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Kontiki Cone kiln by Michael Williams

Kontiki Cone kiln by Michael Williams.

DIY Charcoal Unit

I’ve put together some photos of a charcoal unit I welded together from two standard sheets of 2mm mild steel plate at 1200 by 2400.

This is a copy of the Kon Tiki style kiln and I followed the dimensions given on their web site with a few simplifications, because if you don’t have a workshop and several trained gorillas you aint gunna bend 2mm sheet into  a cone


Figure 1 The Kon Tiki dimensions from their web site

The next best alternative I could think of was to mark the sheets as if I was making a cone, but then divide the sides into an octagon so that the only bending I had to do was “straight”.

Mark your sheets as per the diagram below (ignore the 11 lines across the cone section the computer decided to add them) , divide top and bottom arcs into 4 sections ( so 8 in total on two sheets) and join the dots.

I’ll add a note here – it pays to make a scaled cardboard mock-up first if; like me; it’s been a long time since maths classes

On such large arcs I had no problems staying close enough on line with an angle grinder, and I clamped angle iron across the sheet as a guide for cutting the end edges nice and straight (but leave plenty of metal at the ends for joining the sheets together)

To bend the 8 sides I “scored” down the lines with the grinder and a clamped straight edge, and then keeping the straight edge clamped you can bend the sheet quite sort of neatly. From some scrap wood I cut a 22.5 degree reference to get the bend at the right slope

Kontiki Cone kiln by Michael Williams.


Figure 2 A standard 1.2 by 2m mild steel sheet marked for one half of  a cone (ignore the 11 printed lines)

First time bending will only be approximate at any rate.

To strengthen the sheets and to fix the angle more accurately I cut 30cm lengths of 2.5 cm angle iron and welded them across the bends at about 20cm down from  the top edge.

You can now weld the two sheets together; a sledge hammer is quite adequate for those minor adjustments that will probably be needed at this point.

There was enough off cuts to enclose the bottom of the cone, at which point I also added a 1 inch pipe inlet (that’s what was on the scrap pile), but I recommend putting in the biggest pipe you can.

I also welded back along the score cuts I had made to initially bend the sheets, just to fill them back in.

The block of land that my wife and I manage is very steep, and my design criteria here was the unit had to be portable: manageable by two people; it had to be “tippable” and have a hose connection for convenient quenching.

To this aim I welded two lengths of old water pipe (38cm) on either side(58cm up from the base) to act both as arms for carrying the unit and pivot points for the trestle legs; also made from old water pipe, when time came to empty it.

kontikiocto Kontiki Cone kiln by Michael Williams.

Figure 3 Portable charcoal unit plus base (Kontiki Cone kiln )

Kontiki Cone kiln by Michael Williams.

At this point I just welded as much angle iron around where the arms joined the sheet metal as seemed necessary, it started to buckle at one point as I filled it with water so I welded some more on the inside

The trestle legs worked as planned, but as the unit would probably be approaching a ton in weight when full of water and charcoal I fabricated a portable base as well.

In operation the base takes all the weight, and adds more stability, once the water has drained and the unit is lighter the trestle legs slide onto the arms, the portable base is kicked away and the unit is then able to be dumped in a matter of minutes. Doing it this way i.e. with the legs and base as separate units, makes the whole thing more portable


Figure 4  the front leg of the portable base for the Kontiki Cone kiln.–


Figure 5  Just kicks out of the way

The portable base by the way was cobbled together from an old bed frame.


Figure 6  Kontiki Cone kiln. Fits nicely on a ute.

full of biochar Kontiki Cone kiln by Michael Williams.Figure 7 At this point the portable base is taking all the weight, the legs are more like outriggers on a canoe; we live on the side of a hill!

on-its-swing Kontiki Cone kiln by Michael Williams.

I hope you have enjoyed the Kontiki Cone kiln by Michael Williams. Please leave comments below and Michael Williams might be able to answer your more specific questions.



{ 3 comments… add one }
  • clemente September 15, 2016, 9:35 am

    ok From italy

  • Raymond Orenda October 25, 2016, 7:24 pm

    Looking forward to learning more about biochar to help me empower our community too!

  • Curtis Rock April 21, 2017, 9:06 am

    I like the minimal welding and minimal bending. What gauge of sheetmetal do you recommend to use to balance the tradeoff between strength, ease of welding, cost, and ease of bending?

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