Quandary & Conundrum: flatten back of a chisel

[froglips]

I'm an a mental (and somewhat physical) impasse, so I thought clearer minds and those not as close to the situation could tip the scale of a decision.

I have a 2" wide 7" long blade timber framing chisel.

Here is where I'm at......

It was bent, likely from being beaten upon. If I rocked it back, the front lifted almost 1/8".

Well, after way (and I do mean WAY) too much work, I took out the bend and have it "very" close.

Here is the problem. The front 1" x 1" corner of the back is not very close to the rest of the chisel. Call it a low spot.

View image in gallery​

So, do I grind back the front of the chisel, losing about 1" of length? In effect shortening the life and use of the chisel.

or.......

Do I keep working on the back until its close enough for use? I'd be removing a tremendous amount of metal but keep the length.

There are pros and cons both ways. :thumbs_up:confused_:thumbs_do

In either case, this chisel is much loved and will be used. Its not a question of a new one

So, what say you my obsessed brothers in hairy neanderthal arms?

Jim

 

[CarvedTones]

Ouch!

I say grind back for a couple of reasons...

One is that you get the clean edge.

The other is that I think I still see where the bend was and every bit of length removed is leverage reduced and threfore makes it less likely that it will bend again.

 

[Mike Davis]

I had the same problem with an older chisel, maybe it was softer metal. :dontknow:

I straightened it out with gentle taps of a ball pean hammer then flattened a little on a belt sander. I lost very little metal and the chisel works fine now.



edit: that may have been used as a prybar and your more proper use of it may never result in the same distortion.

 

[Gotcha6]

Mike is right. A few taps placed strategically along the opposite side of the chisel at the approximate bend point should stretch that face of the chisel & bring it down. Just keep working at it & be sure you're using a flat anvil opposite. I've re squared framing squares with this method by peening them in or out in the corner.

 

[ebrant]

+1 on straightening it. I'll even help!:gar-Bi

 

[froglips]

Wow, this sounds like a great learning experience and a chance to hit something with a bigger hammer!

Just so I'm clear, the bottom of the chisel is mostly flat accept for that corner.

So ya'll think I can bend just that corner?

Jim

 

[Mike Davis]

No, we don't think you can. We know we can. :rotflm:

 

[Glennbear]

Just a WAG here but if the tempering/brittleness level of the chisel is low enough that it bent without fracturing in the first place I do not see why it cannot be unbent with judicious hammer and anvil work. :wsmile:

 

[tjgreen]

Jim,
I'd be surprised if you get it perfect, but it seems like you could get it closer than it is now, close enough so you can grind it flat without losing much width.

If you are looking for a forge/anvil/blacksmithing setup in Hillsborough, PM me and I'll send you my dad's info, he's got lots of big hammers. He might also help to re-temp it after you're done bending it.

 

[Len]

Just think of it as a giant Japanese chisel that needs the back flattened (again). Same techniques should work.

Len

 

[junquecol]

Why not heat chisel to red hot, let it cool. Then it will be soft, and can be easily straightened. Then reheat and quench in water. It will be very hard, but also brittle. Then heat chisel to "straw" color and allow to cool. If chisel has removable handle, just put in your oven (preferably when SHMBO isn't home), set on highest setting. After about 30 minutes, turn oven off and allow chisel to cool while still in the oven. Disclamer: My opinions are free, and worth exactly what you pay for them.

 

[willarda]

Bruce's idea is probably best. You do not know how well the length of the blade was tempered. so it is posibly that hammering on it will cause the blade to fracture.

Heating and cooling slowly is called annealing. this will allow the steel to be in a very soft state. However air cooling is not slow enough, more than likely. You need to heat to the critical temp (1450, or cherry tomatoe red) which is the point that the tool steel looses its magnetism. Have a good magnet nearby when you do this. Touch the hot steel to the magnet and if it does not stick, immediately begin the slow cool.

The best way to slow cool is to "quench" the steel in vermiculite. This is an insulator and will slow the cooling process considerably. Just jab the tool into a can of the stuff.

When you get ready to harden, heat the tool up to the same temperature, then cool in oil (I use peanut oil), moving the blade up and down in the oil to spread out the hardened area (you do not want a sharp transition from hard to soft steel).

For tempering, the range of temperatures appropriate for tool steel is generally in the range of 325 to 450, just the range of those small bench top ovens. Get an oven thermometer, because the dial indicators on the ovens are rarely accurate. Start out at 350 degrees or even lower, and heat the blade for at least 15 minutes at temp. You can go as long as you like with no change in effect. Test the blade with a file to see if it has softened enough to be cut by a file. Creep up on the desired temp in 25 degree increments or so. You want a good compromise between hardness to take and edge, and softness to prevent chipping and to allow honing, etc.

 

[Dean Maiorano]

Bill,

How does the peanut oil respond to iron that's been heated to 1450°F? Peanut Oil has a smoke point of 450°F, a flash point of 620°F and a fire point of 670°F; isn't there a risk of flames/fire at such a higher temperature? If so, what precautions do you recommend when applying your re-hardening process?

Thanks,

Dean

 

[CarvedTones]

I am not Bill, but I have quenched hot metal in oil. You use a lot more oil than steel and move the steel around a lot when you first put it in (but don't hit the sides of the container). The idea is to cool the steel rather than heating the oil. In reality you will do both but as long as you have a much greater mass of oil than steel the heat will disappate fine without bringing the oil anywhere near ignition temps.

 

[willarda]

Andy is right. If you just dropped oil onto the steel, you would probably get a fire. It is not uncommon when you first stick the hot steel into oil (motor oil for example) that you will get a very short lived flash of flame. You will always get some smoke in any case.

I ALWAYS do this outside on a metal table, well removed from any flammable objects. Do not do this inside of your shop or your house, etc. I can not emphasize this enough! In addition, I use leather gloves and I have good eye protection (a face mask) and appropriate clothing in case of splatters, etc. Sticking hot metal into oil is not an intuitive activity, but as Andy said, the oil quenches itself due to the large volume of oil and the fact that you move the steel around in the oil.

If you have not done this before, I would suggest that you do it with someone who has done it before, and/or make some practice runs to see that your work flow is efficient and safe.

 

[Dean Maiorano]

Andy + Bill,

Thanks for the advice. I'm not the OP but I've considered venturing more into the metal side of woodworking and your post took me a step closer. I only work safe and only work well informed; I will seek additional literature, videos and tutelage.

Dean

 

[CarvedTones]

Dean,

Traditionalists will wail about this, but there really isn't a lot to be gained by using oil over water:

Water is one of the most efficient quenching media where maximum hardness is acquired, but there is a small chance that it may cause distortion and tiny cracking. When hardness can be sacrificed, whale, cottonseed and mineral oils are used. These often tend to oxidize and form a sludge, which consequently lowers the efficiency. The quenching velocity (cooling rate) of oil is much less than water. Intermediate rates between water and oil can be obtained with water containing 10-30% Ucon, a substance with an inverse solubility which therefore deposits on the object to slow the rate of cooling.

That is from a Wiki article. I usually use either water, motor oil or mineral oil.

 

[Mike Davis]

But, you need to know the metal. There are air, water and oil hardening steels. Best to match the method to the material.

That said brine is much better than plain water. And preheating the water will reduce surface cracking.

 

[willarda]

If you are interested in metal working and tools, you might contact Peter Ross out in Silk Hope who might be intersted in some instruction, etc.