Valve Seat Cutters

[Renaud]

Dave, 
my method is a little more scientific, I had a refaced valve diamond plated. 
A few rotations By HAND with a little paraffin and job done. Then grind in valves in the normal manner.

Same with the little Neway:



which is tungsten carbide.
Some manual turns only are enough. Very good finish and then I also use some paste grinding.
One has to machine the "pilote" which centers the 3/8" mill in the valve guide.

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As can be seen this 30 mm mill can be extended for larger valves.