how to start a mechanical engineering consulting firm.?
This is difficult. Usually you’d work as an engineer for a number of years and develop friends and contacts in the industry before forming your own business (so you’ll have customers). The other approach is to do contract engineering (small engineering jobs) and develop a reputation. Some regions of the country prefer not to hire outside consultants and would prefer to hire only employees, so consider the business culture of the region. If you wanted to start a ‘firm’ (multiple employees) you should already have secured a customer (it is comparitively easier to hire the additional engineers when you need them).