Update: Wednesday, May 6, 2009

In this post:
1) Experiments in Heat Treating
2) Heat Treating My Sections

1) Experiments in Heat Treating

Once my oven was up and running, I ran several tests with various pieces of scrap bamboo. I wanted to be sure my oven wouldn’t completely ruin bamboo strips and I wanted to better understand changes in the bamboo before and after heat treating. Although the tests were far from scientific, I set them up in that manner.

Null hypothesis: There will be no observable/measurable differences between heat-treated and untreated bamboo strips.

Alternative hypotheses for testing:
1) The strips will be damaged or completely destroyed;
2) The string used to bind the strips will melt or become otherwise troublesome;
3) Straightened and pressed nodes will revert to their naturally crooked and humped shapes;
4) Moisture will be unevenly removed from the strips;
5) Two to three minute cook time differences will produce observable differences in enamel color/tone;
6) Differences in bend and elasticity of the bamboo strips will be produced;
7) Additional, unforeseen, difference will take place in the strips that will be identifiable in subsequent aspects of the rod-making process.

To conduct the tests, I heat treated lots of test strips in the pipe oven for various amounts of time and at various temperatures that ranged from what I gathered was way too little time and heat, to what was about the right amount of time and heat, to what simply had to be way too much time and heat. All and all, it ranged from a few minutes in the oven to nearly 30 minutes and from about 200 to 400 degrees. I bound some of the test strips with string (like the real strips will be) and I left some unbound. I straightened and pressed some of the nodes prior to testing and I left others alone. When I did straighten and press nodes, I monitored how long the strip needed to be heated by the heat gun before it became pliable. On a few of the test strips, I also took a few moments to find the point of equilibrium – that middle(ish) spot where the strip balances end for end since a heat gradient in the oven would extract more moisture from one end, producing a lighter end and a change in the equilibrium point. I also attempted to find the average point at which un-cooked test strips would start to crack and split when bent and compared that to the average point at which cooked strips started to crack and split. Finally, I just fiddled around with cooked and uncooked strips – planed them, bent them, examined their color, sanded them, heated them with the heat gun, froze them in carbonite, pressed them in the vice, waved them about wildly in my basement allowing them to flex hard, and I snapped a couple over my knee for no apparent reason.

A few strips that were sacroficed during tests


A completely unrelated picture of Solo encased in carbonite... he's quite well protected


Here’s what I learned from the tests.
1) The strips were not damaged or completely destroyed by the pipe oven unless cooked excessively (i.e. temperatures approaching and exceeding 400 degrees and times approaching and exceeding 25 minutes);
2) The sting used to bind the strips did not melt or become otherwise troublesome;
3) Straightened and pressed nodes did revert (but not always) to their naturally crooked and humped shapes;
4) Moisture was not unevenly removed from the strips (unless I purposefully worked to create a heat gradient by only heating one half of the pipe);
5) Two to three minute cook-time differences did not produce observable differences in enamel color/tone (even excessive cook-time differences failed to produce observable differences… perhaps due to the already dark flame toning of this rod);
6) Differences in bend and elasticity of the bamboo strips were produced (it’s a bit of an exaggeration but the strips were kind of like Tootsie Rolls before heat treating and more like raw carrot sticks afterward);
7) Additional, unforeseen, difference did take place in the strips that have been identifiable in subsequent aspects of the rod making process (a. re-heating nodes to re-straighten/flatten them takes longer after heat treating and makes them more prone to cracking/splitting, b. planing feels smoother and easier on heat treated strips).

All and all these experiments helped me learn a lot about the process and outcomes of heat treating bamboo. They also served to convince me that my oven was perfectly adequate for the task.

2) Heat Treating My Sections

Once my oven was designed, built and tested, completing this phase of the make was a breeze. I hung the oven, capped the ends, brought the temperature up to 350 degrees, inserted my first bound up section and cooked it until the steam stopped exiting the two small escape holes. I then removed the section, inserted the next section and cooked it up. And finally, section three went into the oven for its turn. All three sections took a similar amount of time to cook, between 12-14 minutes.

After nearly an hour, the aroma of propane and steamed bamboo was thick and intoxicating.


Next time we progress to final planing.