I need to cut nice clean squares in the side of some 18 guage steel tube. Can I use an angle grinder with a?
thin metal cutting disk? i have tried other tools such as metal cutting circular saws but this is too difficult to get a straight line from.
Answers below in Comments Section

You can try using the grinder, but that really sounds like a job for a mill. I think you’ll be setting yourself up for some serious hand filing if you use the grinder with a cutoff wheel.