Welcome to the club of dead Dremel's Danny. I am on my third in fifty years. Not counting a Ryobi, no longer available, and a plethora of Dumore's.
Half round files, 6 and 8 inch have the best radius profiles. A dull file can cut ferrous metal, only a new sharp file can efficiently cut nonferrous metals. Be it Aluminum, brass. bronze, or copper. I have dozens of cast off files from a investment casting Co. whose aluminum wax casting molds I serviced and repaired.
MCS
MSC Industrial Supply - Metalworking tools and MRO Supplies (mscdirect.com)
Or
McMaster-Carr my personal favorite supplier.
Sculpting a radius with a file. It is a natural inclination to push the file from low to high. The opposite form from high to low gives the best control of the file strokes. ( From my Master Ray Nystrom, wounded at the Battle of the Bulge)
There after. Nick named Nine Finger Nystrom. In the heat of a Fire Fight Ray took a $hit, balanced with the aid of his M1. His middle finger of his right hand was shot off. One of the Nurses who cared for him became his wife.
Ray had a disadvantage, not being able to give a proper middle finger.
Memories.
A generous application of gorilla tape to isolate the adjacent tubing, while whittling away and fairing the brass joints may be useful. Mind you, everything I have said about metal working is not recommended, except the file remarks.
Tom