I would form a piece of flat stock.
In a piece of IPE (ironwood) use a router with a ball end tool to form
the female die.
Use a round over bit to form the male punch, with a little clearance.
Place SS sheet over die and C clamp forcing SS into the female die.

Machining off half of a SS tube is a real PITA, and you will likely
find that the residual stress in the tube will cause significant bend
in the machined part.
Dave

On Jan 20, 9:54 am, lens wrote:
we got a stainless steel farm style sink in the kitchen. There's no
counter edge on the front of the sink so any splashes that land on the
sink deck run off the front edge onto the floor. For a pretty
expensive sink, it's not a good design. My idea to fix this is to get
a 3 ft "half round" of ss tubing, maybe with a 1/8" or 3/16" radius
(1/4" to 3/8 diam tube before slitting) and fill the inside of the
half-round with silicone and glue it down to the sink deck just to
make a little "speed bump" to stop the water. I figure if the edge is
straight, then there should be no glue visible. Of course the problem
is how to get or fab this. Any ideas?