Heat Treating Old Chisels

[maswindell]

I have been collecting and refurbishing old chisels to resell mostly and keep the good ones. I have noticed that there seems to be a wide variation of hardness in the various brands. I bought a diamond plate with 400/1000 grit to ease the sharpening pain. I have DMT plates coarse,fine,very fine and they do seem to work well. Luckily I bought these 20 years ago and now they would be out of reach. Anyway I have a few Witherby chisels 1/2 and 3/4 that resist sharpening even on the new diamond plate ! I wish I had a hardness tester as these 2 are harder than I have seen before.

How did the old tool makers heat treat and keep the temperature consistent. I assume the quench had a lot to do with the steel hardness and how it was done-water,oil ? I'm no blacksmith or knife maker just curious about how these toolmakers regulated temperature and quenching. For the most part the steel seems to be uniform for maker to maker so I wonder if the tool makers bought billets from steel foundrys as opposed to making steel in house.

Cheers
Mike

[AHill]

First of all, the chisels were almost all forged.  So, they would be heated up over 1900 deg F and worked until the temp dropped to around 1600 deg F.  The guy doing the forging could tell the temp by the color of the steel and how well it was forming in the die.  Once formed, the chisel would be heat treated, then machined to final dimensions.

A typical heat treatment sequence for the tool steels they used then (and even now) was to slowly heat to around 1200 deg F, then raise the temp to around 1450-1500 deg F.  Hold for 10-30 min (depends on the mass of the part - for chisels probably closer to 10 min, then oil quench.  Then temper the steel.  As quenched (no tempering), O1 steel has a Rockwell C hardness of 63-65, which is too brittle for an edge tool.  Chisels are around Rc 60-62, which would require tempering at around 450 deg F for a certain time (depends on the mass of the tool), then let it air cool.

Temps of furnaces / ovens were controlled by operators.  They used thermocouples to monitor temps.  Most ovens used natural gas for a heat source.  Variations in steel composition, exact temperature of the furnaces, length of time at each temp, etc. all cause variations in the hardness of the final product.  The process is the same for water quenched tool steels.

Processes for steel making and heat treating are much better controlled today than back in the day.  Temps and times may be different for different alloys.  Most chisels from the late 1800's up to the early 1900's used proprietary steel developed by the company.  Hard to tell exactly what their heat treat procedures were, but I'm guessing it's very similar to what I described above.

It's also possible the differences you see are artifacts of how the owner of the chisel may have ground the chisel when sharpening.  Most owners knew you could ruin the temper if the chisel got too hot, so they would periodically immerse the chisel in water to cool it off.  If you get it too hot, then quench it in water, you risk getting a very hard and brittle edge.

Here's a good abbreviated article on the process:
https://northmen.com/en/creating-process...arp%20edge.

[wmickley]

I have been collecting and refurbishing old chisels to resell mostly and keep the good ones. I have noticed that there seems to be a wide variation of hardness in the various brands. I bought a diamond plate with 400/1000 grit to ease the sharpening pain. I have DMT plates coarse,fine,very fine and they do seem to work well. Luckily I bought these 20 years ago and now they would be out of reach. Anyway I have a few Witherby chisels 1/2 and 3/4 that resist sharpening even on the new diamond plate ! I wish I had a hardness tester as these 2 are harder than I have seen before.

How did the old tool makers heat treat and keep the temperature consistent. I assume the quench had a lot to do with the steel hardness and how it was done-water,oil ? I'm no blacksmith or knife maker just curious about how these toolmakers regulated temperature and quenching. For the most part the steel seems to be uniform for maker to maker so I wonder if the tool makers bought billets from steel foundrys as opposed to making steel in house.

Cheers
Mike

Chisels were made somewhat differently in 1900 than in 1800.

In 1800 chisels were formed by blacksmiths. They were heated to the critical temperature, which was judged by eye, then quenched in water for hardening. They were then tempered by heating up to an intermediate temperature to make them less hard and less brittle (tougher). This temperature was judged by oxidation colors on the surface of the steel, ranging from light yellow (lightly tempered), through orange, bronze, purple, blue, and grey. Again judged by eye. Chisels making was usually not done by a village blacksmith, but rather a specialist who did just chisels, so he could make them faster and better.

After industrialization, chisels were drop forged. A blank was placed over a die and hammered by a heavy machine to conform to the die, or series of dies to make the chisel shape. Heat treating was done in furnaces with controlled temperatures. 

Drop forging is still done today for large scale manufacturing. Companies like Lie Nielsen, Lee Valley and Blue Spruce machine chisels from bar stock. This is a much more expensive process than drop forging, but can be done on a smaller scale. They are also limited to steels that machine well.

Personally I have gradually switched over to all English chisels from before 1850, since I can get a very fine, long lasting edge.

[Timberwolf]

Chisels were made somewhat differently in 1900 than in 1800.

In 1800 chisels were formed by blacksmiths. They were heated to the critical temperature, which was judged by eye, then quenched in water for hardening. They were then tempered by heating up to an intermediate temperature to make them less hard and less brittle (tougher). This temperature was judged by oxidation colors on the surface of the steel, ranging from light yellow (lightly tempered), through orange, bronze, purple, blue, and grey. Again judged by eye. Chisels making was usually not done by a village blacksmith, but rather a specialist who did just chisels, so he could make them faster and better.

After industrialization, chisels were drop forged. A blank was placed over a die and hammered by a heavy machine to conform to the die, or series of dies to make the chisel shape. Heat treating was done in furnaces with controlled temperatures. 

Drop forging is still done today for large scale manufacturing. Companies like Lie Nielsen, Lee Valley and Blue Spruce machine chisels from bar stock. This is a much more expensive process than drop forging, but can be done on a smaller scale. They are also limited to steels that machine well.

Personally I have gradually switched over to all English chisels from before 1850, since I can get a very fine, long lasting edge.

..........................
I would just say that "old" chisels were sharpened by old time users that may have overheated the steel when sharpening them over many years so you never can tell how well they will hold an edge until you test them. "Old" doesn't necessarily mean "good"..They made junk in the olden days too! They knew what their markets could afford. The "Harbor Freight" concept of marketing isn't new.


Warren pretty much nailed it...particularly for the forged chisels. Here's a pretty detailed video showing the process...

https://www.youtube.com/watch?v=r4RhucJ831I

[maswindell]

..........................
I would just say that "old" chisels were sharpened by old time users that may have overheated the steel when sharpening them over many years so you never can tell how well they will hold an edge until you test them. "Old" doesn't necessarily mean "good"..They made junk in the olden days too! They knew what their markets could afford. The "Harbor Freight" concept of marketing isn't new.


Warren pretty much nailed it...particularly for the forged chisels. Here's a pretty detailed video showing the process...

https://www.youtube.com/watch?v=r4RhucJ831I

The video were really eyeopening to the making of chisels. I guess I wasn't clear in my post about the hardness that I have found in a few Witherby's. I know the cutting edge can get ruined by overheating but the chisels that I have are hard the whole length not just at the cutting edge. A new file just slides off the chisel anywhere from tip to socket. I am asking the roundabout way how often did tools get heat treated wrong and slip thru the processing. I think these 2 chisels probably need annealing to make them usable but I am unable to do that. Thx for the vids.

[Timberwolf]

The video were really eyeopening to the making of chisels. I guess I wasn't clear in my post about the hardness that I have found in a few Witherby's. I know the cutting edge can get ruined by overheating but the chisels that I have are hard the whole length not just at the cutting edge. A new file just slides off the chisel anywhere from tip to socket. I am asking the roundabout way how often did tools get heat treated wrong and slip thru the processing. I think these 2 chisels probably need annealing to make them usable but I am unable to do that. Thx for the vids.

...........
A chisel with full length hardening is a plus IMO....I still use the old method I learned as an apprentice in the machine shop...just anneal the edge with a propane torch..Shine the metal up with sandpaper, then apply the flame a couple of inches ABOVE the part that needs tempering letting the heat FLOW down towards the edge...When an inch above the edge turns straw yellow in color, quench it in water.. At that point you should just barely be able to scratch it with a sharp file. OR, even easier, if you can remove the handle, just set your oven to 350/400 degrees, put the chisel inside and leave it for about half an hour. That should get the hardness down to about 59/60Rc. Test it by chiseling it into some hard wood..if the edge folds or chips, hone a micro-bevel on it...That should make a very good chisel.

[maswindell]

...........
A chisel with full length hardening is a plus IMO....I still use the old method I learned as an apprentice in the machine shop...just anneal the edge with a propane torch..Shine the metal up with sandpaper, then apply the flame  a couple of inches ABOVE the part that needs tempering letting the heat FLOW down towards the edge...When an inch above the edge turns straw yellow in color, quench it in water.. At that point you should just barely be able to scratch it with a sharp file. OR, even easier, if you can remove the handle, just set your oven to 350/400 degrees, put the chisel inside and leave it for about half an hour. That should get the hardness down to about 59/60Rc. Test it by chiseling it into some hard wood..if the edge folds or chips, hone a micro-bevel on it...That should make a very good chisel.

Thanks for the tip about tempering, I just put a handle on them so I'll try the propane torch route.
THX

[adamcherubini]

...........
A chisel with full length hardening is a plus IMO....I still use the old method I learned as an apprentice in the machine shop...just anneal the edge with a propane torch..Shine the metal up with sandpaper, then apply the flame  a couple of inches ABOVE the part that needs tempering letting the heat FLOW down towards the edge...When an inch above the edge turns straw yellow in color, quench it in water.. At that point you should just barely be able to scratch it with a sharp file. OR, even easier, if you can remove the handle, just set your oven to 350/400 degrees, put the chisel inside and leave it for about half an hour. That should get the hardness down to about 59/60Rc. Test it by chiseling it into some hard wood..if the edge folds or chips, hone a micro-bevel on it...That should make a very good chisel.

I think you have some of this a little sideways.

Lots of woodworkers believe differential hardening, either by hardening only a portion of the tool, or laminating high carbon steel to iron provides shock absorption which prolongs edge life and makes for a better chisel. Japanese chisels makers talk about this. Hardening the entire tool is the modern, easier method.

You can't anneal any steel with a propane torch. At least, not without some sort of forge. The process you describe sounds like tempering which could only soften steel by heating above the temper temperature. Quenching after tempering does nothing. And when tempering, you just have to heat through, I don't think (could be wrong) long soaks do anything.

Hand forging vs drop forging...hand forging generally reduces steel grain size allowing chisels to take a keener edge. And it greatly improves the strength of dirty or non-homogeneous steels.

I've been using hand made chisels for many years and I prefer them. For carpentry, which has taken up much of my time these last several years, I use the cheapest chisels on the planet and I've found I like them (S#60s). I still admit to being a chisel snob, however. And pedantic (sorry guys).

Adam

[Timberwolf]

I think you have some of this a little sideways. 

Lots of woodworkers believe differential hardening, either by hardening only a portion of the tool, or laminating high carbon steel to iron provides shock absorption which prolongs edge life and makes for a better chisel. Japanese chisels makers talk about this.  Hardening the entire tool is the modern, easier method.

You can't anneal any steel with a propane torch. At least, not without some sort of forge. The process you describe sounds like tempering which could only soften steel by heating above the temper temperature. Quenching after tempering does nothing. And when tempering, you just have to heat through, I don't think (could be wrong) long soaks do anything.

Hand forging vs drop forging...hand forging generally reduces steel grain size allowing chisels to take a keener edge.  And it greatly improves the strength of dirty or non-homogeneous steels.

I've been using hand made chisels for many years and I prefer them. For carpentry, which has taken up much of my time these last several years, I use the cheapest chisels on the planet and I've found I like them (S#60s). I still admit to being a chisel snob, however. And pedantic (sorry guys).

Adam

...............................
You can't anneal any steel with a propane torch. At least, not without some sort of forge. The process you describe sounds like tempering which could only soften steel by heating above the temper temperature. Quenching after tempering does nothing. And when tempering, you just have to heat through, I don't think (could be wrong) long soaks do anything

Trying not to sound argumentative here...but I can anneal springs with a propane torch and make them worthless....Or I can MAKE springs with a propane torch...I don't need a "forge"..I can do it using a clay flower pot if I can't generate enough heat in open air..I can also lay it on a bed of charcoal briquets..or on firebrick, or an asbestos board..or a firepit...most anything that will reflect the heat where I want it. I can take a soft carbon steel and harden the surface just like frontiersmen did the frizzens of their rifles....I generally agree with you that long tempering soaks are not much more effective after the desired temperature is reached...I have made hundreds of leaf springs and coil springs, both tension and compression...it was one of my jobs after school as a kid in a local machine shop. I worked there four years..I was the base machinist for two years at Parris Island Marine Base. Also made and repaired cutting tools of all types..and hardened parts using cyanide. I don't have much knowledge in regards to more "modern" steels... I can get by but I am certainly no metallurgist and don't make that claim..I will be 90yrs old in September and still have my acetylene torches and home machine shop, with way too many machines than I have room for..One of the things I can still do when I feel well enough is make wood carving knives and I have lots of machines that I use in making them...but when I was younger I made lots of hunting knives. I was working with steel long before I ever worked wood and spent my entire working life doing so. My body is weak now, but I thank God my memory is still good...My apologies if I came across badly..I did not intended to be rude.

[maswindell]

I think you have some of this a little sideways. 

Lots of woodworkers believe differential hardening, either by hardening only a portion of the tool, or laminating high carbon steel to iron provides shock absorption which prolongs edge life and makes for a better chisel. Japanese chisels makers talk about this.  Hardening the entire tool is the modern, easier method.

You can't anneal any steel with a propane torch. At least, not without some sort of forge. The process you describe sounds like tempering which could only soften steel by heating above the temper temperature. Quenching after tempering does nothing. And when tempering, you just have to heat through, I don't think (could be wrong) long soaks do anything.

Hand forging vs drop forging...hand forging generally reduces steel grain size allowing chisels to take a keener edge.  And it greatly improves the strength of dirty or non-homogeneous steels.

I've been using hand made chisels for many years and I prefer them. For carpentry, which has taken up much of my time these last several years, I use the cheapest chisels on the planet and I've found I like them (S#60s). I still admit to being a chisel snob, however. And pedantic (sorry guys).

Adam

Well thanks for the info and now I am confused. I have 2 witherbys and one noname which afile wont even scrape the surface-not just the cutting edge the whole chisel. What do you suggest I do tomake thes chisels usable. Unfortunately I already have put handles on all 3. What can a do to anneal these chisels ?