Hi jason, yes like lyes mentions scaling down is your best bet, because probably there is too large of a gap between those edges to be joined and if you scale down it scales down the size of the gap hopefully within join tolerance.

So the process works like this - select the model and then run the Transform > Scale command.

At the first prompt that says "Pick origin point" type in 0 and push Enter, that will specify 0,0,0 as the scaling origin. Then at the second prompt type in 0.1 (as you type your numbers will go into the "Scale factor" field) and push Enter, that will then scale your object down by 1/10 in size.

After you are done with the join you'll repeat this process to scale back up by typing in a 10.0 scale factor at the second prompt instead.

Then with the scaled-down model, select the face that has the 3 naked boundaries on it and use Edit>Separate to break it apart from the main model, then select the pieces and use Edit>Join to join it, then test for naked edges and see if there are none. If that did not work, try going down another 1/10 in size.

If that still does not work, then you may need to do some repair work on that surface, if you select all the boundary edges of a surface you can then hit Delete to untrim the surface and recover the full underlying surface, then retrim it to the surrounding pieces. That can help if there is anything wonky in those edges like if they are mangled up or badly formed somehow.

Also if you want to post or e-mail your current joined model to me I will try to help you get it joined together.

- Michael