OK, to answer @EWilliams’s question (to which I’m sure he actually knows the answer ;)), how do you make something like this? I’m speaking somewhat abstractly here, but I think the following will convey the general concepts. It has taken me a couple of days to work it out, and who knows if this is how they made the original (certainly in every place where I refer to CNC below, it would have been just eyeballing stuff on a manual Bridgeport probably.)
Start by turning a rod with a ball-shaped end.
Bore out a hole
Using a CNC mill, cut out this profile (traced from reference images and calibrated for size) entirely through the rod using a long flat end mill. In order to get a close a possible to sharp angles up at the top, a final pass or two should be done with a very small radius end mill, like 0.25mm.
Taking a large ball-shaped mill, pass it in from the end of the part in a straight line parallel to the center axis of the rod until the midpoint of the ball mill hits where the vertical blue line is in the image below
Using a flat end mill, knock down this little slope
Make another ball-shaped end mill pass, this time coming in a line from the other direction and with a smaller radius mill.
Create another turned rod with ball end to insert through the hole on the needle. This one is coming up a bit too high (still working on it), but you get the idea.
Trace a profile for shaving off the side (this would be done on a CNC tracing along the bottom path with a flat end mill cutting at a right angle to the center axis of the needle). I got this profile from a photo of the original, which I and the person who shared it with me are unfortunately constrained not to share publicly.
Mirror features to the other side
Elliptical finger indents. Don’t ask me why they weren’t circular, which would make them much easier to machine, but the photos strongly suggest an elliptical profile.
Carve a bit off the top so that it’s not a perfectly circular profile (traced from Scott’s photos shared above)
A small through hole runs right down the middle of everything (again, from the photos I can’t share, but trust me.) This also helps with the way the air runs through the system assuming you plan to make one that hisses when activated.
You would then need to give this a firm buffing to soften the hard machined features, so it ends up looking more like this:
Rarely have I seen replicas that get even half of these little details right. It has been fun studying them so closely. So much so that I think I’m going to finish and do the whole body.