MetalworkingFun Forum

With a bonfire, just leave it in the fire and dig it out a few days after the fire goes out. "few" depending on how big the fire was.

We had a small bonfire yesterday, I put the two small offcuts in there so when I get a chance I'll dig them out and try drilling. If it looks promising, I'll put the larger pieces on the big bonfire pile- we do an annual burn of our pile of fallen branches etc and the bonfire is usually big enough to stop traffic. If the stuff will anneal, that should do it.

I've melted iron in charcoal, so if it's a really roaring bonfire, maybe not the center of the coals in the inferno to play it safe. I think heating to a dull red in the coals near the edge of the fire would be plenty. Then just rake the ashes over if it gets exposed toward the end.

Dull red worked on my piece anyway.

You just need to get it above the Curie Point, which conveniently is when it ceases to be magnetic.

I walked past the little bonfire heap this morning and one of the test pieces was sitting on top of the ashes where the breeze had left it exposed, I couldn't resist the temptation of retrieving it and giving it a trial run.
It was still just a little warm to the touch, not much higher than body temperature. I put it in the drill press where the same 6.8mm twist drill that could barely scratch it the other day was still in the chuck. Drilled through it like butter! Followed it with an 8.5mm drill then power tapped it (thanks Tom!) with an M10 spiral-point tap that arrived from eBay a couple of days ago for my toolholders. First time I have used one of these taps and I don't know how I'll ever go back to my straight-flute hand taps now.
[attachment=14395]
In the photo, just to the left of the tapped hole-about an inch from the tap at about 10 o'clock- you might be able to make out the little dent that was all I could manage with the drill before the annealing.
Looks like the shaper table extension project will be back on track after we burn the big pile. I might wait until it has burned down a bit before I put the steel on, although once it gets going it tends to be very difficult to get close- will see how we go.
I put the test piece back in the embers to finish cooling off, just to be on the safe side. I'll be very pleased if I can make this stuff useable by annealing like this, as well as the shaper extension I have in mind a couple of chuck mounting plates as well.

Excellent result :)

(05-04-2017, 01:28 AM)awemawson Wrote: [ -> ]You just need to get it above the Curie Point, which conveniently is when it ceases to be magnetic.

Once that fire's going, I won't be getting near it with a magnet- or anything else- for about 10 hours. Will take it on trust!

There used to be a type of gas fired metal heat treatment furnace made by Wild Barfield (or some similar name) that used the magnetic effect by having the sample effectively as the core of a transformer, the windings being presumably embedded in the insulation of the walls. As the transformer effect of the core ceased the gas was modulated to just keep it hot.

The magnet test has never worked for me, regardless of the size or thickness of the fridge magnets I have tried. They all just melt and run off, and then burst into flames.

Plonker !