Starting your own business in the same field

For a long time I’ve been thinking about starting my own company/brand. I’m wondering if anyone has experience starting a company that is the same field as your current “corporate” job? What is the etiquette on using factories and relationships that you currently use in your corporate job for manufacturing? Did you approach the manufacture and let them know you wanted to work on a personal project?

Those seems like some tough waters to navigate. I had friends who used manufacturing connections after they had left those jobs to start their own brands. Maybe they started in parallel, I don’t know, but it would seem rather risky if anything you did was considered competitive in any way.