There are a few things you can ask welders before you hire them to get an idea of their experience and ability levels:

• Are you licensed and certified?

• How long have you been in the welding business?

• Do you commonly do the type of welding I need?

• Do you offer any kind of warranty for your work?

• Do you charge by the hour or by the project?

• How long do you expect my welding project to take?

• What steps do you take to minimize errors in your work?

Cutting rectangular ductwork requires careful measurements and the right technique. Use a measuring tape and pencil to mark the cutting lines accurately. Tin snips are excellent for straight cuts on smaller ducts. For more extensive or thicker rectangular ducts, a reciprocating saw with a metal-cutting blade is effective. 

Ensure the duct is well-supported and secure while cutting to prevent wobbling and maintain precision. After cutting, use a metal file to smooth any sharp edges, ensuring safety during installation. 

Professional metal fabricators typically charge around $70 per hour, but the total cost of your project will depend on several factors. The largest cost drivers are the size, complexity, and design of the project, as well as the price and type of metal used. A good way to estimate the total cost is to multiply the cost of raw materials by four; typically, one-quarter of the total goes toward materials and three-quarters toward labor. Your geographic location can also influence costs, as labor and material prices vary by region.

The best thing to cut metal pipe is a durable pipe cutter that is made for metal. You may want to measure the diameter of the pipes before purchasing a pipe cutter to ensure it will be able to cut your metal pipes. Opt for a heavy-duty option to cut through metal like steel or cast iron.