How to taper the tenon

[souljer]

Hi,

I know this is an old thread, but it speaks exactly to several issues I've been wondering about.

Here people are talking about a chamfer or taper in the tenon as a way to reduce moisture.

I thought moisture was caused (in part) by condensation created by a change in the diameter of the smoke-hole. So it was desirable to have the mortise and tenon meet exactly so that no gap was between them and the smoke hole was one continuous channel all the way to the bit.

This way the smoke comes out of the mortise and enters a slightly larger gap before being funneled back down the smoke hole in the stem; would that not be a radical change in diameter? Also would this cause the smoke to cool off slightly, creating condensation? What happens when the smoke is blown back down into the bowl -gently of course- now it's going to run into the flat side of the mortise?

I don't understand how this prevents moisture. I have seen a Rodriguez pipe up close and took it apart; I was stunned to find the tenon and mortise with mirroring large, wide, tapers (<>) forming a small open space within the shank! With all that going on, how can the pipe not create excess moisture?? If I remember correctly it did look pretty wet and sticky in there. Is this just a way to avoid the gurgle sound?

Now that I think of it, does smoking my cob without the filter do the same thing? I mix a special blend of my own; an aromatic that I make with tobacco and lavender (sweet taste, beautiful room note and all natural -no casings or chemistry), but it smokes hot if I'm not careful. The other night I was out working and smoking and it was cool. I thought the new cob's filter was cooling off the smoke. Later when I took it apart I found that the filter was not in the pipe! Was this empty space cooling off the smoke? However wouldn't this radical change in smoke-hole diameter cause moisture and a wetter smoke?

...or have I completely misunderstood everything I've ever read in my entire life??

Sorry for the long post, but I have so many questions and I've been working on making my own first pipe for over a year and have still not done it. Hopefully the one I'm working on now will be it (I say that everytime of course), so I'm wondering about these issues as I get to the mortise/tenon again (still without a lathe).

Thanx for all your help and advise so far (on the site). It's really a great resource.

[alexanderfrese]

As far as I remember some postings on some German websites made by Rainer Barbi, who seems to be a real freak about physical concerns of the airflow, it is highly important to avoid turbulence within the airstream.
Optimal solution would be the "One-Piece design" used (if not invented) by Random on some of his pipes. The whole airway has the same diameter over it's way, so no turbulences will occur until the smoke is on the smoker's tongue.
As for the basics of thermodynamics, every widening of the airway on it's way from bowl to mouthpiece will increase the chance for condensation, but expecially critical are sharp edges, that will cause turbulences, that will cause condensation – at least to some extent. Sadly enough, it all depends on lots of other influences, as well.
So every detail applied to the airway's construction that smoothens diameter changes (i.e. a chamfer in the tenon) should decrease the chance of condensation – though not necessarily makes a dry smoking pipe alone.

I am far from beeing some thermodynamic specialist, though the basic principles of thermodynamics bring lots of light to even the most simple but controverse social and human questions…

[Nick]

You are exactly right that turbulence is one of the major causes of a wet pipe. What happens is this. A laminar, or non-turbulent, smoke stream moves in concentric layers. Each layer runs paralel to the others and as you move away from the pipe walls, speed increases. Tiny droplets of moisture are naturally suspended in the smoke stream. In a laminar flow these droplets move along in a nice orderly fashion. A turblent flow is chaotic and random. The layers of the flow cross and swirl, causing the tiny droplets to crahs inot eachother, making bigger dropplets. Eventually the dropplets get bigg enough and fall out of the smokestream.

The dregree of turbulence is measuered by the Reynolds number (Re). You can do an internet seach on this and find out all sorts of cool info. The higher Re, the more turbulent the flow is.

In my opinion, Random was really onto somthing with his emphasis on airflow. Avoiding turbulence is key to a clean cool smoke (heat disapaits quicker in a laminar flow btw.) However, the basic design of a pipe invariably creates turbulence. The biggest generator of turbulence in a pipe is not the tenon/mortise juncture. Rather is is the point at which the draft hole enters the tob chamber. This junction not only radically changes in size, but changes in direction too. There are at least two ways to ameliorate this issue. First, the more forward the bowl is canted, the less turbulence is created. second, by rounding off the sharp edges of the draft hole enterance, alot of turbulence ca be avoided. There may be other solutions too. I'd love to hear what else folks come up with.

[StephenDownie]

I'm still waiting for someone to invent a self-heating pipe where the entire pipe and stem warms up to prevent moisture from condensing out of the smoke onto the cooler airway.