Razor saw

[MIGNAL]

I have a few. The one I recommend is a Grobet/Vallorbe cut 2 @ 140 mm's. That's the one with a very fine point, or at least mine is. I also have one at 160 mm's but the tip is a bit wider.
All were bought from Axminster, years ago. I don't think they stock them now. They do have the Bahco but I've no experience of those. Try jewellery/watch repair sites.
These very fine tips are easily broken. You have to be extremely gentle and allow the file to cut rather than have any weight in the hand. I broke a couple before it finally hit home. My current one has been OK for 6 or 7 years. For the wider strings you can be a lot more heavy handed. The 'secret' is to get the height of the Nut finalised (or very near). That way you are virtually just scratching a groove (for the very thin strings). Theory states that it should sit at half string - 0.15 mm's for a 0.3 mm string. That's not exactly a very deep groove! The strings should look like they are sitting on top of the Nut rather than sitting in it. Practice on dummy wood top nuts. Actually Ebony makes for a decent bone substitute for Nylon strings and will probably last a few months on steel.
BTW if you do break the tip you can grind down two opposite edges - creating your own tapered 'joint round edge' file. That works as well.

 

[Kalimna]

Thanks for that, I shall search out some files.
Cheers
Adam

 

[dh7892]

So you cut a v slightly high and run it in?
What happens if you change string gauge?

If you prefer a very low string action, you would completely set up the guitar again if switching to a different gauge. (intonation, truss-rod, saddle-height). If you like a higher action, you could get away with it.

When I make my next guitar, I think I'll go with the zero-fret option. I think it has a lot of benefits and actually make the construction easier as far as I can see. Then the nut just becomes a string guide and you can afford a bit more margin for error.

 

[whiskywill]

As already mentioned, some use welding nozzle cleaners like these. http://www.ebay.co.uk/itm/Gas-Welding-T ... 885wt_1207
I find they work OK.

 

[Edwin]

If a string was, say, 0.3mm in diameter and a semicircular groove of 1mm diameter was cut so that the lowest part of the groove was in the correct string position, wouldn't the string just sit at the bottom of it without having to be supported halfway around its circumference?

 

[thick_mike]

If a string was, say, 0.3mm in diameter and a semicircular groove of 1mm diameter was cut so that the lowest part of the groove was in the correct string position, wouldn't the string just sit at the bottom of it without having to be supported halfway around its circumference?

I don't think the match of groove to string has to be perfect, but if the slots are too large the string moves about (e.g. when bending notes). This can cause buzzing.

This page from Frets.com explains a bit about nut slots...

http://www.frets.com/FretsPages/Musician/GenSetup/Nuts/nuts3.html

By the way, frets.com is a great resource. Loads of info about guitar set up, repair, history as well as a treasure trove of shop tips that apply to general woodworking as much as lutherie.