On Thu, 16 Apr 2015 14:00:53 -0700 (PDT), whit3rd
wrote:

On Thursday, April 16, 2015 at 1:18:27 PM UTC-7, wrote:
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 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.

I wouldn't do it the hard way, with a groove in the head. I'd make a square
tool cut in the head, and another (end-mill) square cut in the seat,
to make the correct size 'box' for the as-compressed O-ring.
It might be best to use an O-ring that seals against its inner and outer
circumference, those are the easiest dimensions to control.

Holding the screw while making the cut can be ... challenging. Maybe
you'll be threading a soft collet?
I need to make these for about 25 cents each in quantities of 500. I
can do that with only cutting a groove in the lathe. I can't cut the
seats econimically. Besides, cutting a groove normal to the angled
face is an accepted way of using O-rings, I have done it before, just
not on the underside of the part. I am not sure if I will be using a
soft collet. I may end up having to face the whole underside of the
screw head, but I really want to avoid that because of accelerated
tool wear and I don't want to use two tools. I may be able to come up
with a horseshoe shaped device that lets me locate off the angled
surface and then I remove the device and press start. I will most
likely use a dead length collet closer in the lathe.
Eric