Just by the way, most pre-formed tapered stems will not have a straight line from tenon to bit.
Now I will start working the button. First it is rough shaped on the 25mm beltsander and then fine tuned with files and nailfiles, until I'm satisfied with the shape.
Then the rest of the stem follows. Depending on the condition of the stem at this stage, I start with sanding in either 220 or 320 grit. If I did the job well, most cases will start with 320 and then work up towards 400 grit. Sanding above 400 grit is a waste of time, because the tripoli I use (and most other guys, I think) have a grit of 400.
For the 5mm or so just in front of the button, I use nail boards. Just with sandpaper you just can't get that bit sufficiently smoothed.
And here is the stem just before polishing. Every millimeter has been sanded and smoothed. Ebonite is a bit of a bugger and polishing might just reveal a little scratch or indentation that was missed, and it might just be that you have to go back and repeat a step or two.