Crumbly Edges

[mudman]

Not long before I finished working in Aylesbury, I paid a visit to the toolman on the market to find hime rummaging through a wooden box of carving tools. He'd just bought them off a lady and I thought I'd struck it lucky when I had a look and found three spoon bents. Whoever had owned them previously obviously needed a few lessons in sharpening but I bought them for a reasonable price and off I went with them.
The next weekend, I squared up the edge of one and proceeded to sharpen it. All went well until I got on to a medium stone and as the edge began to form properly, I was dismayed to see it start to crumble. I could actually break off small chunks with a fingernail.

I guess that the guy had used a grinder on the chisel and overheated it and so ruined it.

Shoved the three in a drawer until tonight when I decided to try another. Same story. No chance of getting a decent edge on it, it just crumbles like the previous one.

I think it's my own fault really. I should have been more aware of what I was buying but I was in too much of a rush to get my hands on them at the time.

Oh well, I don't think I'll even bother with the third. From now on, when it comes to carving tools, I'm going to stick to nice new ones..

 

[JesseM]

I wouldn't give up completely just yet. I had a similar experience recently with a blade I ground out of a piece of hardened steel. Being in too much of a hurry I was dunking in water to help it cool faster. But as some pointed out here I was probably causing micro fractures in the steel from the rapid cooling. The edges were crumbling just as you describe. I took my time after that and eventually got a hard edge. So I guess my point is that the temper might not be ruined, you may just need to grind some more.

 

[mudman]

I fear that the temper may well be ruined. I had to remove quite a fair bit of metal in order to square up the edge before I started to put the edge back on it.
Trouble is that I don't think that there is enough metal left to be left with a usable tool once I grind back far enough to get to decent metal.

 

[Chris Knight]

Barry,
It should be easy enough to restore the hardness if they were decent tools to start with. Just anneal, shape if need be then harden by quenching and then temper the tools. A handheld propane torch is enough for this and if they aren't too large even a domestic gas hob.

 

[Ian Dalziel]

Barry, thiis might help...copied from google


this works for most carbon steels. Aluminum and stainless steels cannot be heat treated with this method.
Material required:
PPE (personal protection Equipement) Safety glasses, gloves, respirator, apron.
5 gal bucket (2)
Enough fireplace ash to fill one of the buckets.
Tongs to handle hot parts.
Source of heat: acetylene torch, forge, etc....
3 gals of used engine oil.
Pot magnet.
To anneal (soften) first heat the part to red heat. Temperature is difficult to gage so use this method. As the part heats, have a magnet handy. There will come a point that the magnet will not stick any more. Hold this temp for a couple minutess and then cool slooooowly. I find that fireplace ashes make an outstanding insulator. It can take up to 12 hours to cool this way. Take the part and bury it in the dry ashes. Check it in a minimum of six hours. Once it is back to room temp, work it as required and then re-heat treat.

To harden, again, heat the part until the magnet will not stick. Hold it there for a few minutes and then immediately quench it in the oil. Use long tongs for this. It will smoke like crazy so do this outside and be careful of spattering oil. This is why you must wear the PPE. Remember that while quenching, keep the part moving. The heat leaves the part and goes into the oil so we want to keep the heat transfer even. At this point we have a hard part but it is also brittle so we need to temper it. Most carbon steels temper nicely at550 to 700 deg so this can be acomplished in an old kitchen oven. I use one that I tweaked the thermostat on and I get 675 out of it.
Temper for 30 min for every inch of thickness. Just turn the oven off and let everything come to room temp slowly.
I have employed this method since the 70's when I learned it from and old time blacksmith. Above all, use caution, care and common sense. IF something does not seem right, STOP!! Aare doing and analyze what you are doing so make the corrections as needed.

you could use a mapp gas torch and not as much engine oil :lol:

I

 

[Alf]

A slightly less dry presentation here.

Cheers, Alf

 

[JesseM]

This is necessary for the hardening to occur but near the surface of the metal those unfaithful little carbon atoms would just as soon run off with any available oxygen-sluts it runs into (oxygen is soooo seductive) and they're lost then forever.

I love this quote

 

[mudman]

Thanks for the links everyone.
I was wondering if it is worth a try and it probably is when you look at the replacement costs. They are/were good tools, one is a Ward, another an Ibbotson and I forget the other make.
It's a shame that they've been abused so as they would have given many more years of use if looked after. The Ward, that I haven't tackled yet, is a #24 that has been ground straight across into a short bent chisel (is that a #21?)
I guess it'll have to be a tuit to try at sometime. Maybe fun.

Jesse,

I did like that quote as well.
I also liked:

Being mainly happy well-adjusted American boys, I think they were hoping that Steve would set himself on fire and run around screaming.