I used a homemade template... get the measurement from
http://www.floydrose.com/instructions.html and trace the lines onto a piece of 1/2" (or thicker) plywood. Cut the hole out with a jig saw (band saw won't do in this case...) and finish with files. Take the unit and compare it make sure it's right and file it until it fits. If you are not planning to make them recessed then the template is optional just drill the holes for the stud and insert them and shim the neck pocket for the angle needed, if it's set neck or neck through you have to recess them. I am doing this on a finished guitar (it was a retrofit from wilkinson) so cover the entire lower bout with blue masking tape, then mark for your mounting holes and drill them on a drill press. Make sure you err on the tail side when drilling holes so the unit doesn't come too far towards the neck and interfere with the pickguard or whatever (it will come forward a bit due to string pull anyways) and position the unit over the hole (if you can insert then remove the stud insert it to get an accurate representation of the unit) and position the template over the unit and when satisfied mark the position (or mark where the unit is and place template over that). You may affix the template with clamps but I used double stick tape making sure it does NOT move at all. Use a 1/2"x 1/2" template bit route the front ledge about 1/4" deep or about 6.35mm (this is from the measurement on the floyd rose website), the back ledge should be almost 1/2" or 11mm or so. Doesn't need to be dead accurate anyways. After that remove the template (I had to reposition the stud holes several times... be sure to err on the tail side), insert the stud and install.
If you do not have the required tools (laminate trimmer, drill press, appropriate bits, and templates) then either get the tools (you will use them for other guitar builds anyways) or have someone competent do this. If this is a particularly expensive/irreplaceable guitar then definitely get a competent professional to do this. If it's a vintage strat or whatever sell the guitar then make a new build... you will devalue your guitar if you do this! You may buy the template if you feel up to it or make it yourself... I did because NT to dollar exchange sucks and I am trying to import as little as possible.
For the nut end I actually used chisel and files for it because I don't know how to jig a router for this operation and a slip means an unplayable neck. You get better control with hand tools but it isn't going to look as good. I have seen people build boxes or whatever and jig their template bit over that but for me it was too risky. Anyways once you get the ledge made by whatever means, checking depth as you go (if you go too deep it's fine, you can shim it) You will use the appropriate nut and line it up good and drill the holes (they are all different do not drill anything until you have all the parts in your hands!) and the back counterbore if necessary. You will need a drill press for this operation.
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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.
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