... would I cut from an attachment to raise it from F to G? I read online that about 4” equals a half step, but I wanted to double check before I started cutting.

If you have a euph on hand you could just measure the 3rd valve tuning slide.

I can now confirm that 4” will get you a few cents sharp of a half step. Which is perfect because I can tune it out a bit with the tuning slide.

Open Excel... Bb is roughly 111" 12th root of 2 is 1.05946..

So, to go from each note to the next.. Multiply the current length by the 12th root of two... So A is roughly 117.6 inches. Repeat for each half step (you'll notice the length of a half step gets longer as you add more length).

Compare the length of F (148") to G (132"). It is often easier to make tubing shorter than it is to make it longer. Cut carefully.

You can figure out a more exact value with air temp and speed of sound, this will get you within a 1/2" or so.

Cheers,

Andy