Whilst playing "vigorously" two things happened to my bass. The E string broke and the end of the nut chipped off. I still don't know which caused which, bit that didn't matter when I was playing within 24 hours of being able to get to a shop.
Instead of buying a new nut, which seemed boring, and isn't really my way of doing things, I decided to fabricate one. Given that I was changing the strings anyway, it seemed like the right time to try my re-stringing plan. I rarely use the G-string in actual playing, as guitarists exist for those notes, and I like my bass bassey. However, I want the notes just slightly below E regularly. Unable to afford a five string, and not having a workshop to build one in, it seemed the next best thing was to use the D, A, E and B strings from a five string set, essentially moving my bass' range down by a fifth.
After searching work for some suitable material for the new one I found a small heatsink, with a flat base as wide as the old nut. I measured the old nut, made adjustments for my new tuning (basically just wider slots) and then set to work.
I drilled the holes for the strings, which would eventually become slots, but didn't have a wide enough range of drills to get them all perfect. This doesn't seem to affect the sound though, so I'm not too bothered.
I'd planned to angle grind the main forms, but the weather meant outside wasn't ideal (or safe), and inside was forbidden, so my crappy little junior hacksaw had to do. An hour or two later and it was all cut to shape. A bit of emery and I had it looking all-right too.
Then came the trickiest bit - removing the old nut. I began by hacksawing down the middle, which did very little to help, and then chipped the rest away, carefully, with a chisel. At one point I wasn't quite careful enough, and chipped off a small piece of neck (thankfully on the head side). Araldite fixed this, but I was hoping to wouldn't happen.
If trying this, wear eye protection - I'm not a fan off PPE for every activity ever, but when a chip jumps into your eye it hurts, and wastes 15 minutes whilst you try to sort it. In my case it got lost, and resurfaced later when I was shaving, which was at least slightly unnerving!
Once the old nut was removed I could sand and file the new one to fit. I also adjusted the slot slightly, though only on the head side, as the neck side plays quite an important part in the pitch of (open) notes.
Once the fit was snug I mixed some Araldite up and glued it in place. I then tuned it, tuned it again, tuned it a third time, and eventually realised the tension in the strings was tilting the new nut over - it seemed I'd been a little hasty in tuning. A quick application of a g-clamp straightened it out, and after a couple of hours it was set enough to play.
That gave me a whole hour of practising on my new tuning before I played at Church the next morning!