wrote in message
...
On Thu, 23 Apr 2015 11:14:09 -0500, F. George McDuffee
wrote:

On Thu, 16 Apr 2015 11:04:10 -0700, wrote:

I need to put an o-ring groove in the underside of 500 1/4-20
flathead
screws.
snip
This just showed up in my inbox. They may have something in
stock.
http://tinyurl.com/pe2y3bm
Greetings George,
Thanks for posting the link but what I need is what I described in
the
first place. I appreciate all the advice about different screws but
the customer wants what he wants. I also was surprised that only one
person directly addressed the original question, the one about
geometery.
Eric

The original question was:
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 do the job. A straight
groove tool won't work because the sides of the groove are curved. I
have made tools like this before but this is a small one and I'm
machining 304 SS so I need carbide and only want to make the tool
once. So I think to find out what radii to grind the sides of the tool
can be determined by drawing the screw head with the groove in it.
Then extend the sides of the head until they meet. Then mirror the
drawing around that point. Then I can directly measure with the cad
program the two different radii of the sides of the groove. Am I
correct?
Thanks,
Eric

What's lacking is whether or not you can tilt the bit to the same
conical angle when you rotate it in the grinder and grind with a very
narrow wheel, to duplicate the changing radius of the tapered hole
(not that you may need to). The projected relief radius will be
different if ground with a wide wheel, parallel to the tool shank and
feed direction.

I don't know enough about carbide form tools to guess if the larger
working relief you'd get by just circular grinding to the small end
radius of the groove would support the cutting edge well enough.

This solid geometry problem is difficult to put in words.

-jsw