How to punch a closed hole

 From:  Michael Gibson
4564.4 In reply to 4564.1 
Hi Rich_Art, also looking at your shape you've got another problem which is that the little piece that you're trying to union on is just a single surface with no thickness to it at all - that won't be possible to union on to the hole because it won't make a proper solid since there would be no thickness to the object at all in that spot.

In order to make a proper object there you would need to extrude that little piece you're trying to union to have some thickness before it would be able to be unioned on to the other solid and make a proper solid result.

Really for a case like this instead of cutting a hole and then partially filling it in with another piece it's probably best to initially cut it with an extruded cutting object using boolean difference with the cutting object not going all the way through, so it's all done after the first boolean.

- Michael