Monday, July 06, 2009

New centerboard (part 8) - Failure becomes success

After failing to melt lead with a propane torch, I went looking for stronger tools.

Many instructions say to use a campstove to melt the lead. You want to be outdoors so the fumes don't collect (where do they go?). I didn't want to buy a new campstove for just one use, so I searched for used ones. There aren't many around. I finally found one at Marine Exchange, a used boating goods store. The salty old guy there suggested I use a weed burner, instead. It would produce a lot more heat, which meant I could melt the lead faster, using much less fuel. It took him 10 minutes of searching to find all the bits I would need: a hose with a regulator, a fuel switch, and fittings to adapt between each. Most of that time was finding the right combination of fittings. $10 for the set.

He also suggested a coffee can as a crucible, and vice grips to pick it up and pour. When I felt how heavy the cast iron pan + 11 lbs of lead was, I decided to get a coffee can. Who buys coffee in a can any more? I think most people buy it in plastic or fresh-ground in paper. It took a while to find one, but eventually I tried freecycle, and someone delivered it to my door. (Thank-you!). I didn't have vice-grips, so I decided to use 2 large pliers.

I borrowed a propane tank from a friend, and enlisted the help of my father-in-law who was visiting.

The block of lead was too big to fit in the mouth of the coffee can. My father-in-law said that a hacksaw would gum up easily with lead, and suggested a different approach. We used a hammer and a prybar, and perforated down the center. Flipped it over and repeated. Then leaned it against a concrete step and wailed with a sledge hammer, at which point the lead bent and we could pull it apart and put it in the coffee can.

We got all the propane hose bits hooked up, with Teflon tape between the fittings, and soap water to look for leaks. There were a lot of parts! Here's the setup, ready to go:

We fired up the weed burner and pointed it in to the can. The breeze blew the flame away from the can, so we made no progress fast. We moved in to the garage, with doors open for ventilation, and tried again. After 10 minutes we saw lead at the top melt, drip down, and freeze at the bottom. It looked like it would take a long time. I was getting tired of standing there holding the weed burner, so we turned it off and looked for a new plan.

Filled the propane tank up, to make sure there'd be plenty of fuel. (6.9 gal for $17). Went to the local general store for a camp stove, and found a basic model for $22. It was listed as 10,000 BTU, although I suspect those numbers are as much marketing as anything else.

I saw that it would screw in to the propane bottle that came with my little torch, but I was worried that there wouldn't be enough fuel for our job, and wanted to use the big tank instead. We looked through the set of fittings they had and picked one that seemed like it would work.

The next day we hooked up the camp stove to the big propane tank, went to light it, and got nothing. No fuel was coming out of the stove. We noticed that the small propane bottle looked like it had a pin on it that could open something on the stove's fitting, and figured we needed something more complex to push it. At the hardware store we found a different fitting that didn't just adapt to the right thread of for the camp stove, but included the little pin that we thought was missing. The hardware store also had a hose with the left-threaded fitting on one end, for a big propane tank, and a "throwaway" fitting on the other end for the camp stove. It was exactly what we needed, but at $42 I passed.

Back home we put the new fitting on, hooked it up, and again got nothing. *sigh*. After further pondering, we figured that there were two regulators involved, and that might be the problem. One built in to the hose, sitting right on the propane tank. The other in the camp stove's tubing. I guessed that they interfered with each other, and that stopped it from working.

We removed the regulator on the hose, and saw that it had different threads on each end. That meant I needed another adapter. I also saw that hose end was left-threaded, and there was a small adapter between it and the regulator.

We loaded all the equipment in to the van and drove back to Marine Exchange to find the right fitting. After 10 minutes we found two fittings that, together, would do the job. Drove back home, reassembled, and got leaks. Lots of leaks. We eventually figured out that one of the new fittings was really meant for plumbing, not for propane, and wouldn't seal well with the other fittings. Also, two of the fittings that should have worked together were leaking a little.

Here's the full collection of fittings:

We went back to the hardware store, and looked for alternative fittings. After 10 minutes of pondering, I decided to spring for the $42 hose that was exactly what I needed, instead of a cobbled-together collection of many parts that kept failing me in different ways. I wanted to get the lead melted already! I also picked up a pair of vice-grips, because having them securely clamped to the can seemed safer.

Put the lead in the coffee can on the stove, and turned it on. After about 1/2 an hour it was all melted. I used a cheap metal spoon from the thrift store to skim off the junk on the top. Poured it in the mold, saw it bubble and settle, and then let it set.

After it cooled I took it apart, and examined the result. The lead had pulled away from the edges all around, up to 1/8". It had not flowed over the tops of the screw heads; they probably cooled the lead quickly and were too high and thick. The bottom was relatively smooth and shiny, while the top was rough. During the bubbling stage, some tiny splashes of lead had left little bits sitting around, which we collected for later use.

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