I recommend using a square to set up the cut off tool, and also make sure the tip of the tool is very square and sharp. On larger lathes using much stiffer cut off tools, it is often good practice to widen the kerf by working on the side of the cut to prevent chips sticking.
Nicely explained, I would encourage beginners to not try to completely part off, just go in enough to break it off by hand. I always tap the part to get it off, this prevents damage to part and operator, which is important if the part has threads. You are much braver than I, to be using a HSS blade, I only use carbide inserts which don't rub on the sides. I use small cnc lathes so the lathe is enclosed, I would expect to part aluminium of that size at around 3000rpm, but that may be hazardous in an uncovered manual lathe. Good Video!
