On Thu, 16 Apr 2015 13:29:50 -0700, etpm wrote:

On Thu, 16 Apr 2015 13:25:17 -0700, wrote:

On Thu, 16 Apr 2015 11:04:10 -0700, 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 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
I know it's bad form to reply to your own post but I obviously need to
make a clarification. The groove is going into an angled surface and is
normal to that surface, not to either the axis of the screw or the top
face of the screw. I alread know I need a 5/16" dia o-ring. But since
the groove is normal to the angled face the sides of the groove will
have larger radii than the radius of 5/16".
Eric
I know, I know, replying to a post that is a reply to my own post is
really bad form. Makes me look weird, like jon banquer. Anyway, after
looking at the groove drawing I know I am correct. But please feel free
to correct me if I am wrong. And don't tell banquer that I am replying
to my own posts, he might think I'm like him.
Eric

Here, let me break up your string of self-replies (I don't know if you
resemble Jon or not -- I've had him plonked for years).

Man, this is so damned confusing. Can you post a picture someplace? So
you're making a grove in the angled part of a flathead screw, so you can
slap an O-ring on there and seal to aluminum -- yes?

And the grove will go in normal to the face, which means that as the
groove gets deeper, the radius of the grove gets smaller -- yes?

And you want to make a tool with JUST ONE TRY, to make it all work -- yes?

Dayum -- you're a brave man.

Why can't you just turn a straight section in the screw head, a hair
larger in diameter than the ID of the O-ring, and just the right depth to
accommodate the thing when the screw is tightened? Then you can just use
a standard insert. It'll look like a shoulder on the screw head. Unless
you have some compelling reason for the screw head to capture the O-ring
(and **** off anyone trying to get one out without damaging it), wouldn't
this meet your stated goals?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com