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Forum topic by Tim Anderson posted 08-26-2015 01:46 PM 972 views 0 times favorited 12 replies Add to Favorites Watch
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Tim Anderson

152 posts in 1197 days


08-26-2015 01:46 PM

Topic tags/keywords: chisel temper mistake sharpening

So, let’s say, hypothetically of course (who am I kidding, I messed up), that I was grinding a fresh bevel onto a Narex 1/2” mortising chisel, and I happened to lose focus and press down too hard for too long without dipping in water, overheated the cutting edge and ruined the temper of the chisel.

Now whenever I use this chisel, I find that the edge is good for one or two whacks before it buckles and bends along the grain lines, requiring some touchup on diamond stones over and over again to get back an edge.

Is there any way to restore the temper of the chisel so I can use it again? Currently I have access to a propane grill and a propane blow torch, like those that are used for soldering copper pipes, if those will help. Should I just accept that I’ve ruined it and buy another one?

-- -Tim, Salt Lake City, UT, USA


12 replies so far

View bluekingfisher's profile

bluekingfisher

1246 posts in 2446 days


#1 posted 08-26-2015 02:02 PM

Apply heat to the tip with the lamp until it turns light straw colour then quench it in oil. This should bring back the temper.

-- No one plans to fail, they just, just fail to plan

View Andre's profile

Andre

1023 posts in 1272 days


#2 posted 08-26-2015 02:48 PM

Propane will not be hot enough, Map gas is what I use but, usually you need to remove handle and then I leave it in a oven set to 350 deg. F for an hour. Good idea to use a non flammable oil!

-- Lifting one end of the plank.

View rwe2156's profile

rwe2156

2198 posts in 947 days


#3 posted 08-26-2015 03:16 PM

There 3 ways to do it that I know of.

Get your Google on …........

-- Everything is a prototype thats why its one of a kind!!

View CharlesA's profile

CharlesA

3025 posts in 1264 days


#4 posted 08-26-2015 03:26 PM

Isn’t that chisel about $18 new? Seems like a lot of trouble for that price.

-- "Man is the only animal which devours his own, for I can apply no milder term to the general prey of the rich on the poor." ~Thomas Jefferson

View Tim Anderson's profile

Tim Anderson

152 posts in 1197 days


#5 posted 08-26-2015 03:31 PM

Yeah, it does seem like a lot of trouble, but it’s also something I’d like to learn how to do anyways. Since the propane torch I have probably won’t be hot enough, I think I might buy a replacement chisel for now because I have 36 mortises I need to chop in short order (Deadline on the project is in two weeks).

I’ll probably come back and try to repair/restore this one later just to learn and see if I can do it, so I could potentially make my own plane blades or other tools in the future using these techniques. Thanks for the advice so far, everyone.

-- -Tim, Salt Lake City, UT, USA

View SirIrb's profile

SirIrb

1239 posts in 697 days


#6 posted 08-26-2015 04:06 PM

TRANSMISSION FLUID.

Or at least thats what I used to temper knives in. Oil too.

-- Don't blame me, I voted for no one.

View jdh122's profile

jdh122

879 posts in 2284 days


#7 posted 08-26-2015 04:40 PM

You can also re-grind it down past the part that has lost its temper. Just make sure to dress the wheel before starting, press lightly and dunk often.

-- Jeremy, in the Acadian forests

View bobasaurus's profile

bobasaurus

2674 posts in 2650 days


#8 posted 08-26-2015 04:52 PM

You can’t just re-temper it directly as you’ve already softened the steel past the original temper hardness. You’ll have to fully re-harden then re-temper the steel. This involves heating it up to its critical temperature (depends on the steel… usually a cherry red color where a magnet will not stick to the steel), quenching in some liquid or gas (also depends on the steel), then heating it up to the tempering temperature.

Or just grind it back like Jeremy mentioned… much easier overall. Or buy a new one :)

-- Allen, Colorado

View Tim's profile

Tim

3119 posts in 1428 days


#9 posted 08-26-2015 10:59 PM

it would be almost impossible to ruin the temper of the whole chisel by grinding, so I’m with Bob. You probably only killed the temper on 1/4” or something. Grind that away more carefully and dunk in water often and you should be in business no big deal, your chisel lifetime will just be a little shorter. As long as you grind enough to where the steel doesn’t fold when it looks at the wood then you don’t need to grind too much more at first. Then just grind and sharpen a little more often until the softer steel is gone all the way.

View kaerlighedsbamsen's profile

kaerlighedsbamsen

1177 posts in 1180 days


#10 posted 08-26-2015 11:27 PM

Narex chisels are special in that they are made from chrome-manganese steel and shuld be hot-quenched in molten salt before air-cooling in order to be tempered correctly. Read more here: http://www.narexchisels.com/Narex_Chisels/Narex_Cr-Mn_Steel.html
Perhaps a bit difficult to do at home… Heating to cherry red and just cool in air should work as well.

Taking it to the grinder sure sounds easiest.
A trick: FIRST grind away as much material as needed with the blade pointed directly towards the center of the grinding wheel. This way three is a much smaller chance of overhetaing when removing a lot of material. THEN grind a new bevel cooling vigoriously.

Good luck!

-- "Do or Do not. There is no try." - Yoda

View Tim Anderson's profile

Tim Anderson

152 posts in 1197 days


#11 posted 08-27-2015 02:59 AM

Thanks for all the additional advice. I don’t think I have any molten salt baths around. I still plan to revisit the Narex one way or another. The grinder to take off the end seems like a good bet.

I ended up going to woodcraft and bought a more expensive chisel, since I wanted to get to work while I had time. The new one held up just dandy for twelve mortises, and I expect should continue to do so for the remaining 24 on this project.

-- -Tim, Salt Lake City, UT, USA

View bluekingfisher's profile

bluekingfisher

1246 posts in 2446 days


#12 posted 08-27-2015 07:43 AM



Narex chisels are special in that they are made from chrome-manganese steel and shuld be hot-quenched in molten salt before air-cooling in order to be tempered correctly. Read more here: http://www.narexchisels.com/Narex_Chisels/Narex_Cr-Mn_Steel.html
Perhaps a bit difficult to do at home… Heating to cherry red and just cool in air should work as well.

Taking it to the grinder sure sounds easiest.
A trick: FIRST grind away as much material as needed with the blade pointed directly towards the center of the grinding wheel. This way three is a much smaller chance of overhetaing when removing a lot of material. THEN grind a new bevel cooling vigoriously.

He doesn’t have the gear to reach that tempreture (Cherry red). Beside doing as you suggest would leave the steel in a ‘soft state’, air cooling is the method to anneal the steel, exactly not what he is looking to do.

He is only looking to harden the tip where he has over cooked it, so to speak.

From what I have read, the OP wishes to learn how to conduct the operation of saving what is a comparatively inexpensive chisel. He could of course buy new, although he would rather learn how to make a home repair and perhaps save one more item from the landfill.

Good luck!

- kaerlighedsbamsen


-- No one plans to fail, they just, just fail to plan

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