The problem with making tools, is that eventually you have all the tools you really need. I have met this problem and figured out how to conquer it! Simply manufacture the need! In this case I have decided to make a mandolin.
This requires a bunch of new tools! Since I want to learn luthery, I have started out by doing repair, adjustment and fine tuning. Repairing a range of instruments means even more tools.
One such tool is for cutting or adjusting the notch in the nut to take a string. Ideally you want a perfect fit. Of course you could just buy a set of nut files, but since you need a nut file per string size this could mean four files for a basic mandolin. If you broaden you range, you can quickly find a need for quite a few nut files.
Here is a small collection of string sets;
Just to support one string set each for a modern mandolin, octave mandolin, bouzouki, antique mandolin and a bandurria requires quite a few unique string sizes. Even with some overlap, I still need 18 floats if I want to remain fairly precise.
Here is the vise I will use to make sure I have a precision gap. My scraper/scribe, dial calipers, and dollar store cleavers are also showing. I will need one cleaver per float, but at a dollar each the price is lower than the price of a nut file from any other source. I enjoy making tools, so the time spent is a wash. If I am making one float, it takes me about an hour unless I decide to put a new handle on it. 🙂 If I mass produce several at once, it takes me under 20 minutes per float.
The final result is not quite as fast as a fresh nut file, but it leaves a better finish, it is easy to clean out, it can be sharpened and best of all, this can have precision much better than a set of 12 nut files can provide. Additionally the wide blade makes it easier to sight down and make sure it is lined up to make straight cuts.
I am making this one the hard way, to illustrate the methods more clearly. Usually I would strip the handles of clamp them together with wet towels between them. I would wet them again and then Square the edge on a belt grinder, wetting regularly. Then I would wet them again and cut the notches with a cut off wheel all at the same time. By making the notches first, I reduce cleanup and finishing steps. After shaping and removing material to fix the profile, the notches are already cleaned up and pretty.
In the picture below the cleaver still has a curved edge. The curve needs to be ground away.
Here is a mandolin string being gripped by the vise with just enough force to give good resistance to pulling out the string, but not tight enough to deform the string or prevent the string from being removed.
As luck would have it, after squaring the edge, and cleaning up the taper, the blade fits perfectly. Sadly I am going to have to grind it down some just to show how the adjustment is done.
After grinding it, I use black magic to mark the blade. That’s right a black magic marker is a good way to make visible marks on a blade.
By putting the blade in the gap and using a scribe to mark, I can check to see if my grind is even and I can mark the material that needs to be removed.
I had to move the knife several times to mark the line. Since the line is straight my grinding job was straight as well. If you look below the knife you can see the granite slab with sandpaper on it. This is just one of the reasons the grinding job is straight.
In this picture you can see marks made to guide me in cutting notches. You can also see that I have ground down almost to the scribed line. After cutting the notches, I will grind to the line, round the edge and precision fit the blade to the gap in my vise.
Here are the preliminary notches made in the blade. They could be squared off a bit, but even rough they will do a great job. In the picture below the teeth look a bit uneven. For optimal performance the teeth are probably too even. I want an even enough gap so the teeth are strong and work out, but even teeth will not leave as fine a finish or cut as smoothly. This sounds a bit crazy, but the best rasps and floats are systematically random in their tooth placement.
By leaving a flat surface between the teeth, a much smoother stroke can be made. The tool is a bit less aggressive, but it is fast enough for my purposes. I sharpened the tip of this tool so that it can start with a clean straight line. Further back it will cut a more rounded notch.
As a comparison for speed of cut, if this were a file, I would consider it dull but not too dull to replace. The finish left is very clean. Another great advantage here is the ability to adjust the profile.