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What cutting tool i need to use for a long ID chamfer?

I have no experience of programing or operating cnc, but lots in the manual field.
Could you not have the boring bar angled to 45 degrees and have it fed into the job at 45 degrees (like a conventional compound slide would do).
That way, the 0.375" boring bar will probably clear the 0.250" hole when it just finishes cutting the desired taper.
Yes, that should work, if the radial circle under the cutting edge does not rub below the Cutting edge.
Likely one could hold the boring bar at 45* against a radius gauge to eyeball that the BB heal and the insert clearance would miss.
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2. Chamfer method, where the cutting starts from the edge of the .250" hole. after a two cut my insert broke. (not the cutting tip but the opposite side of the cutting tip)
Not sure what you mean by chamfer method. Your boring bar is wrong for this operation. It will never get to the bottom of the chamfer without hitting the other side with the back edge of the tool.
You need something like this, (the tool at top): t_369_m_01.jpg Then you can face out from the .25 hole and not hit the other side of the chamfer. Since you're cutting aluminum, you could just grind a piece HSS to emulate the above bar.