Here's a little handle to turn your bare-ended needle file set into proper tools.
Much easier to work with.

Print with a raft so it stays stable while printing.
The size of those file shafts varies a bit so I've made the handle holes 3mm and drilled out to 3.2mm for a good fit, adding a drop of foaming gorilla glue to keep them in. Alternatively, scale the STL as required.

I printed at 15% fill and 2 shells, and if your setup is anything like mine you'll have a neat little musical groove going while it's printing.