How to make a hole in a part

[Omnomc]

Here’s the part (it goes through the whole of the Baseplate as you can see in the image below):

When I Negate and Union it to the Baseplate, it does this:

I would like it to create a hole that goes all the way through the baseplate like this:

[alpharetzy2 (alpharetzyfake2)]

Try making the height of the negate part exceed the bottom baseplate height