If this is for any type of production, have a machinist make a steel
block measuring about 3"x3" with a height of about 1". Then have the
machinist drill into the side of the block, a hole the size of the
tube, and as deep as about twice the length of where you wish to
place the hole.
Then, measuring the length of tube, and where the hole should be,
have the machinist drill a very small drill bit guide hole through
the top of the block in the correct place, (perpendicularly),
through the tube sized hole. Voila! You stick the tube in the tube
hole, hold it with your hand or a clamp, and drill through the hole
in the top of the block, through the tube. Perfectly placed hole in
the exact same spot every time. Great for placing rivets in tube
shaped necklace fasteners.
I use a set up like this for drilling holes to put rivets through
tubes to hold materials I want to stick into the tubes in place.
Sounds complex in writing, but its not. If you need a diagram,
e-mail me off list. If its not for production, then others no doubt
have better suggestions than I.
Lisa, (Drove to Long Beach to see a new exhibit of 19th century
portraits of African Americans. It was really great!) Topanga, CA