I’m constantly amazed at pipes that smoke well. Actually, I’m amazed that so many of my pipes smoke well, and , at the same time, are comfortable and attractive. There are a multitude of ways that things could go wrong, that it’s pretty stunning when you realize that it doesn’t happen much more frequently.
If the drafthole enters the chamber above the bottom, the odds are that you’ll wind up with a puddle, and you’ll get a lot of gurgling. If the drafthole comes in a bit low, you’ll have a channel for the condensation to follow. Either way, it’s going to be a wet, sloppy smoke.
Another place that can be problematic is the mortise. If the mortise isn’t drilled deep enough, the tenon will bottom out, and you’ll have a gap between the faces of the stem and the shank. While this won’t affect the smoking qualities, it doesn’t look good. A much more common flaw is that there’s a significant gap between the end of the tenon and the bottom of the mortise. That gap will cause an interruption of the airflow, and when that happens, condensation will accumulate in the gap and the pipe will gurgle. What’s really bad about this is, unlike moisture in the bottom of the chamber, a pipe cleaner won’t remove it while you’re smoking because it puddles in the gap, and the pipe cleaner will pass by it without having the chance to soak it up. No less an authority than American pipe maker Todd Johnson says that it’s important to make the mortise just a hair deeper than the length of the tenon, because, if the fit were “perfect”, when the wood takes on moisture, the tenon will bottom out, and you’ll wind up with an unsightly gap.
The airway in the stem is another issue. If the drafthole diameter in the tenon is the same as the drafthole in the shank (which it should be), and it were to be the same all the way through, the stem would have to be way too thick at the button end. The way to avoid that is to step down the size of the airway, but that restricts airflow and promotes a number of problems. To dodge that bullet, the drafthole can be widened at the end. That’s why modern pipes are slotted at the button, but some pipes are better than others when it comes to slotting.
There’s a lot more to it than the simplistic way I’ve put it, and I have a hard time building a bookshelf, much less making one of these amazing feats of engineering. There are also other factors that are much more subtle that I wouldn’t understand well enough to discuss. I’m just glad that there are a number of very smart and talented people who can execute all of these things well, and for less than you would expect.