Hi Mark, it looks like there is a little tiny thin area connecting the 2 pieces together in this area here:





As best I can tell, the sloped in cutting pieces were possibly not quite fully aligned in that one spot there.

It's possible to remove the inner piece by selecting some faces of the model and then using the regular Delete command. To select a face, click on the object a second time - the first click will select it with "whole object" selection, and then when you go mouse over the object some more you will see edge and face sub-objects selected. Then when you click on it a second time you will then select an edge or a face. In this case you want to select faces, and click on the pieces of the inner part that you want to remove - once you have them selected (it's easiest to do this a few at a time usually) then push the Delete button or the Delete key on the keyboard to remove those faces.

Edges have selection priority so if you have your mouse close to an edge, the edge will be targeted and not the face - when that happens it means you have to zoom in some more so you can find a good area to click on the face that is not right next to an edge.

So anyway, that's the process you can use to just eliminate some faces from a model.

The problem will be after you're done eliminating all the inside faces there will be an open hole in that little area where the cuts were not quite fully aligned and where the pieces used to be connected to one another, and you'll probably need to build a surface to fill in what will be an open hole there.

- Michael