I use a cut off from half of an 18" fine-toothed hacksaw blade to get the nut slot down and cut at the correct angle and approximate height for the intonation to be as close as possible on the first 5 frets...
THEN I use whichever gauged welding tip cleaner matches the string diameter for the slot to simply and ONLY 'smooth' and ROUND the bottom of the slot.
I find that the welding tip cleaners cut too slow on anything other than cheap plastic, and due to being as flexible as a noodle, have too much waggle during the filing stroke to cut a perfectly parallel slot. Steel or not, with enough pressure to cut as a FILE, they sure bend an awful lot.
Also, if your hacksaw blade is hard to pull, lay it flat on the bench, on some stone or even wood block, and give it a couple of good passes of hard smacks with a hammer along the teeth, (perpendicular to the side of the blade)) up and down the length, both sides of the blade. This will flatten the teeth so they cut on the EDGE of the blade and NOT on the SIDES, which will leave a RAGGED side wall of your nut slots. Saw this tip in some luthery videos on YT a while back, but forgot who the person was.
Hope this helps....