Yesterday I finally figured out how to make the groove for the binding in a proper cheap-skate way : I disassembled a cheap chinese router-bit with ballbearing and calculated what circumference the proper ballbearing would have to be. I then asked a friend of mine, who happens to work at a metal-shop, to make two ' tubes' with that circumference, and with exactly the right hole in the middle to fit on the router-bit. Point is that it is not a ballbearing, so it will leave some marks on the wood, but I reckon I can fix that with some sanding.
Reasons to choose for this solution:
1) I think paying a lot of money for a router-bit that I will only use once is a waste of money.
2) StewMac sells router-bits that have an american size axis, that will not (properly) fit my european router. I would then have to spend even more money on an adapter to make the US-size bit fit my EU-router. In the best case that would be unneccesarily expensive, in the worst case expensive and ending up with a bit that does not fit well in my router.
3) fiddlling about and making your own tools and solution is nice......
Left: the torx and the old ballbearing that came off the router-bit. Middle: the router-bit without bearing of tube. Right: two tubes of different thicknesses made exactly the right size.
The results is very good I must say: the binding is exactly flush:
Disadvantage is that I will have to do some more sanding on the guitar to remove the scratches the routerbit has left. You can very clearly see the scratch that one tube has made in the wood, but in my opinion this is quite easy to correct, so I'm happy with the result.
So the next job is now to sand the purfling and binding (their shape is not exactly square, so I will have to sand to make them fit better) and glue them in the grooves. Hopefully that won't take as long as figuring out how to rout out the binding-groove has... ;-)