Thats great Stuart, you will have that steel singing and playing great soon.
Low strings in the nut are no fun and one of my pet peeves. To compensate, you end up mashing down the bar which not only is uncomfortable, but throws the tuning balance amongst all the strings as a whole out of whack.
Like many things in life, there are many ways to get there. Triangle files and tip cleaners can get the job done, but there are compromises. Idealy, you want a string slot just a little larger than the string diameter with a round bottom. A triangle file makes a V shaped slot and while tip cleaners are round, they are not made for serious material removal and the small sizes are pretty flimsy. In a pinch, you could certainly use a triangle file to get you most of the way there and followed up with a tip cleaner to round out the bottom. A tedious adventure no doubt.
Another DIY method is to make some little saws / files out of feeler gauges. Take a file and round off the edges, then cut / file some teeth on the edge. Don't expect to be removing a lot of material with them, but they can work a little better than the flexing tip cleaners.
Its hard to justify spending $100 or more for a set of files that you only plan to use once. Years back when I made my very first steel, I explored all kinds of different options. It it did not take me long to pony up and get a proper set. In the end, there is nothing like having the proper tool for the job.
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