The Charcoal Forge (first attempt)

[adpsimpson]

Hi all!

New hobbies needed due to quarantine madness, and forging is something I've wanted to try for many years.

A simple place to start seemed to be turning a file into a knife. I had a suitable hardened, high carbon, blunt old file, so needed a forge to anneal and harden it.

This was the (not very pretty) result. Based in an old steel 10" cake tin & £10 pot of fire cement, with a length of electrical pipe for air (connected to a hairdryer via a large paper cone, not in view).

The size is awkward - not really long enough and too deep. I had to heat the file in 3 sections (each end, and the middle). Also the high sides all round mean I can't hold it level in the heat, so one end will always be hotter than the other. I think I need to cut a notch at one end, so I can lay something down along the line of the air pipe.

I used a magnet to judge the temperature, which worked well.

 

 

 

 

I then shaped the knife blank using various tools: angle grinder, files, belt sander, sharpening stones, sandpaper. Whatever was to hand.

Now, a couple of photos of the closest this knife came to finished. The blade was quite thick, and there are no holes for rivets. The epoxy didn't take well (I guess I didn't clean the residue from the used engine oil quench well enough), so I had to remove the scales and re-anneal it to drill holes in the tang. At the same time I  thinned down the blade a little:

 

  

 

Then to practice rivets. I didn't have any rods of soft metal available, so practiced peining mild steel from various sources, in strips of wood of similar thickness to the scales. Although I managed some, I also split the wood just as often, so decided to defer that, and ordered some brass rod on the internet.

Finally, to re-harden it (second time). Sadly, at this point, things went wrong. I must have got the forge too hot, and melted / burnt the tip of the blade. 

So, re-annealed (3rd time), re-shaped the blade to shorten it, then re-hardened it (3rd time). That time, either in the forge or quenching, the blade warped. After tempering it I tried to straighten it but it snapped.

So, after all that, I've learned a xxxx of a lot (modification to forge needed to make it shallower, drill holes in the tang early in the process, don't quench in used engine oil, charcoal can get hotter than it needs to be very fast, etc), and feel ready to tackle the next file with confidence! Now to source some old files.

 

[Glenn]

There are several safety issues with your project.

EMT electrical metal conduit is galvanized. This is bad as it releases zinc fumes when heated.  Zinc, galvanized, and coatings

Used motor as a quench agent is bad.  Use other oils or a quenching fluid.

The forge is the wrong shape for the metal length you are using. It needs to be a long forge. The depth of the fuel needs to be much deeper so the metal rests in the sweet spot of the fire.  Look up the Tim Lively washtub forge. Tim is a member of the site and is very helpful in answering questions about his forge design.

Using a magnet to judge the temperature will get you close to the A2 point.  This may not be the proper temperature for forging.  The quenching temperature and quenching process depends on the alloy of the metal used.

A hairdryer connected directly to the forge is way too much air.  Leave an air gap between the hairdryer and the connection to the forge.  Aim the hairdryer more directly at the connection for more air, not so directly for less air.  Fuel does not make the fire hot, air makes the fire hot.  Use only enough air to produce the amount of heat you need in the forge.

Rivets can be made from many suitable materials.  

Welcome to the site. Others will post with more specific suggestions.  Check back early and often as the information can be posted quickly.

[adpsimpson]

Hi Glenn, and thanks for the advice. Much appreciated.

All but the galvanized pipe I had already figured out in the process of this first trial-and-error project - I'll replace that with something more suitable when I upgrade for the next attempt.

For the process of annealing / hardening, the magnet worked surprisingly well - the steel was soft enough to work easily after annealing, and as hard as the original file after hardening. I guess that, for the stage I'm at, that is sufficient?

It's funny, isn't it, how used motor oil is recommended in many places on the net. I've read through the topics on this site, after finding it pretty bloody awful in use (messy, flash ignition, awful scaling on the metal, a strong desire to remain up wind of it), and certainly wouldn't use it again.

The hairdryer was not directly connected, but I was obviously not controlling the heat correctly, hence the melted blade tip.

I had a good hunt around the garage for material for rivets, but genuinely couldn't find anything other than steel. I've bits of brass, copper, and aluminium in various shapes, but not pins. I though brass would work better, and look good, so have ordered that - what would you recommend for a wooden handle?

[Glenn]

You looked around the garage and did not see copper wire 12 ga or grounding wire, aluminum electrical wire, copper pipe, brass pipe, brazing rods, aluminum nails, copper components in electrical panels, etc.?  Ok maybe your garage does not have all of the above available. (grin)  It does not have to be a round pin, just something that you can use to form into a round pin.  The electrical grounding wire is 1/4 inch in diameter.  So you either need a larger hole or need to stock reduce the wire.  And where was it written that the holes had to be round?

Why not use those scrap pieces of damascus for pins?

Do not build a box so you can then think outside the box.  If you do not build a box, anything then becomes a possibility or opportunity. 

 

[ThomasPowers]

Well having started with a home built charcoal forge 39 years ago, what I would say is that your forge is a bowl when it needs to be a round bottom trough.  You don't need to cut a slot in the tin as you DON'T want to get the blade down near the air input---that tends to decarburize and burn it up...   You want a deeper fire so the blade can be stuck in the neutral to reducing zone.  By building up the sides with clay to make a more U shaped firepot you can get the depth without wasting all the charcoal to the sides.  That tin should do fine for small stuff---if you build up the sides.

Of course you didn't need to do any of that to make a knife from a file.  You can take a file and draw temper on it to get to what you want the final temper to be and then just find it from there taking care to not let it heat up during grinding. As I recall instructions for doing it that way were in the Last Whole Earth Catalog published in 1971.  Note that you want to temper the tang softer than the blade; so tempering the whole piece in the kitchen oven to the knife hardness and then temper the tang further with a torch and the knife blade stuck in water works.

[adpsimpson]

2 hours ago, Glenn said:

And where was it written that the holes had to be round?

Good point. That would make using random bits of stock much easier actually - I'll have to try peening square pins. I've got various bits of aluminium I could use for that.

 

2 hours ago, ThomasPowers said:

By building up the sides with clay to make a more U shaped firepot you can get the depth without wasting all the charcoal to the sides.  That tin should do fine for small stuff---if you build up the sides.

That's excellent advice, thanks. I'll do exactly that, still have some of the fire cement left so I can use it. However I see lots of people here just using plain old clay from the ground. Can sub-soil type clay from pretty much anywhere work, or do you use / buy a specific type?

 

2 hours ago, ThomasPowers said:

Note that you want to temper the tang softer than the blade; so tempering the whole piece in the kitchen oven to the knife hardness and then temper the tang further with a torch and the knife blade stuck in water works.

Actually I was trying to achieve the same but in the other direction - I annealed the whole thing, then after shaping I heated and quenched the blade, but not the tang. Then tempered in the oven. Would that work too, or is there a reason to harden everything and then further temper the tang?

Thanks for the advice, I really appreciate it. Planning to take another stab at it this weekend.

[ThomasPowers]

Well when I lived in Ohio, I used to drive a few miles to get to a clay bank I liked in a local creek. When I lived in Arkansas I'd source red clay from around where I lived. Here in New Mexico I sometimes use old adobe bricks or I get the "mud crack plates" from when a rain storm has filled the arroyos and then left puddles to dry.  I have friends who have used cheap pure clay kitty litter, unused please!

So in my experience anything "clayey or clayish" seems to work. The adobe comes "premixed" and is easy to work with and common around these parts.

Some alloys in thin section will air harden when they will not in thick section.  If the tang is not reaching critical temperature it should not be a problem---but you notice I was talking about  making a knife without hardening a file again and just going from the "as it stands" hardness where you need to draw it back for a blade and even more so for a tang.

[adpsimpson]

17 hours ago, ThomasPowers said:

Well when I lived in Ohio, I used to drive a few miles to get to a clay bank I liked in a local creek.

That's a good idea actually. There's a few little creeks around here, I'll check their banks to see if the mud is more clay-like.

[pnut]

Try this. I used one for about a year and was very pleased with it's performance.   https://www.iforgeiron.com/topic/44842-just-a-box-of-dirt-or-a-simple-side-blast-forge/ 

Pnut

[Donal Harris]

“Red clay” = Just about any soil in Oklahoma except in the eastern parts. 

[bluerooster]

Red Clay= dirt in Georgia.   

[ThomasPowers]

I went caving in NW Arkansas once and came out with my bluejeans red.  No chance of bringing them to the laundromat they were so bad. I waited till we had a terrible thunderstorm and then went out and beat them on the street---we lived at the base of a hill and water would flood down the street when it rained.  It left 2 block long "blood stains" but I was able to bring the jeans in and get them washed.  

[Donal Harris]

There is or was a company in Oklahoma that was dying t-shirts with Oklahoma red dirt. It can be rather hard to get out. 

[ThomasPowers]

BTW this is the basic reason we had "red barns".  Iron oxide was the cheapest colour to add to linseed oil to make paint so large structures were often painted red.

[adpsimpson]

Loving this conversation about clay - wasn't expecting that when I posted.

As an update, here are some snaps of the next knife I've made, using stock removal from 3mm O1 steel, with a beech handle. I hardened the blade using an update to the forge above, taking most of the advice into account. Much easier process, due to the improvements and the steel.

The peened brass pin for the hinge isn't holding enough tension to keep the friction high enough. I've ordered some phosphor bronze bushes, which I'm going to tap to accept countersunk bolts in the next one. Overall though I like the shape and feel of the knife, and the O1 is incredibly easy to work with.

 

  

 

[ThomasPowers]

ADP, have you ever seen the examples in "Knives and Scabbards, Museum of London"?  (Around knife number 309 and 310 IIRC)  Handy if you want to go a bunch of centuries earlier in configuration.  I made one using the original type of wood---boxwood and carved out the slot using a sharpened square cut masonry nail mounted in a scrap wood handle like a sen.  Beeswax finish and if anything it's a bit hard to get it out.

[adpsimpson]

Thomas, thanks. I can't find an exhibition from the Museum of London by that name, is it this book you're referencing? If so I'll buy a copy - nothing like a good read during lockdown.

[Commercial link removed]

 

Edited May 19, 2020 by Mod34
Commercial link removed per TOS

[ThomasPowers]

Yes it's a book and rather rare in that it has so many examples (over 300!) of medieval blades in it; all shown in archaeological drawings done to *scale*.  Much clearer than just pictures and if you have access to a good copier you can increase the copy size to get them back to 1:1 scale.

There are also metallographic write ups on some of the blades and finally a nice range of extant leather scabbards showing the tooling done on them .  

These are basic EDC blades; it's amusing that with over 300 examples, all are single edged IIRC.  They are also not the usual museum fodder of fanciest found; but more a good collection of everyday using blades over various centuries.  (With information like what types of wood were used for handles.)

If you make any items for the re-enactment crowd; there are a lot of good ones to replicate all nicely dated and from a known locale.