Briar/Ebonite and the Weather

[d6monk]

Hi everyone,

I was wondering what your experiences have been with stem/shank junction and tenon/mortise fit changes over different temperatures and humidities and what you do to minimize these changes. Sometimes its tricky to get a good tenon fit and a flush stem/shank junction w/ no ridges over a wide variety of different weather conditions.

I always imagined that an decrease in humidity and/or an increase in temperature would make a tenon fit tighter, but sometimes things don't seem to follow what I think--what have your experiences been? Also, I always let the briar sit for a bit after drilling before I fit a stem to it to help minimize any changes down the road, but is there anything else I could be doing?

Thanks a lot!

Edit: fixed typos

[LexKY_Pipe]

In my experience briar appears to be very stable in humid or dry conditions. Perhaps its the way the briar has been cured. I tend to make the tenon/mortise connection a tad on the tight side. Figure it's easier to remove material later than to try to make a loose fitting tight.

[m.c.]

Humidity makes the fit tighter. I'm not sure of the effect of temperature. Just a conjecture - higher temperature (assuming humidity being constant) may loosen the fit because wood expands at a faster rate than rubber.

Another factor to consider is the compressibility of wood. I've noticed that a tenon which is turned right after the block has been drilled and fits on the tight side usually loosens a bit when subsequent shaping and sanding are completed. I think that's because during the process of shaping and sanding, the mortise wall is somewhat pressed down by tight contact with the tenon. Therefore I cut the tenon to give a fit a bit tighter than I expect on a newly bought pipe as allowance for the compression effect.

For those chunky shanks I prefer a tighter fit as there is less chance of cracking. It's the slim shapes that really make me boggle. It has to be rather precise with much less leeway, otherwise the fit will either be sloppy slippy or scare me with the horrible squeaks on insertion.

Edit:

On second thought I find the temperature conjecture doesn't make sense. I'd like to believe the effect of temperature change is negligible unless it's accompanied by humidity change.

BTW, the rough handling during shaping and sanding compounds the compression effect on the mortise wall.

[d6monk]

M.C.--I imagine that an increase in temperature would make the tenon fit tighter since from what I can find the thermal expansion coefficient for hardened rubber is about 20 times that for a typical wood. Also, I imagine that an increase in humidity would make the tenon fit looser since the wood (including the hole) expands with increased humidity. But like I said before things don't always go how I think--I guess lots of other effects (compression of mortise and/or tenon; different expansion/shrinkage in the tangential, radial, and longitudinal directions in the wood; different expansion/shrinkage in different parts of the wood; uneven absorption/loss of moisture on the inside and outside of the mortise; etc.; etc.) are in play.

I just wish I could drill a hole, make a tight fitting tenon and a flush shank/stem junction, and forget about it.

Anyone else care to share their observations/opinions/techniques/etc.? I'd love to hear them, this has been a problem that has been bugging me for a while .

[m.c.]

The thermal expansion coefficient for hardened rubber really surprised me. Lack of knowledge about coefficients was part of the reason I retracted my conjecture about effect of temperature.

However humidity, in my experience, tightens the fit. Please note that when the shank expands from moisture, the outer diameter of the shank does not change much, but the inside layers swell much more than the outer layers since moisture mainly penetrates shallower part of the wood. The result is an inward squeeze. This explains why we're often warned not to unplug the bit too often while smoking.

Previously I posted about unintended slight taper of mortise. It also makes the fit a bitch. I've noticed that the more cylindrical the mortise (assuming the tenon is perfectly cylindrical), the more comfortable and durable the tenon fit is, because it spreads friction and pressure along all the length of the mortise rather than concentrating at certain points. And it facilitates a smooth insertion with the right resistance, which is key for both overall tightness and avoidance of over-pressure at some points.

[Leus]

I have a customer that lives in one of the most dry zones of the world. Some of the pipes I sold him got loose tenons a week or so after they arrive to his home.

I solved this by drilling the stummel and let it rest for a week or so before fitting the stem. I don't think this has happened again.

Regards,
Leo

[Tyler]

To offer one anecdote:

I went to Dallas a few years ago and it rained the whole time I was there. Here in Midland, it is typically very dry. My pipes went from maybe 25% humidity to 100% for a few days.

My stems would literally fall out of some pipes. (Presumably those with the loosest fit to begin with.)

After returning to Midland, the stems fit were fine again.

[Sasquatch]

Where I live, the humidity is like... zero. There isn't any. And stems on a lot of pipes I buy seem tight after a little while... I pretty often take a little material out of the mortise or off the tenon, depending.

Opposite to this "dry makes loose" conjecture is the repeated finding of smokers that pipes which they ignore tend to have a loose tenon, and if they smoke the pipe a few times, it tightens right up.

So the fact is.... I just dunno.

[d6monk]

Well it looks like we are about back to where we started . Thanks for the replies guys, I really appreciate it!