Hi Folks,
My name is Rab and I'm desperate for help. I retired last year and decided to take up CNC as a hobby to keep me occupied. I bought a second-hand machine which is in very good condition, it has a cutting area of approx. 900mmX360mm. I'm using Carvco Maker along with Mach3. My problem is when I take a simple design say a circle or square and try to run it, regardless of what I try, the router tries to go off the back of the machine and the right-hand side. It works fine when I use the Mach3 tests such as roadrunner but for anything else, it just goes beyond the limits. I haven't bought the Mach3 license yet until I know it's working and have my table limits set to 700mmX350mm and suspect it has something to do with the settings. Having said all that, I'm a total novice and everything I've learned, which isn't much, I've got from youtube.
Any help you can offer me would be greatly appreciated.

Not sure you have this manual:

https://www.machsupport.com/wp-content/uploads/2013/02/Mach3Mill_1.84.pdf

in chapter 7 are some explanations about coordinate system and offsets.
this might help.

anyhow, if machine tryes to go behind limits it has normaly to do with coordinate system or origin or even
the units (mm/inch) you are using.

Hello Rab, welcome to the forum.  I guess you maybe like me of an age where printed explanations are more useful than videos so I second TPS' suggestion to get a copy of the manual.  It could be useful to carefully save the xml backup file of your machine (read the manual) and then go right through the Mach3 setup process to make sure all the settings are correct, and you will learn a lot in the process. If an existing gcode file like roadrunner works though that should indicate that the setup is OK.  Could you post some gcode from Carvco that doesn't work?  BTW, it is worth buying a licence even though the cost for a piece of software that isn't supported except through a user forum is a bit steep.