How to harden steel...?

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Hello people,

I recently bought a set of old Marples paring/pattern maker's

gouges which look very nice, but do not hold a sharp edge. I also

have some Pfeil gouges which are soft compared to other tools with

better steel.

I have read that some people harden their blades themselves, but I

don't know how to do this. Can anyone tell me a good way of

hardening my tool blades?

Thank you.

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I read from book if you melt iron (in high temperature) in liquid form and mix it with

carbon, then cool it rapidly (like drop it in water) it will become steel. Carbon+ cooling=steel.

(hard). If you let it cool slowly it become soft.

So try it heat your old tools and drop it in water to see if it helps. ( I've never tried it myself)

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This is too difficult to explain. You must get a book on the subject--there are lots of them out there. You can even search on Google and find out what you need. Basically, you heat the steel to cherry red color and then plunge it into water, brine or oil, depending upon the steel. Now the steel is too hard and you need to slowly reheat it to reduce the hardness--this is the tricky part. This is useful skill to develop and is easiest done with small tools or if you want to harden the tip of a larger tool.

The tools you need to harden (or reharden) are too large for heating with a propane torch if you want to do the entire tool. There are two ways to go in this instance: find a tool and die maker that has a furnace and get him to harden and anneal them for you or find a local blacksmith who can use his large furnace (heated by charcoal or hard coal) to do the same thing.

Most of my Pfiel tools were too soft--I sold them on ebay. I could have rehardened them but decided to make some money on them and then get better tools from such vendors as Two Cherries, etc. I hope you did not purchase my old Pfeil tools.

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Marples was (and is) an excellent Sheffield forge and I have found their tools hold edges really well.

Either yours have been messed with by someone re-heating and quenching in an uncontrolled environment or they are not genuine.


Steel is rather more sophisticated than Yuen has implied and there are many grades, alloys, heat treatments, forming processes and surface treatments. Ask an engineer or metalurgist if you have a few spare days....

Cooking and dunking will only make matters worse.

If you must :-




"To harden and temper a cold chisel by this method, you heat the tool to the proper hardening temperature and then quench the cutting end only. Bob the chisel up and down in the bath, always keeping the cutting edge below the surface. This method air-cools the head while rapidly quenching the cutting edge. The result is a tough head, fully hardened cutting edge, and a properly blended structure.

When the cutting end has cooled, remove the chisel from the bath and quickly polish the cutting end with a buff stick (emery). Watch the polished surface, as the heat from the opposite end feeds back into the quenched end. As the temperature of the hardened end increases, oxide colors appear. These oxide colors progress from pale yellow, to a straw color, and end in blue colors. As soon as the correct shade of blue appears, quench the entire chisel to prevent further softening of the cutting edge."

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While it's difficult to get tools up to temp with a torch, it's not impossible. You just need to tap all your friends for their torches. :-) I hardened my largest gouges with three torches, simultaneously, which did succeed in getting the temperature up where they needed to be.

The best way to temper is in an oven, which does just barely reach tempering temperatures--as Mike says, do your research and you'll find a lot about the temperatures you need. If you use a torch, you have to go extremely slowly, heating the base of the tool. Slowly. SLOWLY. Because what happens if you don't watch out is that suddenly you get the color that indicates where you're where you want to be will form where you're aiming the torch, and then it quickly starts marching out towards the tip, but quickly it passes, the base of the tool reaches a higher temperature, and then you watch the too-high-temperature color move out to the tip of the tool. . . in, say, one or two seconds, softening it too much, and then you have to start all over again.

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I have two 1 inch wide chisels made by Marples that are too soft--the edge will fold back on them. So even Marples cannot always be depended upon. All it takes is for the heat treatment guy to be off sick or the equipment to be broke that day, and the tools in that batch will be improperly heat treated. However, the QA department is supposed to catch these problems.

Years ago, I purchased a 24" plane (copy of Stanley #7) from Record which was never stress relieved--the bottom would not stay flat. Now we all know that Record makes good tools, but not the day that mine was manufactured. Finally, I stress relieved it in a large furnace--it came out with a huge amount of twist. So much twist that I had to use a power sander to remove at least 3 mm of material on the ends. Now it works OK but what a lot of work.

What bothers me is when a manufacturer like Pfeil makes all their tools too soft, year after year. Who do they build these tools for?

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I suggest practicing hardening and tempering on high carbon hacksaw blades (usually the cheapest you can get). Premium blades are usually HSS and do not respond well to heat treating. These blades are small enough to handle easily with a single propane torch and cheap enough to make mistakes on. Start by heating cherry red and letting cool in air to anneal. Then you can shape cold, as a small gouge, knife or whatever. Then heat back to cherry red but quench in oil or water. Water is supposed to make it a little harder and more brittle because it removes heat faster than oil. I use water because it isn't as messy. Then polish and, as Michael said, temper by heating VERY gently well back from the edge until a straw color just gets to the edge. I also recommend shaping the edge before you harden. Once you've done this a few times you may be ready to tackle the gouges. Have fun. Lyle Reedy

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Old Marples tools should be hard enough to use, However some new Marples chisells and gauges need a bit of using befor they become really good. (there is a reason for it)

Sometimes the way we sharpen the tools softens the edge, especially sharpening with speedy grinders.

If you get a bad tool throw it away, it will only go from bad to worse. Hardening and tempering steel is a job for the experts. You would not want a blacksmith to tune your violin?

Cheers Wolfjk

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I made a small set of gouges many years ago from 01 steel, a high carbon tool steel. I bought the unhardened steel in bars, shaped them, hardened them and then annealed them. The package that the steel was wrapped in had a graph that showed what temperature to anneal the steel to achieve a given Rockewell hardness. One thing I found useful was to test the steel after I hardened it by running a file over the surface. If the steel is properly hard the file will just skate on the surface, after it's been annealed the harder file will cut the softer steel.

I quenched my steel in cheap olive oil which gave it a lovely gold color.

If I were you, I'd get rid of the bad tools and buy good ones. I think the process of fixing these gouges is not worth the hassel. Th results you get may not be satisfactory either, since this can be a tricky especially since you you don't know anything about the composition of the steel you're using.


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Originally posted by:


Old Marples tools should be hard enough to use, However some new Marples chisells and gauges need a bit of using befor they become really good. (there is a reason for it)

Sometimes the way we sharpen the tools softens the edge, especially sharpening with speedy grinders.

If you get a bad tool throw it away, it will only go from bad to worse. Hardening and tempering steel is a job for the experts. You would not want a blacksmith to tune your violin?

Cheers Wolfjk

I couldn't agree more with all these points.

I find that I have to sharpen and hone new tools to bring them in line with my expectations. Also, I use a slow, water fed wheel for grinding. Then I hone (wetstone) and strop (leather). If you heat up the gouge or chisel on a fast (bench) grinder, you soften the steel.

Finally, I'd rather spend my time making a violin than heat treating tools. But that's my opinion.

Mike in NJ

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Here is a little blacksmith science of iron-carbon system. At room temperature, iron has a body-centered cubic crystalline structure. It has very little solubility for carbon, therefore nearly all the carbon is precipitated out as iron carbide. When iron is heated above 750 C, it changes into face-centered cubic structure and this crystalline structure has a high solubility for carbon. If you cool it very fast, such as dropping it in water, the carbon has no time to separate out as carbide and distorts the crystal structure into body-centered-tetragonal form. This is the hard form of iron-carbon system. To harden the steel, you heat it to 800-900 C (bright red) and cool it fast. Chromium has strong affinity to carbon, therefore, adding Cr in iron will supress the formation of iron-carbide. Steels like A2 and HSS, can be cool in air and hardened. I made my cutting tools using high carbon steel (1% carbon), A2 (1% carbon, 5% chromium) and HSS. A2 needs to be heated to 1000 C and HSS, 1100 C to harden. A2, although not as hard as plain carbon steel (RC 62 vs. RC 64), the edge does not chip easily as in carbon steel. My fingerplane blades have been used for several years now, and never need to re-grind the bevel.

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It takes a lot of experience to know what kind of steel you have. Absent this knowledge, you may have to experiment. Lots of folks don't know a bright cherry red from a dull cherry red and get the steel too hot. It doesn't help much to know anything about phase diagrams or body-centered cubic structures if you don't have the instrumentation to make use of such knowledge. I have to say I'm in agreement with the points made above. Get the best tools you can for the money and sharpen them carefully so as not to ruin the temper. The exception might be small tools like drill bits. These are fairly easy to harden and re-temper if you know what color to look for--sort of a speckled appearance.

Even some blacksmiths don't have the skills to do certain work--such as tempering springs.

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So we have a strange sort of consensus here: there's a group who hasn't tried it, and say it can't be done, and will tell you how complex it is, and then there are those of us who have done it, and say it can be done, and it's no big deal. I guess you're just going to have to decide who you're going to believe: the people who've done it, or the ones who haven't. If you're in the "I couldn't possibly do something like that" group, please box up all your bad gouges and chisels, and send them to me. :-)

A good place to start learning how to do it, if that's what you want, is The Making of Tools (Paperback)

by Alexander G. Weygers. It's a book for home tool makers and backyard blacksmiths, and Amazon has copies, used. It's where I learned how to harden my gouges.

See also this interesting site about the author:

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Thank you everyone!

After reading all the information you've given me, I think I'll

take the advice of both groups! I'll leave my antique Marples

gouges as they are for now, but will buy the book Michael mentioned

and read internet sites, and try the hardening process at home on

some damaged Footprint chisels which I never use. Once I learn how

to do it and identify the dull cherry red and learn the process,

I'll be able to try it on my softest Pfeil tools. If I manage to

harden them well enough, I'll do my other Pfeil tools.

Having read the posts here, I'm not sure if I should attempt to

harden my old Marples gouges since I expect the handles need to be

taken off first, and I would hate for them to crack in the process

of removing them or putting them back on!... Then again, the book

might give proper techniques for this. I do agree with those who

said I should just buy better tools, however given that's an

option, I may as well try my hand at hardening first. (-: Thanks

again everyone!!

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Some interesting opinions here.

Also signs of "slanging" starting as the forum gets allocated into groups, whether or not they want to or need to be.

So to help the allocation....

My excellent Marples chissel is early 1900's and has not been machine sharpened since it left the factory.

Whilst serving my apprenticeship I had the opportunity to make (as we all did) a set of hand tools, which we machined, hardened, tempered, fitted etc. We also ruined many good tool edges from over-temperature grinding during sharpening with the wheel. We were encouraged to understand what was going wrong and to cover the theory later during metalurgy class.

Later some of us continued into higher education and gained an appreciation of the finer detail of grain microstructures and the influence of temperature, time alloying and working to further explain what we had already experimented with and then learned during apprenticeship.

Possible Cause

The soft tools may have been soft when they left the factory, either on a bad quality day or from the wrong factory using dodgy raw materials and labour. They may have been overheated later by machine grinding with no coolant until they were annealing themselves. Either way they can be recovered by carefully following the process either in Michael's book or in the free reference that I provided above.

They will be made worse or destroyed by blindly cooking then dunking.

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Thanks scratchy rosin. Yes, I was surprised that these old gouges

didn't hold an edge as well as I'd expected them to. It might be

true that one of their previous owners (there a two different owner

names stamped into the boxwood handles) overheated them by

sharpening them on a grinding wheel for too long. They are not

terribly soft, but compared to my Toledo chisels or Lie-Nielsen

blades they dull much quicker and can't be made as sharp.

Incidentally, the Pfeil tools can be honed to a razor edge, but

that edge turns or dents with only light use. I think I will write

to Pfeil and complain since they claim their tools are 60+

rockwell, but they really aren't! No way.

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Yes, and it is very low-tech-- it can be done with a charcoal fire, and a bucket of water. If you need a blower, your tank-style vacuum cleaner will work, if you move the hose over to the exhaust side, and extend the hose with something heat-resistant (metal). A little internet research will give you a good idea of what grade of steel you are looking at, and you can proceed.

Some of my favorite gouges I made from a discarded plow disc. My bass sound-post setter was made from part of a leaf-spring. My violin soundpost setter was made from a smaller spring. Knives were from discarded Sawzall blades, after a remodel job. Planes of wood and steel, or just steel-- I haven't tried a brass one yet.

Blacksmiths were doing this for thousands of years before accurate thermometers were invented.

As Mike said, each to their taste--if you don't like messing with fire and steel, leave it alone, but it really is pretty easy to learn...a WHOLE lot easier than violin making. :-) Grab a book and go for it.


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