Re: How do you get the hollow centre in a hypodermic needle?

A hypodermic needle is made from stainless steel "seamless" tubing. 

First, a sheet of stainless steel is wrapped around a metal bar and welded 
along the overlapping edges to make a short, thick, solid tube.

Then, the tube is drawn through a series of dies, each one just a little 
bit smaller in diameter than the last. This reduces the diameter and wall 
thickness of the tubing and stretches it out into very long lengths. It 
also blends the weld seam with the rest of the tubing, making it stronger 
along the join than it would be otherwise.

Finally, when the tubing reaches the right size it's cut to length and the 
end is ground and polished to make the point.