Harden Up (your chisels)

Got a new way of doing something? Or maybe an old method that needs some clarification.

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Trevor Gore
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Harden Up (your chisels)

Post by Trevor Gore » Thu May 19, 2016 11:00 pm

Many of you will have chisels of the Stanley/Marples/Irwin ilk. I’ve had a set of Marples for, idunno, 20 years or so, but was never particularly impressed with their edge holding when used in a guitar building context. My blue handled Irwins were added maybe 10 years ago and they were of similar capability, i.e. not really cutting it.
Irwin-Marples.jpg
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You can see from the pic of the Irwins that I had had a go at hardening the brace carving chisel, with no real beneficial effect. I took to using a variety of old chisels bought at junk sales which performer better, but still not as well as I wanted. I even made a chisel from an old file, which turned out to be the best chisel I owned, holding an edge way sharper and longer than anything else I had.
File Chisel.jpg
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I was just about getting to the stage of junking the Stanleys and Irwins when a correspondence with an old mate happened to mention a method of hardening some of the alloyed tool steels that somehow I had in mind couldn’t be heat hardened. I’d previously tried and failed with the Irwin brace carver and a couple of old Stanley plane blades, which reinforced that thinking. I thought “nothing to lose here”, so give it a go.

The process is to heat the last 50mm of the tool to ~750°C, hold at temperature for ~ 1 minute then plunge it into olive oil. That’s it! To get to 750°C I needed two butane torches flat out and matched the hot steel colour to the chart attached (cherry).
Colour Chart.jpg
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I was expecting some “fireworks” when the blade hit the oil, so tooled up with a stack of safety gear, but was disappointed. Just a bit of mild bubbling. If you try this, I’d suggest that you use all the safety gear, at least the first time around. When the chisel has cooled, clean off the scale (at least) and buff out the discolouration if it bothers you. A previously sharpened chisel will be rather brittle on the cutting edge due to it being so thin (and so cooling too fast) and it won't take an edge. Just grind it back a bit, but keep it cool, then sharpen it up.

Well, I was impressed! I used the brace carver to flush trim a figured gidgee heel cap, reckoning if it could do that well, it would be fine. (The gidgee was some of that “mad” figured stuff from Pete McCurly; hard as the hobs of hell).
Starting heel trim.jpg
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Not only did it flush trim it fine, afterwards it would still shave hairs off my arm without a strop or re-hone. Not even my “file” chisel will do that. So I’d call that a pass. Previously, that chisel would have curled up its toes after one stroke.
Heel cap trimmed.jpg
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Here's a detail of the brace carver after doing the heel cap.
Irwin brace carver.jpg
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I did the rest of the chisels with similar results, but left out the 38mm chisel because I only just had enough heat to get the 32mm one to temperature.
Chisel Set.jpg
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On the wider chisels, if you get the back of the blade into the oil first, you can get the back to dish slightly like some of the Japanese blades, which eases honing.
Dished back.jpg
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Mark McLean
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Re: Harden Up (your chisels)

Post by Mark McLean » Fri May 20, 2016 6:20 am

Nice tute Trevor. My Irwins are not great at holding an edge and I wouldn't mind putting them at risk (and disfiguring them a bit) if it improved their performance. Thanks for the idea and the good instructions.
Mark

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Nick
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Re: Harden Up (your chisels)

Post by Nick » Fri May 20, 2016 9:01 am

To anybody interested in what is going on in Trevor's process you are essentially annealing the chisel. Cherry red or close to it, is the colour most alloy steels anneal at and then the slower quenching in oil rather than water, avoids thermal shock to the steel thereby allowing the molecules in the steel to better 'align' and therefore making it stronger, (think of a piece of chipboard and you hit it on an edge, a piece will break off, now try hitting a board of 'real' wood on the end!). This would explain why they're loosing there edge in the first place, whilst they are 'hardened' at the factory they obviously haven't undergone the full heat treatment process and been annealed! While the steel is technically 'hard' it is still very brittle and prone to chipping out and the extremely thin cutting edge (if you could call a point an edge?) able to break off at a microscopic level. I'd never even considered that this (the heat treatment) process hadn't been followed fully!
A plot maybe by the makers? Don't anneal the blade which saves on production costs plus it has the added benefit of, you the consumer, will constantly be at the grinder & oilstone re-sharpening the chisel thereby wearing it down until you have to go buy a new chisel/set......Hmmmm, interesting. Not saying you still won't have to re-sharpen occasionally but it would be a lot less frequently if you follow Trevor's tute.
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Trevor Gore
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Re: Harden Up (your chisels)

Post by Trevor Gore » Fri May 20, 2016 9:54 am

Nick, before the recent heat treatment the steel was too soft and malleable (formed a "plastic" wire on honing) rather than too hard (forms "dust" on honing as the edge crumbles). I think the manufacturers probably go for a softer, less brittle heat treatment for general purpose chisels so that the edge doesn't shatter when the chisel is belted with a mallet. Mostly, we're looking for chisels to do paring type work, so we want a much harder edge so that it stays sharp for longer and there is much less risk of the edge shattering because there are no impact forces. Or maybe we credit the manufacturers with being smarter than they actually are and they don't have a proper heat treatment process, or if they do it is not under control!! I'm sure these edges could have been a lot harder and the chisel still be used with a mallet. Anyway, I'm pretty happy with how they are now for what I use them for. Much better them them sitting around as ornaments as they did for most of the last 20 years!

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kiwigeo
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Re: Harden Up (your chisels)

Post by kiwigeo » Fri May 20, 2016 11:42 am

Interesting looking chisel rack/junk box there Trevor :mrgreen:
Martin

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Re: Harden Up (your chisels)

Post by routout » Tue May 24, 2016 5:16 pm

Yep I don't think you can go too far wrong with the old chisel they are not that higher grade of steel, the file however I remember getting a slap around the head for doing that to a file machine shop practice :lol:
I was going to make some bent Chisels for Instrument making with a slight bend for pairing down the braces as I have access to the rite steel and a heat treatment place just up the road ,
I do make small inlay ones out of what they call silver steel you can quench harden it after you grind or file it then buff to a mirror finish. I have a selection of carving chisels that stay sharp but most don't want to pay $40 plus for just one they last a life time so the price is not a factor these are polished to a mirror finish they just slide through (fingers as well )all good ,cheers John.
John ,of way too many things to do.

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Re: Harden Up (your chisels)

Post by asgilbert » Fri Oct 19, 2018 7:02 pm

Sorry for the delay in this but only just joined the Forum.
For sake of completeness a Temperature of 860degC quenched in oil would get a better result as the transformation to martensite would be complete and a hardness of around 59HRC achieved, if the material is 1060 as most claim it is. A light temper of around 180degC will pull the hardness back to around 45HRC (much better than the 20 or so HRC I measured mine at) and you will end up with a tool that is not as brittle as quenched.
I am trying to do the same with the irons from my planes... will update on how it goes. I suspect I will end up with significant warping of the Irons! But there you go.
AG

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Re: Harden Up (your chisels)

Post by Andos » Sat Oct 20, 2018 11:54 am

AG, what colour is the steel going to be at 180C.
I've been quenching in water when the steel gets to a dull red to try and get the tool hardness up. Time for a change of technique me thinks!

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Re: Harden Up (your chisels)

Post by kiwigeo » Sat Oct 20, 2018 2:32 pm

Trevor manages to get those Iriwin's hard enough to be useful. Only an Engineer of Trevor's calibre can manage to turn a turd into gold! :mrgreen:
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Re: Harden Up (your chisels)

Post by simso » Sat Oct 20, 2018 6:15 pm

One of my hobbies is making knives from raw material.

It has already been said, but the harder the edge the more brittle it is, I would personally always temper any steel that I quenched

Good save on a cheap set of chisels.

Steve
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Re: Harden Up (your chisels)

Post by asgilbert » Wed Nov 14, 2018 6:32 pm

Obviously not very good at this guys. Travel gets me!! (Just found the notify me when a reply posted)
So the colour of steel being heated to 200 deg C is light yellow. See attachment.
As quenched, steel is brittle and will chip easily... but in the hands of a careful person they are fine. Tempered is better all round.
Damn things take long enough to sharpen... might as well stay sharp for as long as possible I say.
AG
Attachments
Aprox temp of stl by colour.pdf
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Dennis Leahy
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Re: Harden Up (your chisels)

Post by Dennis Leahy » Wed Nov 21, 2018 2:07 pm

Trevor, thanks for this info. Very useful! Two propane torches full bore! ... I wonder about MAPP gas?

asgilbert, can you elaborate on a tempering schedule, and will it work with chisels that have handles (and could not be oven roasted)?
Another damn Yank!

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Re: Harden Up (your chisels)

Post by asgilbert » Wed Nov 21, 2018 2:47 pm

Dennis, In the same way as you hardened them is fine. Use the visual method to gauge temperature as per the previous attachment or use thermo markers if you want to be consistently accurate. A link attached
https://www.weldclass.com.au/product-gr ... kers-chalk

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