Old School Forging/hardning/tempering

I

Iamurruler7

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Aug 25, 2011
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6
Hey guys, im new at this and dont exactly have the money for an electric oven or propane/gas powered forges. i have taken an old air compressor tank and cut it apart to create a charcoal/wood old school type forge.

im looking for suggestions, tips, anything anyone can give me to help out, specifically anything on how to properly insert the blades into the fire/coals to get them hot enough and how to hold them or "soak" them at these temperatures needed.

i figure getting it to and holding it at much higher hardening temperatures such as those 1200+ would be easeir than say low temps like 400+-, but what if ineed to keep it at a temperature but below another temp? such as for tempering? i.e. say i need a blade at 450deg. for 2 hours, how do i get it to 450, keep it at 450, and stay there for that amount of time (just an example) or say i need a blade around 1500-1800 but not over 1800?

any help at all would be great,


Thanks
Neil
 
Couple of suggestions. One, practice. Temp control is the hardest part. Two, use the oven in the house, or buy a toaster oven for tempering.
 
Soaking a blade for any length of time at a particular temperature in a forge without temperature control is difficult at best. Your best bet is to use steels that will obtain proper hardness without having to hold at temp. during the hardening process.
Tempering in a forge is even trickier, the 2 hour temper cycle (repeated 2 times, usually) that most makers use is based on tempering in an oven, not a forge. A toaster oven or regular kitchen oven will work for tempering, you can pick up a toaster oven at Goodwill or another second-hand store for 10$ or so. If you are bent on doing it in a forge you will probably have to forget holding at temp for long periods, and use the oxidation colors as temperature indicators.
 
I'd strongly recommend 1084 for a starter steel especially when using a coal forge. It has probably the most simple heat treatment with no significant hold time needed, and it has one of the lowest critical temperatures at +/- 1450F which is pretty darn close to the curie point where iron turns non-magnetic at 1414F. This means for practical purposes, you can use a magnet to determine when you're getting close to temperature. Quenching for the thin profile of a knife can be done in canola (or brine if you want it faster and want to crack some knives :D). One of the things I've read about coal is that you need to be careful not to over-heat the thinner sections of a knife when heat treating, especially near the tip. So you have to figure out the zones of your fire. A baffle (edited: as Tai points out below, it's a muffle, not a baffle) tube (stainless steel tube) nested in the coals can help even out temperature fluctuations a bit when heat treating.

There's a ton of great resources out there for free on the internet which can help you get started.

--nathan
 
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One other hint. Learn about decalescence/recalescence. You can see these as sort
of shadows moving though the steel as you pass critical temp going up and down.
Once you learn to recognize them they can be more useful than a magnet.

Still, Nathan is right. Use 1084.
 
I-7
Where are you located? You can get a lot further along much faster if you can visit with a bladesmith in you area. It will save you a lot of time, effort and money...even if you have to pay him some for his time. There is a lot of science and physics involved in this activity that have to be understood on some level to get even mediocre results. You don't have to "learn it all", but you do have to learn basics to be consistantly successful.
Hammer-ins are also a good place to get your feet wet, learn and make contacts.....so take advantage of these events when possible.
The trouble you went through to cut up the tank and build the forge is just as complicated and time consuming as building a simple Lp forge. Just need to do your reSEARCH up front. Pace your desire to "get at it" and learn to "get it" first.

Believe me, I understand the want to "do it". It looks simple enough, but you need to know and understand what it is you are trying to do, if you don't want to be frustrated out your shorts. FInd someone close that can coach you along the way.
 
For tempering, you can make an "oven" type arrangement that sits over your coals. Basically, just a couple sheet metal baffles at the bottom, a sheet metal enclosure and a good professional grade oven thermometer suspended inside the chamber will work.

I recommend using a "muffle" for the hardening cycle.
 
... What I don't get is how buying a toaster oven is considered "old school"? LOL
 
Are you kidding?? Those things have been around for YEARS!! You must be a really old fart! ;) :D

I'm not sure if he's more interested in primitive forging/heat treating techniques or if he is just trying to get started with as little cash outflow as possible.

--nathan
 
Old fart for sure, but not that old. I think the first electric toaster came along in the early 1900s which is around the time of "modernism". I didn't come along until '57

I think he's trying to save money. Toaster ovens are cheap, but the elements are too close to the work and they don't hold a constant heat, but rather shut on and off. If you do use a toaster oven put a couple baffles in it or put the blades inside some type of muffle or both. Also use an oven thermometer. Don't trust the dial.
 
Something else that helps even out the temps in a toaster is adding mass. Putting a heavy brick or tray of sand in the oven and giving it plenty of time to get everything to temperature before putting the knife in will really help reduce temperature swings.

--nathan
 
silver_pilate said:
I'd strongly recommend 1084 for a starter steel especially when using a coal forge. It has probably the most simple heat treatment with no significant hold time needed, and it has one of the lowest critical temperatures at +/- 1450F which is pretty darn close to the curie point where iron turns non-magnetic at 1414F. This means for practical purposes, you can use a magnet to determine when you're getting close to temperature. Quenching for the thin profile of a knife can be done in canola (or brine if you want it faster and want to crack some knives :D). One of the things I've read about coal is that you need to be careful not to over-heat the thinner sections of a knife when heat treating, especially near the tip. So you have to figure out the zones of your fire. A baffle (edited: as Tai points out below, it's a muffle, not a baffle) tube (stainless steel tube) nested in the coals can help even out temperature fluctuations a bit when heat treating.

There's a ton of great resources out there for free on the internet which can help you get started.

--nathan
Click to expand...

Not sure what you mean by "nested" but, the system works better if the muffle is suspended over the coals. If coals are touching the muffle you can get cold spots. Also, form some type of insulation or refractory over the top to help hold the heat in and save some wood.

The muffle doesn't need to be stainless, but a fairly thick wall will help muffle the heat better. It could also be ceramic.
 
It almost pains me to suggest it, but you could always edge quench, quickly use a file to clean the edge to bare metal and then watch the heat bleed back into the edge from the hot spine...... edge... there, I just had to say edge one more time.. okay twice.

Keep a wet rag handy to stroke it along the edge so you don't lose the hardness completely.

A few things to know if you are using a forge...

Steel begins to show colour in dim light at about 1200-1300F
Steel becomes non-magnetic at 1414F
The ignition point of paper is about 450F
Water sizzles on steel at about 212F-250F
Water vigorously dances off steel in droplets at 250F-375F
Water pretty much explodes off of steel hotter than 400F
You can hold a piece of steel that is around 130F-140F but you'll be looking for a place to set it down.
You can comfortable hold steel at 120F and below.


These are all reference points that come in handy when judging temperature. Get a tempering colour chart.

Rick
 
Tai, you could answer that a lot more clearly than I, but I was talking about basically creating a nest in the coals for the muffle to rest in. Could you do the same thing, create a trough/nest for the muffle, and then suspend the tube in the trough? It might get you a little bit more heat onto the side walls of the muffle.

--nathan
 
Something I didn't know for years, but seems really foolproof on hardening the 1084 steels

Melting point of Sodium Chloride - Kosher table salt (has no iodine in it)

801 °C, 1074 K, 1474 °F


That's really a handy reference for heat treating
 
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12345678910 said:
That's really a handy reference for heat treating
Click to expand...

It is as long as you bring up the temperature very slowly. Otherwise the salt will heat faster and more evenly than the steel and you'll undershoot the temperature. Try it in conjunction with a magnet. I would be afraid that the salt would only be telling you the heat of the forge cavity. I ran into that problem training with Tempilstiks. There are ways around it, though.

Tai Goo said:
Good one Rick.

I do that sometimes, but don't usually have any problem with "hardness".
Click to expand...
Tai,
Somehow I knew you'd jump all over my hard thing....




Rick
 
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silver_pilate said:
Tai, you could answer that a lot more clearly than I, but I was talking about basically creating a nest in the coals for the muffle to rest in. Could you do the same thing, create a trough/nest for the muffle, and then suspend the tube in the trough? It might get you a little bit more heat onto the side walls of the muffle.

--nathan
Click to expand...

Well yeah, use an insulated ducks nest. Most charcoal forges already have that. I use a huge bed of wood ash when I do it that way, but I would still say "over" rather than "in" if you have the top covered. The sides need to be somewhat open so air can circulate freely, since they should be working mostly on draft rather than blast for HT.
 
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