On Thu, 16 Apr 2015 12:44:38 -0700 (PDT), whit3rd
wrote:

On Thursday, April 16, 2015 at 11:00:16 AM UTC-7, wrote:
All-
I need to put an o-ring groove in the underside of 500 1/4-20 flathead
screws. So I need to make a groove tool ...
... to find out what radii to grind the sides of the tool
can be determined by drawing the screw head...directly measure with the cad
program

Dude, coffee isn't enough, you need sleep.
To seat an o-ring, you get the groove dimensions from the manufacturer of
the o-ring.
And to seal a 304 stainless screw head, a soft copper gasket makes more sense.
I guess I wasn't clear in my first post. The o-ring groove is going
into an angled face and the groove is normal to that face.
The customer wants an o-ring. We discussed this. The screw bears
against aluminum. And his customer needs to be able to replace the
o-ring at will. Soft copper washers are not as near as common as
o-rings.
Eric