We have a good customer who is a regular in our brick and mortar store come in today and he got to talking with Tom Marsh (one of our pipe restoration guys) about his pipe. He has a nice billiard with a large bowl and hand-cut cumberland mouthpiece, but always has difficulty with the draw. After taking a look at the pipe and performing a pipe-cleaner test (just to see if there was blockage), I noticed that the airway at the button was just really small.
Nearly all hand-cut stems are chucked up in the lathe and drilled from the tenon side nearly all the way to the button side and then a smaller bit pops through. When I make a stem, I use a tapered 5/32" bit for the first inch or two (depending on the length of the stem), continue with a tapered 9/64" bit about 3/4" from the button, and continue through with a bit slightly smaller than 1/16". This small area gets widened into a V-shape before it’s filed slightly larger which allows for a thin button and comfortable airflow. Regarding our customer’s pipe, I could see a partial V-slot, but it didn't extend all the way down. In the past we've fixed this kind of problem by chucking up a bit in a hand drill, throwing safety to the wind, and concentrating while holding our breath. Luckily, we found use #7 for our metal lathe: opening a slot.
By chucking up a drill bit that was slightly larger than 1/16", we turned on the lathe to a really high speed. I carefully held the stem in my hand, pushed it onto the spinning bit (spinning so fast it grinds more than it cuts), and slowly pulled up the stem at an angle to cut the sides to a V. While maintaining the integrity of the slot shape and thickness, and after rotating the stem and doing this from the other side, an open slot was made noticeable. Tom ran a pipe cleaner through the modified stem to clean it up.
I haven't seen the pipe since. From what I'm told, the customer is puffing away on it downstairs with ease for the first time since he's owned the pipe. While this is something I definitely do not suggest you try at home unless you have the proper tools and technique, quite a few pipe repair men, or maybe even shops, might be able to make your restricted pipes smoke better than they ever have.