Hi, I have only been working with mazatrol for 2 weeks but have just been on a course this week for the new matrix control which was taught using the 640MT control manual so its quite similar. I dont know which control you are using but I'll tell you what I know and I have a programming manual with B axis in as a reference.
On the control I was using I clicked line machining then used the "/Y" option, in this it will ask usual questions and one question will be what angle you want the B axis to be. Then it asks shift points in Z and R. If you were to say produce a 45 degree flat with the bottom of the flat on the front face you would set the Z shift to be 0 and the R shift to be the bottom of the flat where it meets the front face. The X position will be half the distance of the flat then you set the line to go from something -60 to 60.
Try clicking face machining, then slot and pick either the /C or /Y option and then answer the questions from there. If the /C or /Y options are not there unfortunately I cannot help you as I said I have only been working with them for 2 weeks.
Hope this helps