Primary Supports - Ball Cutter Question

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Original poster: Yurtle Turtle <yurtle_t-at-yahoo-dot-com> 

I bought a ball cutter from McMaster Carr, in hopes of
being able to machine my primary supports. I'll be
using my radial arm saw to do this. I was hoping to be
able to cut slightly lower than the middle of the ball
into the supports, so I could snap my tubing into
place. The problem is that the ball cutter I bought
apparently can't cut more than half way into my
supports. This means that I'd have to make two passes,
in order to get the depth I need, which would result
in a slot, rather than a partial circle. In other
words, I won't be able to snap my tubing into place.

Now on to my question...

Do ball cutters exist that would allow me to cut
deeper than halfway down in a single pass? If so,
where can I get one? (A cheap one.)

thanks
Adam