I am constantly looking for ways to improve my accuracy and I have settled on a new method for spacing strings when cutting a new nut.
The goal when making a new nut is to get equal spacing between each string. Since the strings have different diameters the spacing between them is unequal. Special rulers are available that compensate for the unequal spacing, which do a good job, but hand marking and filing the slots can introduce errors which are very noticeable in the finished nut.
The nut on the ’72 Stratocaster illustrates how small spacing differences are easily visible. I recently refretted this guitar leaving the nut slots too low for the new frets and need to replace it.
To ensure the correct spacing I use a small Sherline vertical milling machine and a dial indicator. The milling machine is fitted with a circular saw blade .020″ thick. Other thicknesses are available but this gives a good size groove to later guide the nut slotting files for the proper width of each string. The dial indicator is graduated in .001″ increments and accurately measures the movement of the milling machine table.
Using digital caliper I measure the distance between the outside strings and a simple spreadsheet is used to calculate the spacing between each string taking the different string diameters into account. Once the calculations are complete it is a simple matter of cutting the first slot, zeroing the dial indicator, and moving the table the proper distance to the next string slot. Repeating the process for the 5 spaces on a 6 string guitar completes the layout. The slots are filed to the proper width for each string and the nut can be fitted and shaped as usual.
This method has proved to be both accurate and efficient and the spreadsheet can be modified to account for different types of instruments.