Program exceeds machine min on Z

[Masons Forge]

Hey Guys
I changed to the Linux system 2yrs ago and it has worked fine until this week. It was cutting fine then it moved to the next cut and would not touch off, I tried the Run From and still nothing. I loaded another file and it would make the first cut move to the next and do nothing. Now I load a file that I have cut many times and I get the message "Program exceeds machine min on Z limit" If I raise the torch up over two inches and Zero it out then I don't get the message but it wont move down enough to touch off. I even changed the limits to 2in and then I get the message again. I'm using a SuperZ II with ohmic and safety switch to touch off. I haven't changes any settings. Does anyone have any suggestions?
Thanks Josh

[acourtjester]

I had the same problem a short time ago with the Axis GUI. What I changed was the length of the Z travel in the INI file, you could change it in the Pncconf setup too. In the INI file there are 2 lines you need to change or you get an error when starting the GUI. I increase mine about 3" from -4.5 to 7 did not have the problem after that. If you are not using QTPlasmaC for plasma you may look into it, very nice great options have been added.

Z non zero 3.JPG

[tcaudle]

That comes from using SOFT LIMITS (settings in each axis in the configuration tool that set MIN and MAX travel . Soft limits REQUIRE that you have HOMES on each axis and that you Home the table each time you fire it up. What i does is try to keep you from exceeding the limits of the tab;le and that message is telling you that a move in the software will cause it to runoff the rails.

Now, if you do not use HOMEs and the Min and Max are set at some high number in theory they should not trigger that STOP. But what can happen is of long times and not doing a HOME move and zeroing the axis using the buttons you build up a huge OFFSET and finally a normal move then triggers that ERROR.

Solution: one Add Home switches to the XY and Z axis and use them and ZERO the readouts when each one homes .
Set the Min and max travel to reasonable numbers in negative and positive ends (don't set the min at 0.00 because you will have moves that possibly go to 0.00) make it a negative number

Solution two No home switches : Set the XY and Z homes in the INPUTS to "not used" Make it a habit to manually jog each axis to its table Zero spot (Home) and simply hit the Home button. It will home it where it is and then zero the DRO.
That will remove any offsets (which are what are causing your errors.

You can see axis offsets if you open the CURRENT OFFSETS mien in the right hand side bar (upper right of screen)

All the software is trying to tell you is it thinks you are going to run off the end of the table with one of the moves in the code because its built up a ton of offsets.

So my advice is to install Homes if don't have them and use them daily . It offers you a way to get back to the same exact starting point no matter where you decided to set WORK Zero (reading on the DRO's)

Linuxcnc relates everything to the TABLE ZEROS (HOMES). Everything else is an Offset for that

Turn off SOFT LIMITS. Sett he axis travel limits in the AXIS tabs for each axis to a large negative number of MIN and a large + number for max on each axis.

[tcaudle]

BTW because Z Home is the top of material it changes . Do not try to set a number in the Z axis Min and Max travel that is close to normal numbers. Touch off preforms what you need for Z position and soft limits are not going to help. Set them to -9999 min and 9999 max. In short do not use Z homes for soft limits

Selection_217.png

This screen is using Homes and using Axis travel Limits (soft limits) On of the uses for homes is to be able to actually establish the table zero (home) at some spot beside where the switch is. In this case The switch is mounted a the back of the tble in Y and we need the table zero to be front left so its offset 48 inches and then it moves to 44 after it homes and zeros

[acourtjester]

I am not the expert you are Tom but I do disagree with your statement "BTW because Z Home is the top of material it changes" my Z home is a the top of Z travel. I want my torch or router bit far away from the material or slats when I home X and Y axis actions. Unless you are talking about setting Z 0.0 at the start of an operation as a home position.

Z non zero 3.JPG

[tcaudle]

Homes are best described as like you address where you live......A known location . In the Linuxcnc ( and a lot of commercial controls) it's table zero points . Everything is measured in reference to those table zero points. The Work zero set by the DRO readout and the ZERO buttons, is just relative point like if you work out of a mobile base away from you house. In the system the internal location is kept as an OFFSET from the Homes . Even though the readout may say X = 1.000, internally its kept as the true distance from the X home offset which can be any place on the table.

Z home is not a true fixed home when you deal with plasma because the work moves on you . A fixed Z home at the top of the Z wokrs great for routing and milling since it can be a fixed distance above the Z top of Cut surface and you can do g-code that uses that as the the Z reference and the cut is a precise amount above that. In plasma you are not cutting into the materiel and the material moves (warps) on you. The only reference you have is to find the top of materiel and sett the Pierce height and cut height from that . My statement that "Z home moves" is not really correct . It would be better to say its not a useful parameter in plasma cutting. There is no G-code in Linuxcnc to call a HOME Move.

The error the user was getting simply says it thinks that a move in the code would cause the table to ruin past its max on min travel distance. Since that point is based on the HOME zero, if its not physically set, it can become confused regardless of where the DRO says the axis is .

Several things are measured in Home Zeros (Absolute zero ) Our LOAD MATERIAL is in absolute units and if you use our Tool Setter and toolchange POSTS for router/spindle those locations are Absolute (never move around)

Sometimes you have to know where you are on the table in absolute terms.

[Masons Forge]

I rehomed the Z and it is working. I would like to add XYZ home switches, but I hate to open the box because it is cutting and I'm not a production shop. I'll probably add them over the summer when school is out.
Thank you

[acourtjester]

If you are adding limit/home switches I would recommend you use proximity sensors not switches. they work great and are water and dust proof and use between 6 to 36 volts supply. this is the ones I used and you can use one per axis. I used a 10-32 machine screw as the trip point shown in the video. But you will need one input for each axis. I bought them from Amazon for $12 for 3. Comimark 3Pcs TL-W5MC1 5mm 3 Wire Inductive Proximity Sensor Detection Switch NPN DC 6-36V
video showing how they work.

[SegoMan DeSigns]

I agree with Tom on this one, these are the ones I used:

https://www.ebay.com/itm/301801247259?_ ... BMjMXo89tk

Chain Drive, Finale Drive.jpg

PNP W Bump Stop.jpg

I originally used mechanical (with a custom over-run spring bracket) but they did not survive the occasional IDTenT (ID10T) error codes I threw:

Limits, Old Style.jpg

[tcaudle]

I rehomed the Z and it is working. I would like to add XYZ home switches, but I hate to open the box because it is cutting and I'm not a production shop. I'll probably add them over the summer when school is out.
Thank you

Good!

It must be an older model because the G5 series has the lter Table I/O 17 (with 16 inputs and the 12 pin cable connection for the FT-02) mounted on the outside where it easy to connect any type of sensor/switch and it has an option to power external sensor with the INPUT 12V source.

The 12.6 Table I/O was still inside but it does have added inputs and a way to connect the FT-02 Ohmic sensor. The FT-02 also has 4 inputs on the module (up on the gantry where its easy to mount and connect all three axis of Homes )

Homes are nice to have and much more functional than limits (although you can make a switch do BOTH)
Having a known zero place on your table lets you never lose where you are (work zero ) no matter what you do . The offsets are stored in a variable and only go away if you re-zero the WORK (DRO's) As long as you don't move the material then you can get back and re-cut or continue at any time.

When we did production we had locator tabs on the table that let us load a sheet square in X and Y so everything had the same work zero . Short of that a crosshair laser can get you real close even if the material gets moved.

I have found that proximity sensors are great for general detection but they can have less than perfect repeatability in varying conditions . Having a small target can help but their sense distance can vary some over time and even change with plasma dust . They work a LOT better on ferrous metal than AL or stainless. Their sensing distance can be double with steel versus Aluminum. Still its better than no sensors! On Homes having them trigger at the exact same spot every time regardless of the homing speed or the environmental conditions is important if you ever wan to re-home and pickup an interrupted cut .

The Inputs on the controllers are isolated to reject noise (do not share the same ground as motors /and the control) As a result if you use powered sensors you have to supply a separate "floating" power source that shares the same ground (common) as the inputs . Just tie the external supply ground terminal to the COMMON input of the Table I/O card (there are several) . You can use any voltage from 5 to 24 DC if you supply the power.


Every time you fire the puppy up its a good idea to at least move each axis over to what you would call a "home" and hit the HOME button . It sets that as the new HOME. Won't help keeping positions but it will keep you from getting that "out of Range" error.

[novavoyager]

Thanks for the information.