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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 12-09-2014, 01:47 PM
mukluk mukluk is offline
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differential heat treating for the perplexed

I've been reading in preparation for a first knife. I should have stopped and tried one while I knew what to do, but the more I look the more opinions there are and it's paralyzing and frustrating.

I'm coming to this from blacksmithing. I was all set to temper my blade by applying heat to the spine ( by torch or by setting it on a hot bar of steel), I was going to go by color and run the colors up to the cutting edge. Then I looked on the knife maker's sites and everyone seems to be using multiple cycles in an oven.

I understand that there are problems with color being subjective, and that the color line might not meet the edge evenly. But I don't understand the oven...I really thought it was highly desirable to have a hard edge on a tool and a tough 'body' behind it, and I don't see how this is achievable with an even heat in an oven???

I really want to get making stuff, and not spend hours agonizing over different theories and (perhaps?) slight differences in performance. I'm leaning to using the old traditional methods and heat treating by running color from the back. For what it's worth my interests are in primitive knives, bush knives, historical knives of fur trade/old west / middle ages, etc, or more fantastical blades inspired by those traditions. I'm a farrier and I have a lot of worn rasps piling up, and I'll be using them against all the admonitions to only work with known steel...

Any thoughts welcome...if you think i'm badly off on the wrong track or not...right now i feel like i've got to start somewhere, but if i need to get a thrift store toaster oven to do a better job i will..
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  #2  
Old 12-09-2014, 04:20 PM
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Ray Rogers Ray Rogers is offline
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We don't actually tell everyone not to use files, what we actually do is suggest that beginner's not use unknown steel. Later, when you know what you're doing you can use whatever you like but, as you have been discovering, there is a lot of apparently conflicting advice concerning heat treating . I say apparently because it is a certainty that all those sources you are reading are not using the same steel (whether a known steel or not) and different steels must be handled different ways.

For general blacksmithing or farrier work all steel looks pretty much the same but not so for knife making. Only certain types of steel will make a really good knife using the methods you have chosen and only then when the heat treatment is done well. If all you care about is that the knife cuts stuff and holds up to average use then you can use almost any steel and heat treat it pretty loosely. That's not what we aim for here and since you are here I'm thinking that's not what you want either.

BTW, furnaces are used when available because they remove the guess work concerning temperatures. Precise control is how you get the most out of your blade steel. Lots of guys learn that control using their forges but its just a lot easier with a furnace. And, even with a furnace there are several ways to have a hard edge and a soft back if that's what you want so you don't have to give up anything to use a furnace and, generally, you can expect to gain.

So, since you want to "get to making stuff" then let's discuss the quickest way to do that. You are a blacksmith so I assume you have some kind of forge and you know how to control the temperature in it. Use the forge to heat your blade (whatever it may be made from) and then quench the entire blade in warm oil. After that, immediately temper the blade.

That is the basic steps and they will work with any unalloyed steel that has enough carbon to be blade worthy. For the moment, forget about a hard edge and a soft back - you really only need that if you are making a large knife intended for heavy chopping, if then. Properly heat treated, any blade steel is tougher than all get out and can probably get along just fine without the soft back.

For your first knife, you should be making a 4" hunter or similar sized knife, not a Bowie, not a big chopper. Whatever steps you end up using concerning shaping and heat treating your blades are going to be easier and faster on a smaller blade than a big one. Right now, you need easy and fast so that you can make several blades one after the other and figure out what you should be doing. Don't think fancy, don't think big until you master your heat treating.

So, use a rasp if you wish, make sure it is not a case hardened rasp - it must be hardened all the way through. Heat it, beat it, and shape it as you wish. Get yourself a good magnet and attach a handle of some kind so your hand isn't too close to the hot metal when you need the magnet.

Slowly heat the steel and test every 30 seconds or so once the steel starts showing color. The idea is to find the point at which the steel stops being attracted to the magnet - exactly that point, not 300 degrees later. Do not leave the magnet in contact with the steel for more than a second or two, the heat will ruin it.

It is also important to catch that non-mag point while the temp is rising. It is not good enough to over heat and then try to catch it on the way down. Once you have found that temperature hold the steel in the heat about another 15 seconds and then quench in warm oil.

The oil should be about 100 F and it should not be used motor oil. You can use hydraulic fluid, or mineral oil, canola oil, ATF, peanut oil but not motor oil.

After the blade cools in the oil to where it is merely warm to the touch wipe off the oil and temper the blade immediately. That toaster oven is a good way to do that. Cook the blade at 425F for one hour, cool it to room temp, and temper it again. You're done.

Now clean up the blade, put a simple handle on it, sharpen it, and test it to destruction. Cut things, carve wood, slice cardboard, stab stumps and twist the blade out, torture it within the bounds of anything you can imagine might ever be done to it in real life. Then put on some eye protection, put a pipe over the handle with the blade in a vise and break it, look at the grain. If the testing showed chipping or the blade cracked its too hard. If it bent and stayed bent its too soft so adjust your tempering temperature and make a new blade. If nothing you do makes a blade that can pass these simple tests the either your heat treat is still wrong or the steel you're using will not harden sufficiently.

That's the basics. Do that first and get to where its easy, then if you prefer to work by color you have a chance to know what the correct colors are for whatever steel you are using.

PS

The heat treat process can be more sophisticated than this, for instance, I left out normalizing and possibly annealing on purpose as they probably won't be needed if you are using an unalloyed (or not significantly alloyed) steel. What I described are the minimum steps. Learn to do these steps correctly, then worry about adding extra steps like differential treating on top of these steps if you wish....


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Last edited by Ray Rogers; 12-09-2014 at 06:34 PM.
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  #3  
Old 12-09-2014, 05:18 PM
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ricky_arthur ricky_arthur is offline
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Once Ray has said it, there isn't much to add. But I'll just say that tempering in an oven is FAR easier and more controllable than a torch along the spine. A properly heat treated blade followed by an appropriate temper will give you all the toughness and hardness you will need on a 3-5 inch blade.
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  #4  
Old 12-09-2014, 05:24 PM
jmccustomknives jmccustomknives is offline
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Some rasp are great, others are case hardened and as such aren't suitable for anything but the scrap pile (or rasp asp, lol). As far as the differential thing goes, learn the proper heat treat first. A small knife benefits very little from this style of heat treat. You can use Rays method, it will serve you well. If you are willing to ruin a few try out the rasp.
I will tell you, all the rasp I have acquired that were made in Spain were case hardened. The Heller seemed the best. You can test them by heating the tang to non magnetic then quenching them in water. Put them in a vice and try to break the tang. If it snaps clean it should be usable, if it bends throw it in the junk pile.
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  #5  
Old 12-09-2014, 08:57 PM
mukluk mukluk is offline
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Thank you so much for the replies! Ray, especially, for that detailed, concise response, and for giving me a place to start from! I really appreciate it.
I will test for case hardening. There are heller's in the pile, as well as save-edge and some bellota. I like sticking with one brand so if I find something that will make a decent knife I can keep myself supplied with a consistent steel and learn how to work with it.
As far as working the steel, if I anneal first and then forge will the forging have an effect on the grain quality in the final, tempered blade? I will keep it cool enough that I'm not burning off the carbon, and hot enough to avoid cold shunts ( I ask because I'd sooner spend time at the forge than at the grinder, but I don't want to overwork it..)
Any quick thoughts on getting the quench right? I think I will use canola oil for now. Blade down and parallel to the surface of the oil, and jiggle it a bit?
Won't bother you guys with anything else until I've gotten out into the shop and done some experimenting...differential heat treating someday if I try to make some tomahawks or big blades...
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  #6  
Old 12-09-2014, 10:11 PM
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after you finish forge work, heat to just above non magnetic, then cool till color returns to normal, repeat at magnetic, then once more just below magnetic. On the last one, I turn off the forge when the blade hits the color I want and leave the blade in it, then let it cool slowly with the forge, the bricks retain enough heat to let it cool slowly enough that it is soft enough to drill or file, etc. Those 3 normalizing cycles should give you a nice grain structure and relive any stress from forging.

On the quench sounds like you got a bead on it, just follow Rays advice and do like you said.

One more thing, ask all the questions you want, this place is full of lookers and short on posters, so ask away and be sure to post pics of your progress.
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  #7  
Old 12-09-2014, 10:44 PM
Doug Lester Doug Lester is offline
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Use old files and rasps if you must but a known steel is better. The reason is that not all mystery metal is made equally. As Ray said, some files and rasps are only case hardened. Others may not be made of the same steel so once you get the heat treating routine worked out for one piece you will have to start over with a new piece.

I would suggest that you start out with something like 1080 or 1084 or even 5160 or 80CrV2. The last two are low alloy steels that are still a lot more forgiving than something like O-1 or 52100. Even the 1080 and 1084 that you find these days tend to be low alloy steels meaning that they are more than iron, carbon, and manganese with a little aluminum to deoxidize the steel and counter grain growth.

As Ray said the only blades that need to be differentially hardened are large choppers and swords. There are a lot of people who are doing differential hardening so as to display a hamon. They look nice but they don't really do anything. The only knife that differential hardening is a must for is the ABS test blades.

When it comes down to heat control for the various forms of heat treating there is no such thing as too much heat control. Even the simpler more forgiving alloys will turn out better with a regulated austinizing oven and a regulated tempering oven or high temperature molten salt pots. It's important that you match your steel to the equipment that you have. If all you have to austinize the steel in is your forge then stick with simple steels. That's not to say that you absolutely cannot use a forge to heat treat something like 52100 it's just that it's doubtful that you can do it reliably. Actually this leads to another problem with used files and rasps. Many of them are made from high carbon steels, as in 1%+ that needs good temperature control to avoid retained austinite.

Doug


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Last edited by Doug Lester; 12-10-2014 at 12:12 PM. Reason: changed annealing oven to austinizing oven
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  #8  
Old 12-10-2014, 05:35 AM
jmccustomknives jmccustomknives is offline
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To what will you gain by forging a rasp? There are a couple of things working against you. First, they are thin leaving little mass to work with. The teeth are cut deep, these will push down into the steel further thinning the usable material. Most will do stock removal as such on rasp.
If you want to learn how to forge get known materials, if like me you are cheap, acquire a modern truck leaf spring (usually some version of 5160). There may be defects in springs, but there is a lot of material to learn with and that alloy is very forgiving for newbs and makes a good knife.
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Old 12-10-2014, 07:08 AM
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Not much left to say. Well done Ray.
Since you have the rasps in hand and want to use them then use them. Already being familiar with fire and hammer, you have a step up on most beginning bladesmiths (just remember it's not a horseshoe).

Only a few things to add:
Grind the teeth off in the areas close to the intended cutting edge and tip so that you don't force forge stress cracks down into these areas.
Place an extra oven T-meter in the toaster oven you plan to use for tempering and test the oven's settings - they are usually pretty far off. Set you oven where there is no cross draft to pull heat out the glass front. Make sure the knife blade will fit easily into the oven before you start the heattreating process. And, preheat the tempering oven so it's up to temp before you go through with the hardnening quench - it needs to be ready.

From experience I have found that Bellota's tend to be a bit lower in carbon content than the Heller's and Safe Edge's. Also modern car and truck springs are just as much a crap shoot as the rasp. You will have to test them just like you would the rasp to achieve consistency.

As stated more than once above, it is very hard to beat learning with known steels like 1084 or 5160- it takes a lot of guesswork out of the equation and greatly reduces the learning curve while you get the basics engrained.


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  #10  
Old 12-10-2014, 08:56 AM
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Ray Rogers Ray Rogers is offline
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QUOTE: As far as working the steel, if I anneal first and then forge will the forging have an effect on the grain quality in the final, tempered blade?

Mukluk,

There are several ways to look at that question. First, if you are forging a blade to shape then it isn't really necessary to anneal the steel first since the forging heat is enough to make it as soft as required to shape the steel. Annealing is needed when you need the steel to be soft for drilling or sawing.

Second, yes, forging can have an effect on the grain quality of the finished blade - BUT maybe not the effect you're thing of. The grain can be large and coarse and the blade weak because you forged too hot and didn't normalize or because you let the blade go too far beyond non-mag before you quenched. That's how forging could negatively affect the grain structure.

But if you are asking if forging in and of itself will/could result in a better grain structure than shaping the blade by stock removal then the answer is simply 'no'. The simple act of forging the blade does not create a better grain structure in a blade that any other method of shaping a blade, it is the heat treatment that determines the grain structure. That is why we are harping on control, control, control.

That isn't to say that a Master Smith that really understands metallurgy like Ed Caffrey or a guy like Kevin Cashen can't forge a slightly better performing blade than an equally skilled maker might make by stock removal but, if they do, it will be because they were able to more precisely match the heat treat to the steel they were using than any innate characteristic of the forging itself. In point of fact, I don't think either of those two luminaries actually heat treat their forged blades in an actual forge when they really want to get their best results (I believe Caffrey uses a Paragon and Cashen uses salt pots). In short, any skilled maker using stock removal and an electric furnace has the same possibilities for making a high performance blade as at least 98% of the guys who forge their blades.....


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  #11  
Old 12-10-2014, 12:57 PM
mukluk mukluk is offline
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Thank you all again for the tips and the encouragement.

Please know that I'm not suggesting that forging is superior to stock removal, or that one heat treatment is better than another...I'm just trying to understand the benefits and limitations of the techniques so that I can make the best blade I can with the tools and skills that I have available. I enjoy working at the anvil and want to develop those skills anyway, as they will crossover and help me improve my general blacksmithing and horseshoeing. If I progress into more full-time shoeing I'll have a constant supply of good-sized uniform rasp steel, so if I can find a way to make some reasonable quality blades from it I'll be happy. (i also like the aesthetics of blades that aren't too perfect, where you can see some traces of the hammer and the process...but that's just me )

I had thought that annealing would even the piece out and help me introduce less stress in the piece while forging. Thanks for the info on reducing stresses post forging, and the tip on grinding off the teeth in the edge area. I'll be sure to come back and post with my experiments to get some feedback. It's nice to have community. Thanks.

Last edited by mukluk; 12-10-2014 at 01:07 PM.
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  #12  
Old 12-10-2014, 01:27 PM
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Ray Rogers Ray Rogers is offline
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QUOTE: It's nice to have community.

Yes, it is. We extend the community a little further by having a Chat Room every Sunday night from 5 pm - 8 pm Pacific time. The Chat Room is aimed specifically at new knife makers so you would be very welcome to drop in. No special equipment or software required, just your computer and some minimal typing ability. There is a Sticky thread at the top of the forum with the details if you're interested....


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Old 12-11-2014, 07:39 AM
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I think Ray hit on it pretty solid.
You will be introducing so many thermal cycles to the steel as you forge that final normalizing steps are the ones that will have the final say on the condition of the steel.
Yes you can damage steel while you forge it - hitting too cold and introducing stress cracks, getting it too hot and burning out carbon, etc. Different steels have different thresholds of tolerance. You will have to learn these and working with mystery steels just makes this part trial and error harder - big part of the reasoning to use a known steel to learn.

The final thermal cyclings you put the steel through will be a major part of the quality of your end results. The better you control this the better the blade will be. The other deciding factor will be blade and edge geometry which is end purposed use driven. Get both of these right and you have a good knife, wrong and you have a knife-like object that won't even do well as a screwdriver.

Superior blades are made by good knifemakers that adhere to good practices. The steel is steel, whether ground or forged, and awaits good sound practices to bring out the properties that will make it a good knife.

It sounds like you are determined to use the rasps, this I understand. Make it easiest on yourself by sticking to only one brand until you feel you have confidently reached the point where you are getting the best you can from the steel consistently. Then try the other brands and compare results.


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