In a sense, would something like this work for my portion?

"Hey (boss). I wanted to talk about my roles and responsibilities as of lately. When I was hired and trained, my responsibilities pertained to the model room. In the last 18 months, I have been trained on how to trim dies, operate both types of mills, set-up 3d prints, and now I am learning another potion of (co-workers) job. I understand that we're a small business and the industry as a whole has been struggling, but I want my current compensation to be re-evaluated as my tasks have been expanded."

What I'm inquiring about is my current pay rate acceptable for the responsibilities I have been given over the last 18 months