I have noticed that if a pipe sits for a while in a humid enviroment, the stem fit will tend to loosen, and conversly, if a pipe sits in a dry enviroment, the stem fit tends to tighten.
Has anyone else observed this? It is just the opposite of what I would have expected to occur.
Mike
Stem fit vs humidity
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Tyler
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random lines the mortise with Ultem.JMB wrote:random wrote:
"so I make them so that the briar does not touch the stem."
Say what, you lost me. Doesn't the stem touch something. Has too, so would it not have the same problem at another part.
Mike,
I have experienced the same thing you describe. It shocked me when it first happened. I have seen it over and over since then though, and now have no doubt in my mind that it is the case. Here is a post I made to ASP about a year ago:
What continues to surprise me is the number of folks that will stick there pipes in the bathroom and run a hot shower in order to steam up the bathroom and "tighten" a loose stem. It makes things worse, yet folks continue to recommend it. That is strange, me thinks.I have had many conversation on this topic, and I'm sure more to come.
It is an interesting debate.
My experience matches Jack's: humidity will increase both the OD and ID
of the shank resulting in a looser fitting tenon. Being a pipemaker in
a very dry climate, it is an issue that I am constantly concerned with
because almost all of my pipes will end up in a more humid environment.
Here is an interesting link I found the last time I entered into a
conversation on this topic:
http://www.physics.purdue.edu/demo/3A/e ... _ring.html
Obviously this experiment deals with different materials and reason for
expansion, but I think the principle is applicable to our situation.
Anecdotally, my experience agrees.
Tyler
Tyler Lane Pipes
http://www.tylerlanepipes.com
http://www.tylerlanepipes.com
Tyler,
The Purdue experiment is interesting for two reasons.
Although the physics involved are quite different, a valid parallel can be drawn between the thermal expansion properties of a metal ring, and moisture induced expansion of a wooden ring.
Secondly, we intuitively accept the fact that an increase in temperature or moisture will expand most materials to a predictable extent. The value of that experiment is understanding that these changes in temperature/humidity, dimensionally affect a solid object differently than a ring, or in our application, a hollow tube.
Many of us have observed that by moistening the mortise of a pipe, the tenon fit tightens considerably.
Unfortunately, this only reinforces the notion that an increase in humidity will tighten the stem fit.
In practical application, a hollow wooden tube will absorb moisture from the inner surface as well as the outer surface, and both the inner and outer diameter will increase. This can easily be demonstrated by soaking a briar shank in water overnight. The stem fit will noticeably loosen.
Again, in a practical application, this may not be apparent in a completed pipe until the wood reaches the equilibrium moisture content, usually a period of many months.
I don’t know what if any value there is in being able to predict this increase or decrease, and there are so many variables involved, that any attempt would have to include a large margin for error.
Having said that, and to appease my masochistic instincts, I crunched a few numbers, using average values of radial and tangential expansion, moisture content, changes in relative humidity, density, and a bunch of other variables.
Based on average humidity variations across the U.S. the average change in the diameter of the mortise would be 6%, which translates to .0022”
I’m not sure if all of this one finger typing really explains the what’s and why, and I think that our time can be more effectively utilized in determining what we as pipemakers can do to lessen the effects of humidity on our creations.
Mike
The Purdue experiment is interesting for two reasons.
Although the physics involved are quite different, a valid parallel can be drawn between the thermal expansion properties of a metal ring, and moisture induced expansion of a wooden ring.
Secondly, we intuitively accept the fact that an increase in temperature or moisture will expand most materials to a predictable extent. The value of that experiment is understanding that these changes in temperature/humidity, dimensionally affect a solid object differently than a ring, or in our application, a hollow tube.
Many of us have observed that by moistening the mortise of a pipe, the tenon fit tightens considerably.
Unfortunately, this only reinforces the notion that an increase in humidity will tighten the stem fit.
In practical application, a hollow wooden tube will absorb moisture from the inner surface as well as the outer surface, and both the inner and outer diameter will increase. This can easily be demonstrated by soaking a briar shank in water overnight. The stem fit will noticeably loosen.
Again, in a practical application, this may not be apparent in a completed pipe until the wood reaches the equilibrium moisture content, usually a period of many months.
I don’t know what if any value there is in being able to predict this increase or decrease, and there are so many variables involved, that any attempt would have to include a large margin for error.
Having said that, and to appease my masochistic instincts, I crunched a few numbers, using average values of radial and tangential expansion, moisture content, changes in relative humidity, density, and a bunch of other variables.
Based on average humidity variations across the U.S. the average change in the diameter of the mortise would be 6%, which translates to .0022”
I’m not sure if all of this one finger typing really explains the what’s and why, and I think that our time can be more effectively utilized in determining what we as pipemakers can do to lessen the effects of humidity on our creations.
Mike
Hello all,
Im no nuclear designer or anything but one thing I do notice. I make a pipe here along the coast of California and the stem fits nice and tight. I will ofcourse pull the stem out when taking it home to Tucson for photo's. In Arizona I have problems fitting the stem because out there the fit is much tighter than California. Once I return to Cali the fit is as it should be.
Im no nuclear designer or anything but one thing I do notice. I make a pipe here along the coast of California and the stem fits nice and tight. I will ofcourse pull the stem out when taking it home to Tucson for photo's. In Arizona I have problems fitting the stem because out there the fit is much tighter than California. Once I return to Cali the fit is as it should be.
Greg Clemons
Random,
.002 is quite a bit of change, and will affect the stem fit noticably.
I have used Delrin for years, and although it allows for a tighter initial fit, it is not a cure all for this problem.
I usually drill the mortise to 5/16" diameter, but have been experimenting with both smaller 1/4" and larger 3/8"+ diameters to try to determine if this will help to reduce the effects of humidity change.
I would suspect that a matching tapered mortise and tenon would alleviate this problem, but I lack the equipment and skill necessary to accomplish this and validate this theory.
Mike
.002 is quite a bit of change, and will affect the stem fit noticably.
I have used Delrin for years, and although it allows for a tighter initial fit, it is not a cure all for this problem.
I usually drill the mortise to 5/16" diameter, but have been experimenting with both smaller 1/4" and larger 3/8"+ diameters to try to determine if this will help to reduce the effects of humidity change.
I would suspect that a matching tapered mortise and tenon would alleviate this problem, but I lack the equipment and skill necessary to accomplish this and validate this theory.
Mike