With the right setup you can do some metalspinning to alter the shape. Unless very crefully thought out you wind up with some very thin areas. The metal needs to be annealed to soften it and spinning will harden it.
I believe, but have no referances, that brass instruments are formed from sheet stock and the seams brazed and polished.
So you anneal it again. This method can work, if the form is something you can melt out again.
Yes, also some parts are drawn from seamless tubing. Techniques tend to be a combination of hammering, burnishing, spinning, and drawing, often with different makers choosing differently even for the same part. For example the bell section can be formed as a cone (possibly with an insert to complete it) and hammered to expand the flare and spun to shrink the neck, or you can spin a flat disk into the bell and join it to a seperate cone... Tapered tubes can be formed from trapezoidal sheets and drawn to size, or simply drawn down from tubing over a mandrel, using an annealed fender washer as a die.
The instrument industry does produce some parts by machining down and boring out barstock. Typically they like not to do precise cutting operations more than once, so it would be done with step drilling and a custom reamer, but CNC equipment both within the industry and at job shops is changing that.
One difference when machined from bar stock is that the material is likely then a leaded brass, C360 say, instead of the unleaded brass more common in tube stock C260, though some is a leaded C330. This has possible implications if the part is a mouthpiece and will not be plated.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.