Blade edge fracturing

[JesseM]

I am making a panel gauge and decided to use a knife for scoring. So took one of the indian plane blades I had around and proceed to cut a bit out of it. I ended up using a dremel tool and then shaped it up with sandpaper. At some point it got hot but definitely not red hot. I got to the point of sharpening it up and started noticing the edge fracturing on the diamond stone. I sharpened it up as best I could and the wood fractured it too. So is this just the indian steel or did I do something to mess up the edge? Its not blue or anything like that.

I looked at it with a magnifying scope and there are spots around that looks like air pockets. Didn't see anything like that on the edge, but I may just be missing it or something.

 

[GEPPETTO]

Hi JesseM,

I had, I think, the same problem as you here. Because things of greater cause as you can see here :roll: I had put aside that blade but before of that I grinded a lot the bevel and I think that problem could resolve. The teeth are almost disappeared . I think all could be happened because the lost of the temper caused from a heat.
Try to grind more the bevel.

Cheers
Gabriele

 

[JesseM]

Hi JesseM,
I think all could be happened because the lost of the temper caused from a heat.
Try to grind more the bevel.
Cheers
Gabriele

Thats what I was thinking too, but I would have thought it would have made it softer not more brittle. I was unable to cut the stuff with a hacksaw or drill it. Both just scratched the surface.

I am gonna try again with a different blade. Hopefully it will be different.

Thanks!

 

[Frank D.]

I'm no expert,
But it could be that the steel developed micro-cracks when you cut it. I've heard of this happening when you heat too much then dunk in water. Just a wild guess on my part that this may have happened.

 

[JesseM]

I'm no expert,
But it could be that the steel developed micro-cracks when you cut it. I've heard of this happening when you heat too much then dunk in water. Just a wild guess on my part that this may have happened.

Actually I did do that a few times while shaping it up. That may explain it.

Thanks

 

[Frank D.]

I've been told this a few times by people who know a lot more than I, so I try to avoid it. When you grind tempered steel and it gets hot enough to make a fizzing sound when you dunk it in the water, you either shouldn't dunk it in water or you should grind for less time between dunks. It's not a question of drawing temper, because the blade doesn't have to become blue; it's just the very rapid drop in temperature that can cause the cracks in hardened steel. If you can't help but get the steel quite hot, it's best to let it air cool before continuing. The most efficient way to grind if you're worried about the steel is to do a batch of blades and rotate while they cool on a metal plate. Otherwise take your time and dunk more frequently.

 

[Chris Knight]

Also for shaping metal, use the coarsest stone you can, it will cut faster and cooler. The cutting edge can/must be done with finer abrasives. Do your grinding in a way that allows you at all times to touch the metal without burning your fingers, that way you will be pretty safe and preserve the properties of the steel.

 

[engineer one]

certainly most people when they start with high speed grinders seem to wait until the metal in their hand either feels warm or changes colour, and
this may well be the problem. just hold the cutting edge against the wheel until you can see a change, then either air cool, or dunk, but remember that the water can get warm too, so little and often is the trick.

paul :wink:

or buy a tormek :lol: :lol: :lol: :lol:
sorry could not resist

 

[Bean]

Save your money and dont buy a Tormek, try quenching in oil, does not shock the steel as water does, wipe it off and you can carry on grinding, just quench long before you think it needs it

 

[engineer one]

one thought though bean, one form of metal treatment in the
move toward hard and soft steel is to quench in oil.

a lot depends upon the temperature that you let the edge get to.

so whilst i do not agree about quenching in oil, the principal of
cooling off frequently is a good one.

paul :wink:

 

[Bean]

Paul a lot depends on the shock you induce in the steel when quenching, Water draws the heat from steel very quickly, Oil does not. That is why oil is used for tempering as it does not draw the heat quickly, people are put off oil as it can colour the steel, think balcking before it became a chemical process.
I am sure you are aware that repeated heating and rapid cooling promotes grain growth within the steel, and that to keep a good or fine cutting edge you require small grains, as large grains tend to fracture leading to the the kind of edge problems that prompted this thread.

I must therefore disagree with you Paul

Bean

 

[Anonymous]

Also for shaping metal, use the coarsest stone you can, it will cut faster and cooler. The cutting edge can/must be done with finer abrasives. Do your grinding in a way that allows you at all times to touch the metal without burning your fingers, that way you will be pretty safe and preserve the properties of the steel.

I agree with that entirely. Thats always what I've done. The simplicity of monitoring the heat with a close finger breeds confidence. Shouldn't have to quench in water with enough practise.

But doesn't always hold true. Must remember, that a very thin edge doesn't take much heat to burn. So must lighten up as your blade starts coming to a burr.....or else it may burn prior to your finger feeling it. Shouldn't happen much.

An ALO wheel and dressing is very important in my book too.