Part 4: Heat Treating the Blank

The wood fly rod project continued this past weekend with heat treating of the rod blank. Heat treating is a critical stage in rod build process; it hardens the wood and gives the blank an overall stiffer and faster action.

The first step is to put the rod blank back into the rod drying jig (see Cutting and Drying the Blank) – this will serve as a make-shift oven, and hold the blank straight as it is heated. As before, hose clamps are used to hold everything together, but unlike the initial drying process where the hose clamps were placed every 6”, this phase only requires a clamp every 12”.  The clamps should be just snugged down enough to hold things straight. Too much tension and you risk leaving depressions from the conduit compressing the heated and softened wood. Then the entire set-up needs to be placed in a position where at least a third or so of the drying jig can be heated at any one time without melting or igniting anything.

 

To heat the entire set-up I prefer to use an electric heat gun – the type typically used to strip paint. It is not as quick as a propane torch but the heat can be more accurately controlled and there is less chance of scorching the wood (something you definitely want to avoid). You will need to heat the metal conduit and enclosed rod blank to a core temperature of ~ 450°C, and keep it there for several minutes. Because the drying jig will cool slightly between passes of the heat gun, you will need a heat gun that can generate more than 450°C (on the high setting, mine goes to 540°C).

The set-up is heated one 12” section at a time (if you try to heat a longer section than this the jig will cool too much between passes and you will not attain a high enough core temperature). Pass the heat gun back and forth along the conduit, working around the circumference of the section, with the nozzle almost touching the tubing. The goal is to gradually bring the tubing and the wood to temperature without generating any hot spots (even with the heat gun it is still possible to scorch the blank). You will need to spend about 20 minutes on each 12” section at the butt end of the blank, 15 minutes per section in the middle, and 10 minutes per section at the tip. As things heat up you will smell a musty, woody smell and you may see steam coming off the blank– this is normal. If you detect a burning smell, things are getting a little too hot. Ideally you want to gradually work the entire length of the blank in one session (about 2-3 hours) starting at the butt end and working towards the tip.

 

Some minor scorching is acceptable but
you do want to avoid over doing it

There are two things going on during the heat treating process. Firstly, although the rod blank was dried for a full year, there is still some moisture remaining in the wood due to the average ambient humidity in the air; heating the rod blank drives out this residual moisture. Second, the intense heat breaks the chemical bonds between the polysaccharides and water molecules found between the wood fibers. As the water molecules are stripped from the intercellular polysaccharides (part of the “glue” that holds the wood fibers together), the wood becomes harder – resulting in a stiffer, stronger rod blank.

With the weather looking more winter-like this weekend, I will likely spend some time sanding the rod blank to the desired taper.