Making a mini furnace

Everyone needs a tiny furnace don't they?

I made this one to make blade forging more efficient than using the barbecue...
It's a steel box I found, with some marble inserts to create a thermal jacket inside it. The tube to the right is the column of an exercise that has been modded to create a way to blast air in to up the heat. Here, it is shown with a hot air paint stripper. This is OK, but isn't really pokey enough...

In practice, the air was blasted in from the front hatch. This was much more effective

Construction

The metal box I rescued from a scrap metal pile. The tubing is a section of exercise bike frame. The frames in exercise bikes are actually more sturdy than real bikes. This tubing is built for strength, not lightness like any real bike.

The hole in the original tube was way too small, so I reamed it out to the right size with die grinders

Till it matched the girth of the blower that would be inserted later.

For insulation, I used some offcuts of marble to create internal walls.

And the weirdness that is Vermiculate. This is super fluffy mineral granules that feel like polystyrene, but are not affected by heat.

This can be poured into the spaces between the metal and marble.

With a lid on top...

That's about it

In use, I used lumpwood charcoal.

Once lit, this can be fed in from the front. The flame is fanned with a hot air paint stripper.

Results

Here is an old cold chisel I bought for virtually nothing in a shop during a very lovely day. These are made of quite useful tool steel.

After heating in the mini-furnace, this took a battering on the anvil...

Until it ends up a like this. (this takes many passes)

The same chisel after a good hammering.

Once flattened out, the blade face was created by hacking it off with the angle grinder.

Voila..

This one is an old file.

It has been shaped with the grinder#

Eventually after a lot of grinding and polishing...

They become all shiny and lush like this

Before and after

A cold chisel and it's eventual chisel blade...

Triangular file and its eventual form...

The ones above are number 4 and 5 here.

Nice!