With the nights drawing in, sitting in the garden without some form of heater in the evening is starting to become less appealing. Combined with an abundance of wood as a result of the several trees I felled this summer, building a log burner seemed like an excellent idea. I decided to base it on an old 7kg gas bottle that was lying around; it’s a nice size and shape, and made of thick, good quality steel that won’t burn through easily.
Before taking power tools to a gas bottle it is vital to ensure that there is no gas left in the bottle. Simply releasing the pressure wont do; you must remove the valve then fill the bottle with water to displace the remaining gas. The bottle should remain filled with water until all the gas has dispersed and then emptied and left to stand to allow any remaining traces to dissipate. After all of this, the bottle will still smell of ‘gas’; this is to be expected, the smell is caused by an additive that leeches into the steel.
I had a rummage around for something to make legs out of and came across 3 mini fence post spikes.
The bottom part of the spike is constructed from 2 tapered pieces of angle steel welded corner to corner. I cut these off just below the join with the box section, and ground most of the welds away. I could then then split the spikes into their separate parts with a hammer and masonry chisel.
In order to make the burner more portable, I opted for removable legs. This was achieved by cutting some tabs from a piece of the box section of a spike, into which I drilled and tapped M8 holes. I marked up positions on the bottle to weld the tabs on, and stripped the paint ready for welding.
Using my MOT welder (which I’ve made a few improvements to, detailed in an upcoming post), I welded the tabs on.
To fit the legs, I trimmed the tops and drilled bolt holes; seeing as the gas bottle now had legs, I removed the bottom stand ring (again, using the angle grinder). The box section pieces of the spikes looked perfect for a chimney, so I cut a suitable square hole by dropping the angle grinder directly down into the bottle.
At this point, I had something that looked like a log burner; to make removing the paint easier, and see how well it worked, I fired it up. It lit nice and easily, using a bit of newspaper and some split pallet wood.
While it did burn well, the chimney didn’t draw as well as I’d hoped. The first thing I did to improve this was to simply extend the chimney; I welded the box section of the third spike on the top for something like a 60% increase in length.
I also improved the mounting of the chimney onto the main body. Previously it had simply been pushed in, and held in place by friction; this was both a bit precarious and the extension into the body interfered with airflow, which reduced the draw. I welded on a couple of small plates with holes in, and used an old tent peg to pin the chimney in place. It still extends into the body to ensure a secure fit, but much less than it used to.
Another issue I discovered was that, while the legs provided excellent stability side to side, the burner was able to fall backwards too easily to be safe. I solved this by adjusting the legs and tabs such that the legs extended out backwards; in order to maintain the height I simply bent the tabs inward, using the leverage of the attached legs.
I also built a cowl to prevent rainwater filling the stove when left outside; I cut a piece from the handle ring and crushed it in the vice to increase its curvature, then bent some coat-hanger wire into a couple of supports. Welding the wire was a somewhat dubious affair; my welder is much too powerful for this type of job, resulting in welds that only just hold and are very inaccurate. It does work, but I plan to revisit this and do a better job once I’ve sorted current limiting on my welder.
All that remained to do this point was to apply a coat of paint. I used wire brush attachments for the angle grinder and power drill to remove the original paint; this took a long time as both gas bottles and post spikes are designed to withstand rough treatment outdoors.
I then applied a couple of coats of stove & BBQ paint, left it to dry then fired it up to cure the paint. I did have an issue with a bit of the paint around the fuel/air hole and chimney flaking off, but I suspect this is where flames were licking it due to building the fire far to hot (with the help of a little bit of engine oil). I cleaned these areas with a wire brush and reapplied paint and have not had any more problems. The paint on the legs won’t have got hot enough to cure, but this does not seem to cause any problems; it looks and behaves just like standard black paint.
The new chimney draws much better, and there is no longer any risk of the burner falling over backwards. Once a decent bed of embers is built up, it works very well; the wood burns pretty cleanly, and what smoke there is gets drawn up well. It currently makes a very nice patio accessary, with the potential to make a good shed heater in the future.