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I Forge Iron

Heat Treating in a propane forge.

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Up until today I've been heat treating knife blanks in a simple charcoal forge.
It's not easy to keep the temperature steady and even harder to keep the tip of the blade at the same temp as the rest of the blade.
One trick is to place a piece of steel tubing inside the forge and place the knife blank into that to get a more even temp,
but even this doesn't seem to help much since the tip always seems to get way to hot.
So, I made a propane forge from a can lined with 2 inches of ceramic fibre blanket treated with waterglass and a thin layer of refractory.
The burner is just the burner that came with my propane tank and the 2 bar adjustable pressure regulator.
Rumour has it that its hard to keep a knife blank steady at the desired temp inside a propane forge.
Today I tested with a piece of steel tubing inside the forge.
After ten minutes the steel tubing was glowing along its full length with a color indicating about 800 deg.C (1472F).
Then I inserted the knife blank (1095) and adjusted the gas flow till the knife got to non-magnetic and then some, and then I let it soak for five minutes.
The blade was at a very even temp along its entire length including the very tip.
Quenched in oil and tested with a file. File skated across the edge and then I broke off the tip and examined the grain structure.
The knife blank was glass hard and the grain structure was very even and fine which indicates the temp was high enough to harden the steel
but not so high as to cause grain growth.
So, yes,-it's seems to be possible to control the temp in a propane forge within reasonable limits.


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Yes, that's one way of solving the problem, but I have a small bunch of 1095 equivalent steel and it likes to soak for some time at temp
so the steel tubing method allows the knife blank to lay still in the forge without heating up unevenly.
I do admire japanese sword smiths that manage to heat the whole length of a sword to an even temp in a charcoal forge.
-I'm not quite there yet . . . if ever.

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I don't think heat treating outside of a computer controlled electric oven, is a very smart idea; that said, some heat treating jobs are simpler than others.

So, how to give the best shot at a satisfactory job from a gas forge? The keys, would be even internal temperatures and really good control in lower temperature ranges. Ribbon burners are going to provide both factors better than any other kind of gas burner. Since this work is done at lower temperatures, a hand held pyrometer should work okay for judging forge heat.

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Or you can buy "heat stops / blocks," at a welding supply. There are different kinds some just copper "blocks" you can clamp to the project to prevent heat from getting past. 

A wet rag, straw, etc. works well some folks use a watering can with a single spout to control the heat. You see the later most often when twisting bar.

Frosty The Lucky.

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  • 4 months later...
On 4/20/2023 at 3:33 PM, Mikey98118 said:

I don't think heat treating outside of a computer controlled electric oven, is a very smart idea; that said, some heat treating jobs are simpler than others.

I think there's some nuance to this. There are certain things that are very easy to do in the open air in minutes that take a long time in an oven, but I'm speaking as a maker and not as a buyer. I've also snapped a lot of samples and had some tested by larrin T (one matched furnace results, one set (26c3) was better - with individuals in each type heat treated separately, and not surprisingly, some other alloys that I never spent much time working up didn't come out well - imagine if you ran the furnace cycle for high hardness 52100 on 1084 and 1095, and you can get an idea of what I mean -good for 52100, but overhard and brittle 1084 and 1095 would result). 

I think there's no commercial value to any of what I'm talking about, though, which also negates too much discussion of it, which is fine. Nothing new, no magic, just trying to get an idea of how someone did some of these things 175 years ago with a little less control because some of the best edge stability I've ever seen is from tools made in England in the mid/late 1800s. Thus the hobby. 

I make tools as an amateur but generally only sell them to professional users.

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Over forty years back, I was in a wood carving class, that had to make our own hook knives as one of the assignments. We were to get the blades as close to finished as possible, and then send them out for heat treating in the college's fully automated electric heat treating oven. Most of the blades came back just fine, but a few were worthless. That was my first clue that the best industrial processes, may not be so hot.

Thank you for a mirror view of one of my own prejudices. It was the short comings of heat treating in 'the best possible' conditions that has given me pause for use of any "lessor" method; there was nothing lacking in that lesson, but there was everything wrong with my conclusions :rolleyes:

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I've used a lot of commercially heat treated stuff, but only have exposure to consistency on the hand and eye side (do have a metallurgical scope, a hardness tester, and thermocouples, though). I have some lack of trust, I guess, on the more plain steel side of things but am personally wary of other people who do sort of hand-eye heat treatment unless they have some data. I don't quite have the trust that a commercial shop would get my chisels heat treated the way I want them (posted elsewhere in this forum - and also straight at the same time as I don't leave much margin for post HT grinding and adjustment).... 

I'd trust a good heat treatment place to make a million A2 blades almost identical, though. I could be totally wrong about how things were done in the old days, too - I just assume it took someone who has a lot of repetition with personal judgement in 1850, doing things commercial heat treaters won't touch now (really warpy steel that makes divine chisels and scissors and razors, etc) - they could very well have had highly controlled process that was just controlled in a different way to take the maker's judgement out. 

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I'm an old man these days (77) The old west was during my granddad's time. I remember seeing photos of ordinary people from those days, looking like they were all trying to scare Jesse James, and confident that they could get the job done.

I grew up working in ornamental iron shops, with lots of guys from my grandfathers generation, still around; they were all hard cases. So, when I consider how things used to be done, its through the lens of that experience. I can testify that "the right way" of doing everything in a shop was considered far more solid than a library of book knowledge; including by most bosses.

The biggest problem with "progress" is the sloppy discarding of old methods, when  new ways offer bigger profits. Once the old guys die off, so does most of what they knew:P

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The reason the old timers were so good at judging things by eye is three (maybe more) fold. first there just wasn't instrumentation more reliable than trained human senses, Secondly (maybe should be #1) they worked with much fewer alloys, a touch of vanadium, manganese, molybdnum and chrome, was considered alloy steel and it wasn't so common till after WWII, Today those are considered plain steel.  Or thirdly, they learned from hard cases that made them do it over till they got it right and they only got paid for what they got right. 

I'm afraid the old timers are passing if not away then out of common practice because instrumentation and controls have become more accurate and reliable than the trained eye. If you go to the steel store to get some "MILD" steel, it's a special order and expensive so what passes most of the time is A36, structural steel or what Dad would've called medium alloy steel.  

When you say "profit" it sounds like you're talking about money but profit isn't so one dimensional. Profit simply means your return on investment is great enough to pursue the practice. One of the best examples of pure profit driven enterprise are the Kalahari bushmen. To say it'd dry country is understatement to the point of silly it's probably the driest inhabited place on earth. One of the only reliable water sources is a particular plant's root. It's easily pulled, a slit and squeeze produces a few tablespoons full of water, then it's returned to the ground to grow for another drink sometime in the future.

As the Bushmen travel they harvest water as they go however if the (call it water plant) is more than 3 steps out of the way they pass it because they will expend too much water to make it  profitable to stop, pull slit drink and replace it. Even if the whole process takes about a minute.

It's uneconomical, unprofitable. 

Most old methods being replaced are uneconomical and being uneconomical in a competitive world is the way to "extinction." Humans evolved competing for everything with animals and conditions where we were not very competitive. We could think and have thumbs and invented tricks and tools to make us competitive. It's worked for us for a couple million years why on earth would we stop now?

Heck, most of the new techniques and tools that make the old ways obsolete were invented BY the old timers.

While I admire and wasn't a bad hand at judging temp by eye I'd have a ramping kiln, precision controlled furnace and use modern alloys if I were making cutting tools today. Did you know almost every pop up toaster has a sensor eye that can judge the color of your toast to a fine degree? Seriously reliably produce barely tan for little sis, light to medium for you and Mom and dark brown for uncle Fester. Put one in a set position in a dim container, heat the blade from the spine or shank, when the edge tempers to the desired color it gets dropped into cool water to stop the temper running.

Does a company mass produce differentially tempered blades? I don't know of any, why with modern alloys that are not only cut steel hard but very impact and work hardening resistant?

Frosty The Lucky.

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I think you can get some heat treatment places to do differential heat treating, but I have short arms and some regard for what I'm doing because I think it would be hard to communicate if you're not doing something they've done before. 

For example, on the paring chisels I showed, if I said I need 63/64 for the first four inches and then if things fall off a little, it's OK. by the time you get to the shoulder, spring temper or less is fine, and the tang needs to be very partially hardened so that it's stiff, but it needs to be below spring, and behind the bolster nearly unhardened is OK. 

150 years ago for the actual process of making that would've just been routine. 

I'd have a furnace if I were making knives for sale only to avoid arguments - I get them already from amateurs asking if I will make them chisels, and I think they get confused when I say I am an amateur, at least in spirit, and I will not sell to amateurs but would be happy to help them find what they're looking for. They often want A2 or something else and would like to ponder if I've ever made a chisel out of 10V (I've used a plane iron in it - it's suitable for turning tools, but not good for chisels and plane blades). But if you are making knives to a whole bunch of people you don't know and can tell them you used a computer controlled electric furnace - the questions are off. I tell people who want to trade something (that's what gets me out of the chair - someone who has something I'd like and they want something unusual made in return, like seaton chest style chisels) that I work by hand and eye, and it's not comforting for some people to hear that. I've never had a pro who wants to trade bothered by that, but amateurs are very unsettled if I don't tell them a steel they've heard of before (none of them know 26c3, and they are sure that 1095 is only used in handsaw plates. W1 is a foreign concept - "do you mean O1?" and they're afraid of what they'll get from hand/eye heat treatment. 

So, here's a good example of getting really detached. There are some boutique tool companies with more than 100 employees, but those companies sometimes run into a bottleneck because despite using fairly common stable steels, they still will not do their own heat treatment. they need something that makes business sense. On the axe side, it seems like most things are 5160 or 4140 or something all the way around. And too much paint to tell if there's differential hardening. Some of the swedish axes are higher carbon, but the videos I've seen of them don't ring a bell with someone dipping only the bit end into oil. 

The woodworking world suffers from the same thing, even with one of the moderately educated writers constantly telling people that "O1 steel is just plain old carbon steel that's been around for hundreds of years" and the sentiment is that A2 is perhaps something that showed up in the 90s simply because that's when it first showed up in woodworking tools. O1 is, of course, highly alloyed compared to 1084 or 1095 or even W1. 

Process, machinery and changes in alloy are in some cases part of the age old battle that will go on forever -if you can change process to trade skilled labor for semi skilled or unskilled and maybe increased production at the same time, that will win. I'm agnostic on the whole thing - most of the time, I need the $30 version of something and not the $200 version of something. this dynamic of refining things so that less human intervention is involved increases the standard of living for most, just not the skilled guy who gets bumped out. I'm agonistic because sometimes the hand made stuff is nice, and sometimes it's actually better (1875 chisels are sometimes better than anything available now, but can't be made without the same skill set so they will not be made again), but it's also the case when you look at disposable income charts from 1900 vs. now, you realize that the average lower middle to upper middle class person didn't have many pennies left over for things like anvils and hobbies!


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