Any metal experts on here?

[cornucopia]

hello folks i need to make a special hollowing tool for a vessel i have in mind- i need to create a bent tool which nearly bends back on itself- i know it can be done as David ellsworth makes them for his work.

David uses o-1 drill rod does anyone know if this is available in the u.k or what the u.k equivalent is?

if not i have always used silver steel for my hollowing tools but i have never heated it to bend it does anyone know if this is safe to do or will it make the metal go brittle?

 

[TEP]

Hi George. I'm no metal expert, but I would think it is OK. My understanding is that the metal will only go brittle if you heat it then dump it into a cooling fluid. ie - tempering.

Yet even then if tempered, once you have the shape you require just re-heat and let cool naturally and you will lose the temper. Same principal as overheating carbon steel tools.

 

[mark sanger]

George

Metals are made from various mixtures which give them their main properties. Then they are heat treated to add to this.

From my apprentiship days you heat the metal to cherry red then let it cool slowly in normal air temperature, keep it in the heat for some time say a minute or so.

This will anneal it allowing it to become malleable and you can then bend it. If it starts to cool off heat it again or the bending can cause work hardening as you force the structure which can make it brittle and weak.

Once you have gotten the shape Leave it to cool slowly after keeping it in the heat alows the metal to become ductile and softens it. The metal will then be in it's state before it had any heat treatment. IE soft.

Now when you want to get it hard again you only want to case harden it. So heat it up to cherry red. for a min or two. Then stick it into oil.

If you drive it into water the case hardening will do too deep and can make the tool brittle so it could snap.

However I am now expert on the metology of turning tools. The only thing I would say is that using water to cool it would make it brittle so it may break under pressure and therefore have health and safety issues but using oil, any old oil will do. case hardens it while keeping the integral strength

Like I say this is from memory and I left engineering 20 years ago.

Obviously there is a fire risk with plunging into oil so use a narrow dia container this minimises the amount of flash problems. Do it outside and have a adequate fire precautions ready.

Take care

Mark

 

[mark sanger]

Also and I just thought of this.

Obviously withturning tools we want to keep the cutting edge as sharp for as long as we can. So what I would do once I had bent and case hardened the main tool body. I would heat the tip up to cherry red so that just the top inch is red. then drive plunge this into water. this will give a real hard tip which would be good for grinding a sharp edge and then would hold the edge for longer.


This way the tool body remains strong and won't snap while the tip is as hard as can be to keep the egde.

Mark

 

[jasonB]

You need a high carbon steel to be able to harden & temper it. As luck wood have it "drill rod" is the American term for "silver steel" which is easily available in the UK.

Case hardening of a low carbon steel rod will be a waste of time as after the first regrind the hardened surface will be removed. The process Mark is describing is not actually case hardening, as he mentions oil it is more like hardening gauge plate. Case hardening is where the metal is heated to red hot and carbon added in the form of a powder which becomes part of the molecular structure, as this only hardens the surface it is usually only suitable for sliding surfaces

With the silver steel just heat the working end to cherry red and quench, this will harden the metal but it will be brittle so needs to be tempered. Clean back to bright metal and heat to a med/dark straw colour then quench.

Jason

 

[cornucopia]

thanks for your input chaps

the silver steel is just the shaft of the tool the cutting tip is in hss which is inserted into a drilled hole in the shaft.

mark if i've got the jist of your post if i try a test bend and let it cool natrulay how could i test its strength? whack it with a hammer?

 

[mark sanger]

H

Jason

There ya go I should have paid more attention. Straw colour that was the bit I forgot about.

Sorry george. didn;t mean to mislead.

Now where are those books I had.

Take care

mark

 

[cornucopia]

You need a high carbon steel to be able to harden & temper it. As luck wood have it "drill rod" is the American term for "silver steel" which is easily available in the UK.

Case hardening of a low carbon steel rod will be a waste of time as after the first regrind the hardened surface will be removed

With the silver steel just heat the working end to cherry red and quench, this will harden the metal but it will be brittle so needs to be tempered. Clean back to bright metal and heat to a med/dark straw colour then quench.

Jason

just what i needed to know thanks- david ellsworth lets his cool naturally and his are fine so thats what i'll do with the silver steel.
thanks

 

[jasonB]

As its just the shank, then silver steel makes little difference. Assuming its going to be a tightish bend in 10-12mm dia rod then it may be easiest to bend while cherry red then just allow to cool naturally.

I've made inserted tools with 12mm stainless shanks as I had some laying about.

Jason

 

[cornucopia]

yes sit will be a tight-ish bend in 13mm rod.
thanks again for your help

 

[mark sanger]

Well you could whack it with a hammer.

No after you have made it soft ( no this is depending if you actually need to soften it to bend it) you probably will have to as if it bends that easily it will not stand up to cutting forces.

You then need to return it to the state in which it was before you made it soft.

So as Jason clarified you need to heat it up to straw colour (the bit I forgot, thanks Jason) and then plunge into oil.

Then the main body/tool will be strong again without being brittle.

Now is the time to whack it with a hammer without the availability of proper metal testing facilities which is getting a bit space age for what you are trying to do. Izod testing and all that malarky.

I doubt that you would make any metal brittle enough to become dangerous to use especially when cutting wood.

If I was making it I would put the main shaft in a vice and try to bend it. If it flexes then it won't snap.
Then I would be happy to use it. But that is just me.

Hope this helps

Mark

 

[jasonB]

You then need to return it to the state in which it was before you made it soft.

So as Jason clarified you need to heat it up to straw colour (the bit I forgot, thanks Jason) and then plunge into oil.

No, this is tempering, which is done after hardening, neither of which will be required for a shaft that is not doing any cutting. The hardening & tempering advice was given before I knew it was a separate cutting tip.

As said, assuming you need a tight bend in 10-12mm material then you will have to do this while the matal is red hot. Once bent leave it to cool by itself, this will in effect anneal the steel and allow any stresses out and return it to the state it was in before you started.

Any form of quenching be it in water or oil from red hot or straw colour will harden the steel and make it brittle with the potential for the shank to snap if you get a dig in.

Jason

 

[Paul.J]

Any chance of doing another pictorial George when you do this :?:

 

[cornucopia]

Any chance of doing another pictorial George when you do this :?:

okey dokey paul- the metal is on order from chronos- hopefully it will be deliverd in the next few days.

 

[mark sanger]

George

Apologies if I confused the issue. Not meant to and out of good intent. But it obviously has been too long. Should learn to keep quiet. Once you have done it let me know how to do it properly. lol :?

Take care

Mark

 

[Paul.J]

Nice one George.
I will look forward to seeing them.
It should also give a better idea of what has to be done.