It's pretty much an established shop practice that bare tanged files should be handled, especially if used around rotating machinery like a lathe, mill, or a drill press. My old high school shop teacher delighted in telling us about the dangers of the unsheathed tang, and how it can be shoved into a wrist artery without warning and the hapless student would die a horrible death as he quickly bled out with no way to stop the bleeding- well, he was a little over the top but we all took his point that it would be a good idea to make sure to only use files with handles. A rocking chair my neighbor kicked to the curb provided my inspiration to thus fit out some of mine after inspecting the graceful curves it possessed, and so to home with me it went.
Step 1: Safety First
Objects may be heated to a high temperature in the course of this instruction, wear gloves when doing that step.
Step 2: Harvest Some Candidates
Decorative turnings on furniture can be a good source of ready to use prefinished hardwood stock for this project. After knocking apart the joints, grab up a likely looking piece and let your hand discover a comfortable section that may serve the purpose. Surprisingly, a fully round ball end wasn't the most comfortable feel but a truncated one was, and of even more importance was how the coves and slopes of the turning felt to the fingers as it was grasped, and that is what I focused on.
Step 3: Stepping the Tang Hole
After smoothing the cutoff ends, I used a center gauge to find the nominal middle and center punched it to prevent drill bit walking. I began to core the work with a smaller bit, about an 1/8” [3.3mm] diameter to establish a straight starter hole. Larger drill diameters were selected based on the tang's taper and length so some practice on scrap would be advisable before committing to the actual piece, however don't despair if it comes out wrong or too large, we can fix that in a later step.
Step 4: Fitment
Smaller files can be coupled in with a twisting motion until seated, forming their own taper. Usually that is sufficient for thin flats and rounds about 8” [200mm] or less in length. Larger or heavier files may benefit from the next procedure.
Step 5: Grocery Bags to the Rescue
After doing the fitment step, large files will be sloppy in the hole simply because so much material was removed that nothing much remains to stabilize the tang, so a hack using plastic bags will save the day, even on screw-ups of smaller files. Simply take a bag and stuff as much as possible down the mortised hole. Using a screwdriver as a ram, compress the bag material into the hole until no more can fit in, make it as solid a plug as you can.
Step 6: Hot Melting the Tang
This step is not as intimidating as it appears, it is simply a matter of heating the tang itself and shoving it into the stuffed mortise, literally melting it's way in and forming a perfect fusion with the handle. Using a vise to initially hold the file, heat the tang only, not the body, to a less than red hot temperature. I use a very damp sponge during the heat to daub the body end of the tang to keep heat back down where it belongs. Initially plunging the handle until it stops, I then quickly remove the file from the vise and finish pressing it home using the floor as a stop- this requires you really lean on it, and also keep checking your work to ensure it is reasonably inline with the handle. When cooled, it is really quite rigid and immediately usable.
Step 7: The Finished Products
Comfortable to the hand, made of solid hardwood, fairly well attractive, free prefinished material, and minimal tools used to fabricate- now that's my idea of an easy and fun improvement.
Step 8: Parting Thoughts
I have an assortment of free standing portable file racks at different work stations with file types suited to a particular use. I am a firm believer in chalking them up to help prevent loading since I frequently work in aluminum, which can be a gummy metal, and I usually find the chalk during asset recovery sweeps- kids are a good source of this, oftentimes just leaving big chunks roadside after marking out hopscotch boxes. I also keep a bamboo skewer handy to dislodge impacted metal from the teeth as well, so all in all I rarely have to resort to a file card for maintenance.