confirm it by adding up part height plus vice plus the longest tool by hand and comparing against the machine's Z stroke. The answer is to change the setup, shorten tools or move the job to another machine, never to force the limits.
The control never read the correct coordinate system or length compensation, so the first move goes to nonsense coordinates. It is confirmed by the fact that it never happens from the top of the program. The only safe way to restart is from a start block that restates the whole modal state.
Work offsets and tool offsets written on each job's setup sheet, with a quick cross-check before the first part of the batch. Always run the first part with rapid override reduced and a hand near the feed hold, which is the habit that prevents half the scares. Standardised setups, with known vice heights and stops, so the Z travel arithmetic is always the same. Safe restart blocks spread through the program so you can resume without improvising. And check the travel in CAM simulation using the real setup height, not the theoretical one.
An axis has reached or attempted to exceed the allowed stroke limit. It is an alarm from the Sobrecarrera area, and in the catalog it is listed as “Axis overtravel”. On the machine you notice it like this: The axis stops near a limit switch, It does not allow movement in the direction of the alarm.
On the shop floor it almost always comes from one of these causes: Zero wrong piece, Program started from an unsecured line, Offset or incorrectly measured tool, Software/hardware limit reached. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Exit the limit manually following the OEM procedure and then reset. Resetting without fixing the cause first only hides the problem: OT0500 trips again and, in the meantime, you keep working with the machine in bad shape.
With the machine stopped and in a safe state, start with these checks: Check G54/G55 and offsets, Move only in exit direction with safe manual mode, Review line that commanded the movement. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With OT0500 active, avoid this: Do not release limit switches without knowing which axis is involved, Do not continue with the program without correcting origin/offset. Skipping any of these points is what turns a minor stop into an expensive breakdown.
If the axis does not release, the limit switch remains active or there is a mechanical shock. If you are not sure how far it goes, stop the machine and report it: a repeat alarm always works out cheaper than a crash.
It is a stop alarm: the cycle will not continue until you fix the cause. It does not always mean serious damage, but it leaves the machine where it is and you have to check it before running again. The overtravel release method depends on the machine manufacturer.
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