quenching medium

[Noah Wagener]

If i do not know what the steel is, is it better to quench in oil or water? What are most modern files?

When using MAPP torches, do you just heat in the open or do you try and house the item somehow?

[george wilson]

For quenching old files,water should be o.k.. It should not be ice cold. Just room temperature,but NOT warm either,or it will not give full hardness. The quench needs to be large enough that it does not get appreciably warmer when a tool is quenched in it.

I get a lot more heat out of a torch by laying a layer of bricks down,then,putting a few up on edge to form a corner to lay your steel in. You can get something like a plane iron much hotter,and a larger area of it heated by doing this. Two MAPP gas torches are a lot better than one also. For larger jobs,a weed burner with a trailer gas bottle will give a great deal of heat. Use it out doors,for sure.

[Dimitrije Stamenkovic]

Generally it is better to use oil. Water will work, but it will cool the steel much quicker and will make it hard and brittle and large items might crack during the operation, while oil is more gentle.
Old-time blacksmiths used to have their own secret recipe. In my country there is a famous, very traditional scythe shop and the blacksmith there uses a liquid mixture of wax, vegetable oil, beaver and bear fat and something else to quench, and his scythes are top-notch tools, used by scything champions.
Blacksmiths that I know generally use kitchen-grade vegetable oil and it will work fine. If you want something modern and precise purchase special quenching oils or solutions, but I don't think you'll need that, they are designed for industrial use.

Modern files are generally made of high carbon, tool grade steel, the same used for drill bits (the ones for wood, not the HSS ones) and everything else, but they have a harder temper. I have heard that sometimes they are carburized, which is a heat treatment that adds more carbon to the surface, making it even harder but without making the body of the file brittle, but I'm not sure about that and it is not important if you are going to work on them. Files and rasps are the most convenient source of tool steel, when they are worn out.

If you are making something small it's okay to use a torch, but if you need to temper a larger item you'd better make a small furnace, which gives you a uniform heating and also helps with heat dispersion giving you a higher temperature. You can just lay some bricks and it will work.
This is a furnace made by a local hobbyist knife maker and it looks like a very nice design to me:

289083
289085

He put a tube inside a can, and between them he poured heat-resisting mortar with a hole for the flame. Using more than one can you can stack them and make the furnace as long as you wish. As you see he uses two cans with two simple blow lamps, with better torches you'd get even better results.

Using the furnace outdoors might be safer, but it is better to do it in a darker environment to see better the color of the bright steel, which is essential for a good temper.

[Winton Applegate]

Brick
I would be a CAREFUL of regular old bricks from out in the scrap yard etc.

They take on moisture.
Could explode ! ? ! ?

Fire brick for furnaces is a good idea. Reflects heat, doesn't blow up, are very light weight to move around, easy to cut or shape for special purposes.
Get at a brick yard or Jewelry supply store .

http://en.wikipedia.org/wiki/Fire_brick

As far as oil or water try both.
See which works the best.
Then make your project.

[Winton Applegate]

secret recipe

Dimitrije,

Nice post and photos !
When ever I hear "Old time crafts person recipe"
ha, ha, ha,
I immediately figure it is going to contain some kind of urine.
In this case beaver and bear.
Thanks for making me wrong.

ha, ha, ha,

[Daniel Sutton]

You should visit iforgeiron.com. They have a section on heat treating and many knowledgable smiths. http:// http://www.iforgeiron.com/topic/9030-intro-to-heat-treating/#entry88485 ( http://www.iforgeiron.com/topic/9030-intro-to-heat-treating/#entry88485).

[Noah Wagener]

Thank you.

Are concrete pavers dangerous too? How about stone?

[Daniel Sutton]

Concrete can be very dangerous. I highly suggest looking into a single brick forge setup. You really need fire brick or an equivalent to be safe. There are many things that can go wrong once you get a fire hot enough to heat treat steel. Also, try choosing an oil that won't ruin your oven when you temper the blade. After you quench the steel it will be very fragile and needs tempering. I've seen water quenched spring steel shatter like glass without tempering.

[george wilson]

LOOK: You MUST use the quenching medium the steel was designed for. There are water,oil,and air quenching steels. I wish people who do not understand this would not post incorrect information. Sorry,that is that way it is. FILES are WATER HARDENING,NOT OIL. I will warn you,files have a lot of carbon in them,and no matter how much you draw(temper) them,they will STILL be pretty brittle,and can snap off in your face if you try to make a wood turning chisel out of them. I had that happen way back in the 60's,before I had enough experience. I drew the chisel blue,and it still shattered,just missing my ear(and,razor sharp,too). A normal steel,like W1 or 01,would have been a spring at a blue temper(clock spring blue). And not at all brittle.

I have been using tool steels for almost 50 years by now,and was the master toolmaker in Williamsburg. I got seriously involved with tool steels in 1970,when I had to make tools for the musical instrument maker's shop I was putting together in the museum. In 1986,I became the master tool maker,and used it all the time. But,I was making tools at night since the early 70's,which led to getting begged into becoming the tool maker.( I'd had enough of dealing with the public by then,anyway).

If you quench water hardening steel in oil,it will not cool fast enough to properly harden. If you quench oil hardening steel in water,it will cool too fast,and can crack,or at least form a poor molecular structure.

Air hardening steel should be allowed to cool just in air. Still air is just fine. A fan is not needed. Again,if it cools too rapidly,as in water or oil,it can crack,maybe violently,and you could get searing hot shards in your face. I recommend that you stay away from air hardening steel. It has to be protected from the air while white hot,or it will decarb. You will not be able to get it hot enough anyway. Use 01. It is a very commonly used tool steel,and not as treacherous about cracking as water hardening steels.

Yes,concrete is dangerous. If it gets hot enough,it will violently release the water,which IS STILL IN THERE. That's why you see piles of collapsed concrete powder after a fire in a concrete building.The best thing to use are fire bricks,which are designed for the heat. They don't cost that much.

For an oil quench,you can use vegetable oil. We used automatic transmission fluid,which worked fine. We had 5 gallon quenches. A 1 gallon quench will be large enough for most home shop use. Our oil quench would catch fire A LITTLE(Not the actual quench,just the oil clinging to the hot part as it goes into the quench). We had 2 large exhaust fans above our quenches in the tool maker's shop to get rid of soot and smoke. If you don't have exhaust fans,do your hardening out side. Your wife might not like the soot on the walls!!

[Noah Wagener]

Also, try choosing an oil that won't ruin your oven when you temper the blade. After you quench the steel it will be very fragile and needs tempering.

I was thinking i would reheat with the torch for tempering to straw color. Should i be using the oven instead? I have read to temper immediately after hardening. Is there anything crucial to the timing? I'm thinking an oven would take a while to get the steel to 500 or whatever but maybe that is inconsequential.

George, should files be tempered at a pretty high temp to make them less brittle? Should they maybe hardened at a higher temp too? I am reading a tool book that has a miniscule section on heat treating. The author states to harden at cherry red and any hotter will cause loss of carbon. Maybe that is a good thing with files? I am just starting small with some marking knives and cutters for mortice gauges. The files were made within the last five years. Well, bought within that time anyways. They are still most surely water quenched? Also, i have seen you write that you should not make a bevel until after hardening and tempering as the thinner metal will warp. Do you mean make no bevel at all or just not take it down to an edge?

[Doug Hobkirk]

I'm clueless. (But I find the thread is fascinating.) I need help in why you are tempering.



Are you talking about taking a regular file and tempering it to harden the steel?

Is this already done by the manufacturer "never" or "sometimes" or "almost always"?


Or is this a special situation where a particular file lost its temper? (From overheating?)
Do these answers apply to chisels? Are you tempering them routinely? Also with a water quench?

[Jim Koepke]

If you quench water hardening steel in oil,it will not cool fast enough to properly harden. If you quench oil hardening steel in water,it will cool too fast,and can crack,or at least form a poor molecular structure.

First let me say my knowledge on this subject is nil.

My question is about the above and how it may relate to something I read someplace. It suggested that it was best to first try hardening in oil and if that didn't work try water.

Is that an acceptable/safe way to proceed with an unknown steel?

jtk

[Noah Wagener]

Doug, I want to soften (anneal) a useless file to make tools out of it and then re-harden and temper. Tempering is a softening of steel after it is hardened. I know that sounds odd. Apparantely hardening locks in a certain structure and it has too done in a state that would leave a blade too hard for most uses.

[David Weaver]

First let me say my knowledge on this subject is nil.

My question is about the above and how it may relate to something I read someplace. It suggested that it was best to first try hardening in oil and if that didn't work try water.

Is that an acceptable/safe way to proceed with an unknown steel?

jtk

Yes, though it's still better to know what you're using and use the right thing first to limit the number of times you heat it, but if you don't know what you have, that's a decent way to proceed.

It's better ,in general, for hobbyists to stick with oil hardening steel - specifically O1. It's just easier to work and in my experience, it warps less, and you can harden and temper it to 60 hardness without issue if you want, or somewhere in the 58-60 range to have a very nice iron or chisel.

Of course, if you're making tools out of old files, then you'll need to use water, but you don't have much to lose using beat files, though.

[george wilson]

Do not bevel at all before you harden the steel. It WILL warp across the width of the blade because there are 2 different amounts of surface area on either side of the plane or chisel.

A good,normal tempering temperature is 400º for cutting tools made from water,or oil hardening steels(or even air hardening steels. I make punches and dies that will cut 10,000 cycles before re grinding. I use A2 air hardening for them. You should stay with oil hardening for a few years,at least.) For a fully hardened file,750º is not too much,and the file will STILL be brittle.

It is best to temper IMMEDIATELY after the quench,while the steel is still so hot that you can barely hold it in your hand(130º). This will make a longer lasting cutting edge. Have your tempering method ready to go.

A torch is fine for tempering. Heat the blade on the end away from the cutting edge. The steel must be sanded clean so you can see the colors change. Let the heat creep up towards the edge. Heat very slowly. Move the torch back and forth across the WIDTH of the blade. Let the torch go completely off the edge,hesitate,and bring it back. Repeat. You must have patience above all. This is the secret to getting a good,long length of brown on your tool. For instance,you could have 2 or 3 inches of brown color instead of maybe 1 inch if you were patient enough about heating the blade.

You can use the oven,but kitchen ovens can be off by 75º. If you have an electric stove,you can try laying the blade on the burner,with the cutting end hanging off the burner. Try setting the burner to low settings. Patiently wait to see what color it makes the steel. If it heats the blade too fast,quench at once before the blade gets too hot. Then,try again on a lower setting. Or,just use the torch.

I often use a toaster oven,but with the LONG thermocouple of a high temperature thermometer stuck in it. I buy them from Brownells Gunsmithing Supply. I ruined one by accidentally touching a live wire in a toaster oven once,so be careful where you insert it. Toaster ovens are even used industrially by professional heat treaters. That's where I got the tip.

The toaster oven is really the best option. You can get the whole tool tempered evenly. I recommend you get one plus the DECENT thermometer(not an ordinary cooking thermometer). Get the Brownell's one. It is worth the investment. Not that expensive.

Files will be brittle no matter how hot you temper them. They have about as much carbon as a straight razor (1.25% carbon). I will warn you that this may be totally different on modern files as they try to cheapen everything. Files 100 years ago were much better sources of cheap steel than they might be today.

Files ARE also surface treated with cyanide(don't worry,it can't get out!). These days,the file might just be surface hardened,and mild steel inside. If you break the file,and it is hard clear through,it is o.k.. No telling about Asian stuff.

You need to completely grind off the teeth in any case. If you don't,your cutting edge will get serrated as it dulls,because that cyanide sinks in a little below the tooth depth. So,completely eliminate the teeth + a little extra.

If you are making a chisel to be used by hand,it is o.k.. Just do not go twisting it,levering chips out,and NEVER use a file for a wood lathe. VERY dangerous,as I have mentioned. I could have been badly injured in my face so easily. My chisel was 2" wide,and weighed enough to hit me hard,but missed me.

You can draw the file blue,and should,but,it will still be more brittle than it should be due to the high carbon content.

[Steve Voigt]

Hi George, I'm enjoying reading your thoughts on this topic. One question: I thought old files were 1095, which would make them (approximately) .95% carbon? I don't really know though. Maybe they used something closer to W-1?

Also, for the OP, one thing about the whole oil vs. water debate: The smaller the part, the less it matters. If you are quenching some big die made out of 1" plate, it will cool much faster in water, so if you use the wrong medium, you will have big problems. But for something small, like a little chisel or file, the differential in cooling time is much smaller. This is the main reason people can often get away with cooling water-hardening steel in oil. If it's water-hardening steel, it will not get as hard in oil, but for a small part it may get hard enough for whatever you're using it for.

[Daniel Sutton]

You can use either to reach the same end. Some people use their oven for tempering and have had negative spousal responses to tempering automotive lubricant quenched steels. There are many books and articles you can read that fill in all of the nuance of heat treating steels. If you ask around there may be a smith in your area that has the equipment and can walk you through the processes.

[Dimitrije Stamenkovic]

I understand the concepts of oil, water and air hardening, but you talk about a degree of precision I would apply to mechanics, not woodworking. I know a lot of people like to apply metalworking concepts to woodworking, but I don't think that is really necessary.

What today is called water hardening steel is the same steel that has been used for centuries and oil quenching works well enough with it. Oil doesn't harden steel as much as water but makes it hard enough to be used for a tool. Also it is safer than a not properly executed water quenching, which might harm a novice.
Anyway you won't lose the steel and you can quench again in water if the result doesn't reach your expectations.

If you can't draw the brittleness out of a file probably it's not a good file to make tools out of, but I have plenty of them that are not that hard and that can be turned into soft steel. Files are not all the same, they may have different degrees of hardness and have different purposes.
I expect that one is able to spot the difference before he tries to do something like this.
You should really consult somebody who knows about these things and that can show you in person instead of just looking for information on the Internet. Forums are not good for learning from nothing, but they are nice when used for confrontation and enhancement.

Master blacksmiths I know use vegetable oil to quench tools made with old files and rasps and they make the opposite of poor quality tools.
According to my experience their methods (like the bear fat quenching which makes you laugh) work better than any modern industrial process, like in the case of the scythes I talked about earlier, or very old hand planes and chisels.

[george wilson]

Doug: TEMPERING is done AFTER hardening in order to soften the hardened steel,and add toughness. Fully hardened steel is brittle,like glass. It will not hold a good edge,because the microscopic edge breaks off,making the tool seem dull.

Files are fully hardened. They have to be in order to file steel with them. They get away with being fully hardened because they have thousands of cutting edges(the teeth).


Like David(and I) have said,use 01 oil hardening steel. It is easily available,and is less treacherous about warping and cracking when quenched,than water hardening steel. Indeed,it is becoming more difficult to get different sizes of W1 water hardening steel. Manufacturers are making more sophisticated steels these days. 01 oil hardening is at the bottom of the heap of modern steels,really. It is still in common use,but a die made from it will not hold up as well as better steels. It is fine for wood working. Some dies cost hundreds of thousands of dollars,and must therefore last a long time. However,these more advanced steels are complicated to harden and temper with home shop equipment,must be protected from air,and are best left alone. I have the means to use it,but most do not. You have to have a range of heating temp within 25º accuracy,for example,to get the most out of them. I use an electric heat treating furnace,with an accurate thermocouple. I wrap A2 steel in stainless steel foil to exclude the air,but it is $115.00 a coil.

Dimitrije,you do not know me,but I am a professional. If you harden a tool made from water hardening steel IN OIL,and RE harden it because it did not get hard enough the first time,you should normalize it first. Best to just use the proper medium to begin with. The optimum molecular structure of steels is not so simple. and,we ARE talking about metal working,unless Noah is making his blade out of wood.:) Working with metals? Best to learn the right way to do it.

Steve,what you say is true,but there is no need to confuse Noah with too much information when he is just starting out. I'd rather keep it simple as possible.

[george wilson]

Jim,you asked how to tell the proper quench for unknown steel.

Yes,you can begin with an oil quench,then go to water if the oil does not give full hardness. However,there is a great deal of air hardening steel in use these days,and blindly quenching a piece of air hardening steel in oil OR water can cause the steel to pop apart into shrapnel while it is still VERY hot.

There are spark tests that can tell you different types of steel without taking chances by quenching unknown types of steel. I am sure you can Google spark testing charts and get an illustrated chart showing what the sparks of different tool steels look like. If not,there are several books out there that can give you good charts,some in color,that will greatly help in identifying steels.

[Pedro Reyes]

Noah, if I were you, instead of all the guessing, if you are making one or two blades, why not go to McMaster carr, get an O1 piece. You can get a 1/8" (plenty thick for most applications), tight tolerance precision ground at 2-1/2" inches wide, you can get 18" of this (enough for 3 planes I gather) for less than $30 bucks.

To me knowing what it is, not running the risk of getting frustrated or much less injured is well worth $30 bucks.

Just my 0.02.

If what you are doing is simply a knife which won't see much abuse, then I understand, the idea of "making" it from salvaged stuff also appeals to me.

/p

[george wilson]

01 does not come already hardened,Pedro (If that is what you mean. But,I agree with not using "mystery" steel,for sure,if that is your meaning.). Noah's best course is to follow the advice I have given him since I have made hundreds of tools.

The best price for 01 steel would be Victor Machinery Exchange in Brooklyn,N.Y.. I have done several thousand dollars of business with them. Or,ENCO is another lowest cost site. I've done plenty of business with them,too. I think McMaster Carr is too high priced. Plus,you can never get a catalog out of them. I HATE online catalogs myself.

But,you can Google their catalogs and compare prices. Enco has very often been having free shipping lately. They pursue a very vigorous sales campaign,and times are tough. You need to get on their mailing list to get their "flyer" catalogs. They will readily mail a master catalog,too. But,the flyers will have special offers like free shipping in them. The shipping can cost nearly as much as the metal!!

I wait for a free shipping offer from Enco,then order heavy 6 foot long bars of brass,like 1" in diameter. Those get heavy,and cost a lot to mail. That's the smart thing to do. I hate paying shipping on an 80# bar of brass. Sometimes there is a minimum dollar amount to be ordered. They have to make a dollar somehow! Sometimes the free shipping offer is worth buying more metal.

By the way,if you notice "pre hardened 4140",it is not very hard at all. I mill it and drill it quite easily. Do not think about buying it. It seems no harder than unhardened 01,being a lower carbon steel(.40%).

[Pedro Reyes]

01 does not come already hardened,Pedro (If that is what you mean. But,I agree with not using "mystery" steel,for sure,if that is your meaning.). Noah's best course is to follow the advice I have given him since I have made hundreds of tools.
...

George, I only meant for removing the mystery out of the equation, I realize it is annealed (thankfully) and must be hardened.

I'll check ENCO as well as the other place you recommended. EDIT: already did :) $16 and change vs $26 and change, not bad, thanks again. (this is for 1/8", 2.5" wide 18" long)

Pedro

[Daniel Sutton]

Enco has free shipping over $25 in may. The discount code is MAY25.

[george wilson]

This will be for English made 01,but there is absolutely nothing wrong with it. Starrett always costs more,but with the decline in reliability and quality control of Starrett tools in the past decade,I'd just as soon have the English metal anyway.

Yes,machinists call unidentified metal as "Mystery Metal". I have a good bit of mystery metal laying around here,but have been able to at least figure out how it needs to be hardened. I use it for some things,but nothing serious.

[Steve Voigt]

If you are trying to make a woodie plane iron, you want thicker than 1/8. 5/32 (at the thickest point) was typical of 18th c. irons; 3/16 is good for 19th c.-style irons.

[george wilson]

I WISH 18th. C.irons were thicker,but I had a HUGE amount of trouble getting the blacksmiths here in the museum to make them over 1/10" thick. We argued for hours. The irons they had seen in our collection were that thin. If I'd known the trouble they would make over this issue,VS the USEFULNESS of the planes,I'd have made the irons myself. The curator came up with the SILLY statement that he thought ALL planes chattered in the 18th. C.. How he came to that conclusion,who knows.

I could only have wished that the curator could be someone who actually did woodworking. It would have been helpful if the blacksmiths HAD to use those planes too.

My main concern was that the planes should be good and useful to the craftsmen. Not quibbling about making the irons a fraction thicker.

I secretly made some thicker irons of more advanced metal for the coopers. I felt sorry for them,having to plane hard white oak all the time. The tourists never saw down into the throats of those planes anyway. I just felt sorry for all the guys who had to contend with too thin irons.

They were usually stingy with metal in the 18th. C.,because the metal was all hand processed. Carbon steel was even more work,which is why tools were bitted instead of solid like they were later on.

[Larry Frank]

I find all of this kind of interesting and kind of weird. How can anyone recommend heat treatment for an unknown grade/chemistry of steel? The only way is to guess at what the steel grade is and what heat treatment is appropriate. The danger is that you may think that you have succeeded and then go to use the tool that you made and have it fracture and hurt someone.

As for spark testing, we used to do this a lot in the steel mill and only by very experienced people. Yes, you can kind of guess the carbon level but without actual training it all be a guess. It was so difficult for some of the grades of steel and not totally reliable that we went to portable spectroscopic equipment.

I agree with the posts that suggest that you buy a piece of steel that you know what it is and then proceed from that point.

[allen long]

Good evening everyone. I thought it might be worth mentioning that tempering doesn't actually "soften" the steel. Rather, it relieves or relaxes the internal stresses. When you apply high heat, you really get the molecules excited. We are talking slam dancing, gyrating, twister crazy excited. The girls on one side of the room and the boys on the other side of the room loose their shyness and mingle. When you throw freezing cold water or oil (in relative temperature terms), everyone in this crowd stops in exactly whatever position they were in - arms and legs in all sorts of crazy positions. While the crowd has now become very hard in this position, it is not very tough - easy to knock over and break apart. When you allow the molecules to relax and put their feet down and take on a fighting stance, the molecular crowd becomes tough.

[george wilson]

Increasing the tempering temperature does something suspiciously like softening it.:) Heat it above blue,till it's gray,and it is fully annealed,or softened. At blue,saw spring temper,you can readily file it,of course,which you cannot do much at all at a brown color. I guess it depends upon your semantics.

Larry,as I mentioned,I don't use mystery steel for anything critical. However,its chemistry can be determined fairly well(with experience) by spark testing. Then, by a series of hardening and tempering tests,which I have mentioned. I have made quite a few things like small steel plane BODIES from mystery steel. They don't have to hold an edge,of course. The blade does.

For important uses though,I agree that buying the correct steel for the job is the way to go.

There is a lab in town where I can get metals tested for $25.00 a pop. I also have sent samples off to the Bureau of Standards,when I was at the museum. I had bought quite a few feet of round steel rod which I was sure was tool steel. I found out it was .80 carbon steel from the Bureau.

[allen long]

George you are correct, Sir. And not just a matter of semantics. In my zeal to make a point I should have said, the reason you anneal something is to relax / relieve the molecular stresses to make it tough, not to soften the steel. I believe the metallurgical world is always looking for that magic alloy and process combination that will yield a steel that is as hard as possible while still being tough (not brittle). There is always a trade-off between absolute hardness and toughness. We have not even talked about grain structure for sharpness! George, as a professional, is O1 the best bet for the serious home practitioner? You mentioned a couple of sources for O1 steel, but have you noticed any significant difference in quality between ENCO for instance and your other sources?

Kind Regards . . . . ALlen

[Pedro Reyes]

...I should have said, the reason you anneal something is to relax / relieve the molecular stresses to make it tough, not to soften the steel. ...

You meant temper, not anneal, correct? anneal is beyond critical temperature (IIRC the terms) tempering is below. Speed of cooling is also an important difference. Just clarifying.

Pedro

[allen long]

Yeah, what you said . . .

Temper is the correct term .

I am not a metallurgist - my son is. That is what I get for trying to sound smarter than I am!

Many Kind Regards . . . Allen




You meant temper, not anneal, correct? anneal is beyond critical temperature (IIRC the terms) tempering is below. Speed of cooling is also an important difference. Just clarifying.

Pedro

[george wilson]

Everyone sells the same 01. They either offer English imported 01 or Starrett. Just hope they don't start selling Chinese made 01. That is happening in the industrial world. Machinists are ruining cutters when they run into a half melted ball bearing or other crap they leave in their metal. Their plywood is about the same too. Smashed soccer balls,pieces of fencing and other junk has been found in their plywood.

[Ryan Baker]

George, I find your comments about tempering in a toaster oven interesting (especially from someone with a proper tempering oven). My own experience with toaster oven tempering has been more problematic -- possibly due to my particular oven. I found that the heating coils produced local regions of much higher temperature within the oven -- i.e. there were inconsistent temperature gradients throughout the oven. Due to the size of the oven, some areas of the part are much closer to the heat coils, without enough space and/or diffusion to even out the temperature. I have taken parts out with clear color stripes across them right in line with the coils, and they got to much higher temperature than the average temp of the oven.

I usually prefer to temper with a torch. But for larger parts or ones where I want a very even temper, I have had better success using a full-size oven (maybe even convection!). A "real" thermometer does make a big difference though.

[george wilson]

I can't remember the book,as I left it at work when I retired in 2009. It was by a pro. heat treater. Odd name,Szumera,I think. CORRECTION: I just recalled the name: It is Jim Szumera. The book is "The Tool Steel Guide". I just ordered myself a new copy from Amazon for $21.85(or close). I am glad to have found this book again.A very useful and very informative book. I have other books,but this one is more concise and to the point. They used toaster ovens in professional heat treating shops. That's how I got turned on to it. A good thermometer is essential. You can look at something like a plane iron or knife blade,to see that the color is even all over. Move it around,or turn it end for end if needed. There is still skill and judgement involved.

It is a wonder how,back hundreds of years ago,they made beautifully fire blued sword blades,perfectly fire blued from end to end(these were fancy gentleman's swords I have seen). They did this in primitive brick ovens,and all was skill,no thermometer!!

They are VERY rare,but they also made hardened and tempered shotgun barrels in the 18th. C. that I am aware of. This was only on the highest grade guns,and was done to make the barrels more corrosion resistant. Now,I can tell you,evenly heat treating a LONG tube of very uneven thickness is a challenge. The thin end wants to get hot quicker that the breech. A VERY evenly controlled oven is necessary. I think it is a huge tribute to their skill that the old timers pulled that off. I have fire blued tapered pistol barrels in an oven myself(the brass mounted pistol I've posted here,for example). I can tell you,it is not easy to pull it off,even with a modern,pyrometer controlled electric furnace.

At work,where I had the money,I had 2 heat treating furnaces made for knife makers. They were 22"deep inside,electric. I have one at my home shop. We'd pre heat one of the furnaces to the tempering temp.,and use the other one for hardening. As soon as the part was quenched,and we could barely hold it for a few seconds,into the tempering furnace it went. That was an ideal setup. But,those furnaces are over $1,000.00,and I am lucky to have one. So,the toaster oven will do.

For smaller parts,I use the torch. They are easier to evenly heat with a torch.

[David Weaver]

I don't know how those guys knew what temperature they were tempering gentleman's swords, but I've seen harder temper japanese knife makers temper knives by heating them at the top of a forge and taking them out of the forge every so often and dropping water droplets on the blades to judge how hot they are by the action of the water droplets.

I use a kitchen oven to temper anything that I make that's not tiny, but I have a thermometer in it and I let whatever is in the oven temper for an hour. If the oven isn't preheated very long, I've noticed that on mine ( a ge convection oven) that the front is much cooler than the back, except for where the air circulates first in the oven. A good toaster oven would probably have a much more even heat (except maybe right at the window) and be up to temperature much faster.

[Roderick Gentry]

I find all of this kind of interesting and kind of weird. How can anyone recommend heat treatment for an unknown grade/chemistry of steel? The only way is to guess at what the steel grade is and what heat treatment is appropriate. The danger is that you may think that you have succeeded and then go to use the tool that you made and have it fracture and hurt someone.

The file example aside, there is virtually no risk of someone getting hurt. It probably helps not to pry the heck out of a mortise chisel if you can't tie a shoelace, and whipped the chisel up yourself. I normally just HT the end of planes and chisels. I am never going to get through an inch to 2 inches of material in several hundred planes and chisels. Even the old dudes who worked hard, died with shops full of nicely resalable tools. So if you don't even harden the material all the way (pretty typical approach for one reason or another) It can't snap.

At one point I made up a batch of plane blades and they turned out badly. The first I knew of it was that the edge hit a very hard knot and bent! I had been using the thing for about a year, and never noticed unusual wear or differences in sharpening (O1 blade in this case, but a goof is a goof). It was an interesting experience to see how effective even a goofed tool was, when it was not in one's brain that it had any problem. Some in the batch had skidded a file, so it seems as though they were coming out OK.

Even with the lathe tool example, in what universe today are people making thin sectioned scrapers, overhanging them a mile, then making heavy cuts. I just don't see how a small tool like that gets all over the shop if it was handled in any kind of competent manner. It won't be worth the trouble though, as the cost in abrasives to get it ground down, alone, is not worth the savings.

In the old days they used scrap approach to forging climbing gear (old meaning 1960s). Now there you might want to be sure you were getting axles or something.

As for spark testing, we used to do this a lot in the steel mill and only by very experienced people. Yes, you can kind of guess the carbon level but without actual training it all be a guess. It was so difficult for some of the grades of steel and not totally reliable that we went to portable spectroscopic equipment.

I agree with the posts that suggest that you buy a piece of steel that you know what it is and then proceed from that point.[/QUOTE]

[Gary Muto]

One way to improve the temperature profile in an oven (without a fan) is to make the surfaces as clean as possible. A lot of times the top of the oven goes unnoticed.