To improve my distillation capabilities, I wanted to increase the length of pipe from the spout of my alembic to the receiving bottle. Fortunately I had some pyrex tubing in the garage and it turned out to be nearly the right diameter.
So to enlarge it I rounded off the end of a piece of wooden dowelling, heated the tube with a blowtorch and applied the dowelling to it.
Which sort of worked, the problem was getting a good distribution of heat with my small blowtorch. Turning the tube helped, but ultimately I wasn’t able to heat it all the way round and apply the dowelling properly.
So glass blowing or pyrex glass manipulations is harder than it looks. Here’s what I ended up with though, the tube widened just enough to fit onto the spout: