depends on the length of the tenon also
You can make all the shoulder cuts using the miter guage and fence together as you said, no problem. Now how do you waste away the rest of the material? Tenon jigs are meant to be used holding the piece vertically and passing it over the blade. Like this:
You can only make it as long as the blade will raise above the table.
Holding the piece vertically can be a bit of a balancing act as well.
I make my tenons using a bandsaw using stop blocks on the fence for the tenon length. like this:
They can be made any length that way, rather than be limited by the raised blade height and it's easier with the work being horizontal rather than vertical.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 11-23-2013 at 05:54 PM.