| Add an STL check to the top of the stack for your model and then use it to check for errors. If you have any errors then you should fix them as the STL check is looking for things like double and open edges, both of which will break a boolean. If there are no errors then try cutting the hole in one side, using a slice plane to cut the object in half down the middle and then removing the side that doesn't have the hole in. You can then use Symmetry to complete the model
If you are still stuck, PM me the model or a link to it and I'll have a look at it |