Leaving work as an employer to become a boss. Should I let know my old boss?

Hi, I'm 24, I've worked as an employee for 3 years now, as a graphic designer but even as a CNC, laser operator. This was my first working experience (as an employee) but I was already a graphic design freelancer. I like my job, we are a small company (4 employee), but I never felt like I was making enough, less than an average job and the boss knows it. I asked for a raise a year ago (it was an embarassing salary) but is still less than average. Now the question, since I saw some opportunity on my area with CNC, laser, printing and graphic design, should I let know my boss that I will soon become an competitor? Or do you think quit and start without even mentioning is a good idea? In my contract there was no competition clause, so that's not a problem. Thanks you 🙂