I've just finished the pipe shown above. In the process, I was spurred to write this quick article because I was happily listening to my audiobook ("The Sweetness at the Bottom of the Pie", a pretty amusing mystery) as I filed out the bit slot interior, checking every so often to measure the draw. I had recently been reading a somewhat technical discussion of optimal airhole sizes and it struck me that I never measure anything - Never have, really. This is the sort of thing that sets the lore collectors in a tizzy because they like talking in very detailed terms about such facets of a pipe, and what is right and wrong and so forth, but I really find the "truth", in this case, to be so malleable that I've seen no need for rules set in stone.
The key is (in my opinion) not in any specific size but in the feel of the draw. I approach it from an intuitive perspective, not a scientific one. Some pipes have odd bends, flatter bits, thicker bits, unusual internals, etc, and the draw needs to be adjusted accordingly. This is the kind of thing I do on the fly - Gnerally I'll start with a 9/64" airhole for most simple shapes, or a 5/32" airhole for anything bent or more complex. But for me, the most crucial aspect of getting the internals right is not in doing complex mathematical calculations of internal CFM and velocity, but in getting the feel of it right. That's almost a microcosm of how I work in general. Shaping a bit and the bit slot is a probing process to me - I start out small and widen it, then test as I go... First, will it pass a cleaner easily? That's the first hurdle. I don't like pipes that I have to fight to get a cleaner into, so I keep some spares on hand and check the ease of the passage as I'm drilling.
Once the bit will pass a cleaner, the next step is for it to feel right. Yes, there's that F word again... And in 13 years of fulltime pipemaking, I have yet to find a better method, because I don't want the draw to be too open any more than I want it to be too restricted. Restriction is the obvious foe, of course, so that's what I work at first - I just use hand tools to widen the V slot until I gradually enlarge it enough that I can draw through it easily. The perfect draw, for me, is effortless but controlled - Where one can just barely inhale to bring smoke easily through the stem, without it being so open that there's no resistance whatsoever (That's usually a recipe for a hot-burning bowl and too many tobacco bits in the mouth).
My deepest apologies to anyone who saw the post title and rushed in hoping for detailed technical specifications that would render a great smoke if followed by rote, but alas, I can only write from personal experience. And that experience is that every pipe is different - Sometimes, a bend or a stem material or a different drill bit will create something unexpected, and even though the specs match what should commonly work on a pipe of that sort, it doesn't... I'll test draw from it and find it's oddly tight, and need to get in there and do some opening. Touchy feely? Perhaps, but this is one of several areas of life where I've found that my intuition provides me with better results than my logical thinking side.
