Thread: Your experiences with re-hardened chisels

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This includes cute little ovens, amazing grinding belts and some very interesting metal things (I've been thinking about incorporating into box making)

If you join some of the knife forums on Facebook they discuss in great detail the processes from A to Z. They are an amazingly sharing bunch.

Originally Posted by IanW

Well, it isn't a big trend that I'm aware of, but you might have planted a seed or two here, John!

Did the guitar-maker bloke post his method, and if so could you put up a link, please? I'll probably never get around to building that forge I've been thinking about for at least 25 years, but you never know......

Cheers,

Apologies for jumping in and doing the task asked by Ian for you truckjohn . I went and found this link .

Harden Up (your chisels) - Australian/New Zealand Luthiers Forum

Rob

Thanks, Rob.

However, after reading the post, I'm totally nonplussed. If he's only heating to 750 C, then he's barely reaching the conversion temperature for medium-carbon steel. Given that he's using a couple of butane torches, that would probably be about the limit you could get, with something the size of a chisel. I would think the sort of high-carbon steel in a chisel would need to go a couple hundred degrees higher to dissolve all the carbides, according to what I read. Another poster on the site suggested he was actually annealing his chisels! However, that doesn't make sense either, since he specifically says his chisels were turning up their noses on Gidgee before, and now they are holding their edge fantastically, so they must've gotten harder.

Can someone explain???

Cheers,

Personally I think it's unlikely that anyone could produce a better heat treatment on what is to them an unknown steel than the manufacturer who knows exactly the what the steel is and how to achieve the best heat treatment. Not to mention the imbalance of resources and equipment, too.

Originally Posted by IanW

Thanks, Rob.

However, after reading the post, I'm totally nonplussed. If he's only heating to 750 C, then he's barely reaching the conversion temperature for medium-carbon steel. Given that he's using a couple of butane torches, that would probably be about the limit you could get, with something the size of a chisel. I would think the sort of high-carbon steel in a chisel would need to go a couple hundred degrees higher to dissolve all the carbides, according to what I read. Another poster on the site suggested he was actually annealing his chisels! However, that doesn't make sense either, since he specifically says his chisels were turning up their noses on Gidgee before, and now they are holding their edge fantastically, so they must've gotten harder.

Can someone explain???

Cheers,

Ian.
I've be following along and I'm no metal expert.
As you know.
But I would guess we may be just getting a surface harding going on here.
Quote a quick heat with torches than an oil quench.
I would need to read up a bit more
But we may just be getting the surface hard
Just my two bites worth
(Out of edit time tonight sorry)

Cheers Matt



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Originally Posted by IanW

Can someone explain???

Cheers,

Ive hardened and tempered springs Ive made . Re hardened and tempered drill bits and hollow chisels for my chisel mortiser .Made router bits with flat file welded and brazed to rod then annealed. All have worked and lasted once I got it right . The first springs snapped so I lowered the initial hardening temp and they worked. I had a old plane blade that was tool steel taken from a 100 year old plane that I could not get to work and never figured out.
I have never needed to do fine woodwork chisels though because I have plenty . My son does have a set of Irwin's I think . And they are crap . The edge is soft and folds just like Trevor describes in his hardening thread.

The way I see it from what I have read and practiced, the heat, the Cherry colour 750 degrees that Trevor describes is right and is even higher than recommended in one of my books for a cold chisel.

The description by Nick in that thread isn't like anything Ive read or practiced with annealing of tool steel.

If you wanted to anneal the chisel you would heat it . I think the cherry colour is fine for that ? I would think any red colour dark or bright would do ? But ready for correction there . And then you would cool the tool steel as slowly as possible . I like burying it in saw dust in a container with an air tight lid . Ive done it in sand as well . And I know the more knowledgeable guys have better suggestions with annealing, but its what I have at hand for annealing.

I might give my sons Chisel a try . I have wondered if it could be done .

Here is one of my books on the subject . A good book to have . The Modern Blacksmith by Alexander G Weygers.
It describes Three methods of hardening tool steel.
Trevors description looks the same as the first simple method where a lower first heat is made then quenched and no tempering after that. The cold chisel is being quenched in water rather than oil though. The oil should give the chisel a softer cushion of steel internally with a hard outside surface . The next more refined methods where tempering is done start with the first heat being higher.
IMG_3494.JPGIMG_3492.JPGIMG_3493.JPG

I wouldn't try it with butane torches either , I used Oxy and Acetylene or the forge. A simple small hair dryer forge should be able to be quickly set up for trying this out .

Rob

Originally Posted by auscab

Apologies for jumping in and doing the task asked by Ian for you truckjohn . I went and found this link .

Harden Up (your chisels) - Australian/New Zealand Luthiers Forum

Rob

Yep. Trevor Gore is the one I got this idea from. He also posted the process over on a thread I started on the Official Luthier's Forum and pointed me in the right direction.

The difference is that they were way too chippy for me as quenched - so I tempered them at 400F.

A caveat here.
This only works right on a fairly narrow class of steels. It just so happens that this same class of steels are used in the high volume wood chisel making process...

Due to the volume - they can't spend hours and hours on the heat treatment... That limits the steels somewhere between 5160 and 1084. These steels don't need a long soak at a specific temperature like 1095, W1, O1, or 52100 to get the proper conversion.

Ironically - it appears that my success with this was due to the cheap chisels rather than expensive ones.

Quick torch heating and is going to work better on "cheap" chisels than expensive, "good" alloy ones because the alloys used are picked from the start for fast heat treatment. The better steels are going to require using a proper kiln and a long soak time at the critical temperatures to get the proper sort of results.

So... Following the method over on ANZLF...

Heat to nonmagnetic
Count past 10 while keeping it the same color while its nonmagnetic.
Quench in warmish oil (90-130F). Canola is the best choice for people like you and me.... But olive, peanut, and soybean also work. If you do heat treatment - Parks #50 and MSC 11 second oil are much better choices.

Temper in 400F deep fry oil for a good hard chisel that's not likely to split in two...

Warnings:
It will warp your chisel. Most of the time - they warp back towards the bevel.

Quench up down up down in your oil.... Don't stir round and round or it will warp your chisel sideways.

Don't get greedy. ONLY harden the first 20-30mm of the chisel (about 1"). This reduces the warp you will have to grind back out.

OK, I think I get it. What I read on conversion temps was for the 'fancier' alloys. If the steels that you are talking about convert at lower temperatures in less time, then no problems. However, I have never met a steel that would tolerate much impact in its as-hardened state, so I'd think some degree of tempering would be a necessity for chisels. Being colour-blind, I just can't do it at all reliably by heating to the various subtle colours recommended, so it would have to be an oven-soak for me. Off with those plastic handles, then.

We used to use an old tub filed with pot-ash for annealing, on the farm. I've used sawdust too, but it's a bit more alarming when you plunge the red-hot metal into it and it bursts into flame! To anneal non-precious items like old files, just chuck 'em in your wood heater and dig them out of the ashes next morning - they come out nice & soft & workable.

Rob, I recently tried to harden some old plane blade with no success, too. I made a couple of small (1/4" wide) skews from a thick old worn-out tapered plane blade, which had been sharpened back to about 1/16" from the centre slot! It would probably have been at least 100 yrs old, too, at a guess. I cut the skew blades out & shaped them with what had been the top of the plane blade as the cutting ends of the skews, which gave them a nice shape. The upper part of the old blade was very soft and easy to shape with a file. When I tried hardening them (using a MAPP gas torch, which got them to yellow), they just would not harden. I used oil to quench, at first, hoping to get them hard, but not too hard, so I could avoid tempering, but even water quenching didn't work. My first thought was that it had been a two-piece, forge-welded blade, originally, and the hard steel had been ground away, so what I was working with was the low-carbon top material. Many sources tell you how you can figure out what you've got by observing the colour & patterns of the sparks when you grind it, but when I compared the old plane blade material with various other old blades, I only succeeded in thoroughly confusing myself. At that point I decided my deep ignorance of metallurgy was too much of a handicap, so I put them aside until I can find time to learn a bit more.......

Cheers,

On your old iron - could have been a laminated iron with a sliver of high carbon steel welded to a wrought iron/low carbon base. Those won't harden once you use up the laminated section.

Another possibility is that you decarbed it by heating too much/too long above critical... These thin 2.5mm thick irons will decarb in a hurry once you get them up to temperature...

If it won't harden in brine - it won't harden.... And there's no sense fooling with it any further.

On the color matching.
I heated to nonmagnetic for hardening and a thermometer in a deep fry pot to temper rather than the colors... The color you see depends heavily on both the ambient light conditions and how fatigued you are.

Thanks

Yeah , the blade I used was the two piece forge welded/ laminated type . It was from an old beech Jointer and I made sure it had plenty of the tool steel left in its cutting end. Easy to see when polished up .
I tried at three different hardening temps from low to high and it did nothing . Put a file to it and it was soft . Maybe it was decarbed. If so it either was before I got it, or it decarbed very quickly on my first low temp try .

I did a pair of Skews as well Ian , from a leaf spring . Roughed them out from the spring with the Oxy / Acet cutting torch , a lovely tool to play with in itself . I recently swapped from Ocy / Acet to Oxy / LPG which is even better at cutting but cant weld steel like Acetylene .
I read it couldn't weld in quite a few places on forum and elsewhere but had a job where I needed to do a fine weld and tried to do it . And just like I read , It cant be done .
And after more reading and seeing what happened in front of my eyes I understand exactly why.
It actually turned into a great learning experience where I now under stood more about why in heat welding in a forge ( which I have tried with an extremely low rate of success ) the books say to reduce the air being pumped into the forge to reduce the oxidization and allow a heat weld to happen. The same extra Oxy needed to run an Oxy Lpg oxidizes the metal and you end up with inclusions of oxidized metal in the attempted weld. Getting way off point .
Any way , the leaf spring skews worked great and two stage heat treatment went fine as well. They are a bit chunky and some nice longer refined ones would be nice, as usual I needed them quickly for a job so was in a hurry .

Rob

Originally Posted by truckjohn

......On your old iron - could have been a laminated iron with a sliver of high carbon steel welded to a wrought iron/low carbon base. Those won't harden once you use up the laminated section.....

Yeah John, I reckon that's got to be the reason. It must've been difficult to produce high-carbon steels back in the mid-to-late 1800s. Mucking about forge-welding bits of metal together to get a blade must surely have added an appreciable amount to the cost of production, but not as much as using the hardenable steel for the whole blade, 'twould seem. I made another pair of skews from some HSS bought from a local supplier. They take & hold a good edge, but are a little bit brittle and the fine points break a little too readily. So I'd like to come to grips with the art of tempering, some day.

Seems like we have trodden many similar paths, Rob! I used some old leaf-spring to make myself a couple of draw-knives many moons ago. (In fact it was 1981, 'cos I was home from Canada, visiting the folks and decided to take advantage of the wonderful scrap-metal pile on the farm). I had no trouble annealing and re-hardening the leaf-spring material. More by good luck than good management, I even got the temper just about perfect with the straight one, and just a teeny bit softer than I'd like on the curved knife, but both have been handy tools to have....

Cheers,

Those old high carbon steels didn't need high heat as much as long soak times to treat them properly.... There was no chrome or tungsten to move around - only carbon.... High heat pushes grain growth and decarb like crazy.... They need a solid half hour at nonmagnetic + 30 degrees. And that's hard to do without a kiln...

If I was going to whomp up my own home made plane iron today - I would buy a new production Buck Brothers 1 1/2" or 2" chisel and cut the handle off. Heat the first 1" to nonmagnetic, oil quench and temper.. And off you go.

Option 2 is to start with New Jersey Steel Barron 1084 (it's got a pinch of Vanadium to control grain growth) and go from there. It's a eutectic steel - so you just normalize, heat to nonmagnetic, count to 10 and quench in warm Canola oil... Temper to make you happy and off you go..

Sure - there's theoretically a slight loss of edge life vs O1/W1/1095 from the 0.15% less Carbon.... But in reality - it's more likely to come out properly hard. 1084 is ridiculously easy to heat treat correctly with a torch/forge vs O1/W1/1095 which is tricky for hobby folks to get right without $2,000+ worth of kiln equipment...

You must be John C. Cox from the SMC FORUM. Re-hardened inexpensive chisels vs "good" chisels

Re-hardened inexpensive chisels vs "good" chisels

Hey guys. New guy here.

My primary wood hobby is building acoustic guitars - so I primarily use chisels for paring sort of things, not pounding sort of things. And hard exotic woods are commonly used...

As such - I generally feel like my chisels are too soft, not too hard...

I have recently chased down the rat hole of re-hardening chisels... Without too much preamble here - I found that the Buck Brothers chisels found at the local BORG harden fabulously by heating a smidge past nonmagnetic and then quenching in olive oil. My older Footprint chisel did as well.. They are made of some sort of oil hardening good steel...

(Narex, some sort of German chisel (probably W1), and Harbor Freight wood chisels require water quench.. After making a bunch of banana chisels and cracked chisels - I have decided that water quench is too much trouble)

I decided I liked them much better when not crumbly hard - so I tempered them back at 375F to 400F to get a nice hard edge that doesn't chip immediately.. They are certainly harder now than out of the box - I can easily scratch a box chisel with one of mine now.. And the standard chisels don't mark mine.

But... This whole thing has me thinking..

Is the performance of these re-hardened chisels any better than "Good" chisels? Is Quenched and Tempered $10 Buck Brothers chisel steel anywhere close to that of Veritas O1 or Hirsch steel right out of the box?

I know I am not the only one who has ever tried this out... I know that several of you guys here have done this... Is this something worthwhile...

Thanks