A Silly Millimeter

26th May, 2004: Posted by glpease in Pipes

For a long time, now, I’ve been working on pipes, when necessary, to improve airflow, smoking characteristics, moisture accumulation in the shank and stem, and so on. I have adopted, from my old race motor building days, the phrase “Polishing and Porting” to paint something of a picture of what these pipe modifications can entail. The comparison between a great pipe and a racing motor is not really that far-fetched. In an engine, proper airflow is essential to good performance. It’s impossible to extract those critical horsepower unless the right mixture of air and fuel can efficiently get into the combustion chambers, and the exhaust gases are efficiently scavenged once the go-juice has been burned. Restrictions in manifolds, poorly tuned headers, improper mixture settings, or mismatched combustion chambers or intake circuits will keep the engine from performing at its peak.

Okay, so the pipe/engine analogy is a bit of a stretch. A poorly tuned pipe won’t explode at 14,000 RPM, and the average smoker isn’t all that concerned by having every last molecule of burnable tobacco adequately converted into smoke and ash. Certainly, though, a great smoking pipe is a joy, and one that is fussy is, well, fussy. I don’t like fussy pipes, so, when I can, I try to fix them.

Enter a Castello Sea Rock, shape #33. This pipe is best described as a short, chubby Canadian. The exterior of the bowl is nearly pot-shaped, but the tobacco chamber is that of a billiard. I really like the shape. This particular pipe, however, presented me with one of the most difficult smoking experiences I’ve had. When I got the pipe, I filled it with a favored blend, and lit up. The draught was like trying to suck cookie dough through a soda straw. I figured I’d clogged the airway, removed the stem, poked and prodded the shank with a pipe cleaner, ensuring everything was clear, and tried again. No luck. It was challenging to finish the bowl, but what made matters worse was the almost complete absence of flavor throughout the smoke.

“This isn’t good,” says I. The pipe didn’t taste bad; it just didn’t taste. Further, when it was time to clean the pipe, I had a hard time getting even a thin pipe cleaner through the stem! I’ve seen narrow airways, especially in some vintage Castellos, but this was ridiculous. Something had to be done.

I measured the shank’s airway at ca. 4.2-mm, which is just about perfect, and decided to leave it alone. The real work had to be done to the stem. The stem is 59-mm in length, 12-mm of which is tenon. At the button end, the pin-prick that masqueraded as a draught hole was only about 1.2-mm. At the tenon end, things were a little better, with an internal diameter of about 3-mm; too small for a shank airway as open as this one. Inside the stem were two dramatic “steps” between sizes, indicating that three different drill sizes had been used to construct the airway. “Why didn’t they just finish the job?” I muttered.

The first step was to open the tenon with a tapered bit, with the hopes that this would also eliminate the first of the two internal steps. I chose a bit that tapers from 4-mm down to a needle-point, and drilled to a depth of 45-mm - sufficient depth to knock off the first step, and open the tenon adequately, but not so deep as to risk thinning the stem wall excessively at the tapered bit end. Inspection with my bore light and a little poking with pointy things demonstrated phase one to be successful. But, what about that damned 1.2-mm opening at the bit?

Grabbing my thinnest, finest, tapered round needle file, I started to work from the bit end, widening the “funnel” and slightly increasing its height. The result was an oval cross-section that I hoped would have approximately the same cross sectional area as the narrow part of the tapered hole I’d just drilled. (Clear as mud?) Next, working from the tenon side, I used the same needle file to smooth out what had been the second step in the passage, thus providing a smooth transition from wide to narrow, and a smooth flaring out to the “exhaust port.” During this whole operation, “flow tests” were conducted by blowing through the stem to check progress. The improvement was already significant.

One common source of the gurgling that “wet smoking” pipes can exhibit is the sudden transition from a wide draught in the shank to a narrow one in the tenon, especially if there’s a gap between tenon and mortise floor. When the smokestream exits the shank and expands in the plenum that is formed between shank and stem, cooling takes place, allowing moisture to condense. If the tenon’s inlet is too small, the increased velocity that results will tend to suck the condensate into the tenon, where passing air will cause the gurgle. I hate gurgle, so I worked with the needle file to open up the tenon still further to about 4.7-mm, ensuring that the transition along the airway remained smooth. Final testing on my “flow bench” (blowing through the stem) produced no whistles or other odd sounds. Almost there!

The final step involved rolling small strips of 400-grit Wetordry paper into little tubes, feeding them through the stem, and fine-sanding the airway to smooth out any tool marks the file may have left behind, and to eliminate any vestigial ridges that may have remained from the pre-surgery steps. After final sanding, I measured the tenon’s inlet at 4.8mm, which is sufficient to prevent condensation uptake from the 4.2-mm shank airway.

After a thorough rinsing of the stem, I reassembled the pipe, and returned it to the “flow bench.” Perfect! But, the real test would in the smoking. I filled the little beauty with the same tobacco I’d smoked in it before, and put on my “Critical Smoking Cap” to take the pipe for a test smoke. The result was remarkable. The pipe now offered an effortless draw, and delivered fantastic flavor! Success!

I’ve always believed that airway design greatly effects the way a pipe smokes, but have equally eschewed the notion that this aspect of a pipe’s construction has much bearing on the way it tastes. The outcome of this experiment, however, has converted me into a true believer. Next time I have a pipe that lacks flavor, I know the first place I’ll look. Some pipes may not respond as well to this treatment, but I’d rather give those bland briars a chance at a new life, than to just throw them in a box to be forgotten, or to foist them off on some poor, unsuspecting ebay buyer. I know some people consider the idea of modifying pipes as something akin to heresy, but I buy pipes to smoke, and if a little effort can make such a vast improvement, I make no apology for thinking I just might be able to help them fulfill their true destinies.