If I were you, I would redesign the tooth rest so that it can rotate concentrically with the spindle, and graduate the mounting in degrees. This allows for clearance to be set for different diameters on end mills when grinding the OD. just lowering the tooth rest to achieve the same result causes binding of the rest on the flute of the cutter. This is how Harig's air bearing fixture is designed. I use it for all my end mill sharpening on my #1 Norton cutter grinder.