If you are talking about retaining a bearing in a plate and you don't expect significant axial load (which you shouldn't with ball bearings), another approach if your hole is not small enough is to "stake" the bearing in place.
You stake it by using a pointy punch (gee Ken thats awful technical) and indenting the plate just outside the diameter of the hole. This pushes enough material into the machined bore to help retain the bearing. You might want to put indents at 3-6 locations around the hole. I would NOT use this method if the bearing is seeing any axial loads.
The advantage of this is that you don't need a press. The disadvantage is that you are hitting your nicely-machined and partially-assembled parts with a hammer.
Regarding press-fits: it is possible to do some relatively simple calculations to determine the theoretical holding power of a press-fit. Although, asking an experienced machinist is usually quicker....
)
Ken