Brian,
The most common hatch sealing surface is
flat, with an o-ring in the center of the hatch sealing surface. The hatch
o-ring grrove must be machined in such a way that the o-ring will not fall
off. Normally this is done by precision milling the groove with one of the
walls angled so that the top of the groove is slightly smaller than the radius
of the o-ring.
An o-ring handbook will have the
information with all the dimensions to machine the groove for the selected
o-ring material and durometer.
Hugo