On Fri, 17 Apr 2015 09:58:38 -0400, Ed Huntress
wrote:
On Fri, 17 Apr 2015 08:53:27 -0500, jim "
wrote:
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 think its a poor idea to make a round groove normal
to the surface. A square cut like the crude profile drawing
below will perform better. O-rings are not all that precise.
cutting a groove that tries to match the shape of the o-ring
invites trouble and won't work better than a square groove.
When O-rings are under pressure, a possible key to shaping the grooves
is the way the pressure will be applied. In the job shop I worked in,
we made ball-and-socket fittings for electron-beam guns that were used
in vacuum chambers, and the O-ring grooves had to be a tapered wedge,
from one side to the other. The vacuum sucked the O-ring into the
shallower side of the wedge.
The o-ring will be sealing against low pressure-basically water a few
inches deep. So the sealing cannot be helped by pressure or vacuum and
instead must rely solely on compression. The customer would rather use
stock o-rings that are available everywhere.
Eric