tempering knives..

[Pran]

hi.i'm new to making knives and have a few doubts about tempering knives. i've used a piece of old spring steel(5160--straightened) to make a knife.i had to anneal it to get a workable temper.now that i've gotten it to the desired shape, i'll have to increase the temper.i plan to use old motor oil for quenching.do i have to heat the oil before quenching the knife in it??

[eljefe]

HI Pran,
great to meet a fellow knife lover.
Very impressive, your annealing and tempering foray.Some books I've read do mention about warming up the oil a wee bit, while others do not-suggest you do a google search on oil quenching?
please post pics of the blade blank and whatever process you decide to undertake.
Best
Axx

[Mark]

Pran,

Welcome to the forums!

In general, you do not need to heat the oil unless the blade is very thin, such as a straight razor.

Having said that, warming the oil is almost never a bad thing and it can be of help, so go ahead and do it if you feel like it.

How are you heating your blade, with a forge or torch or something else?

If using a forge, a simple way to heat the oil is just put a thick metal bar in the fire then when hot put it in the oil for a few minutes and it will heat it adequately.

Oh, one thing I should mention- if the pot of oil you use is uncovered, it will absorb moisture and that can put little spots on your blade when you quench it. Hot oil will help separate the water from the oil to minimise this. The best thing to do is keep your oil quench covered when not using it, but I was too lazy for that. <G>

Also, when quenching keep the item a few inches off the bottom of the pot so it will not come into contact with any water that might be down there.

[Pran]

thanks for the info mark.didn't think the moisture really mattered.i'm using a coal furnace(which i built myself).will use a rod heated red hot to heat the oil.i'm having problems positioning the blower.i'm not able to heat the entire blade in one go.i've attached a picture depicting my current setup.

[Mark]

How long is the blade you are wanting to temper?

[eljefe]

Mark, What about lime quenching?
Axx

[Mark]

Also,

The moisture in the oil is mostly cosmetic, sometimes it causes these little "spots" that can take a little extra time to clean up, but it is not really harmful to the blade.

Congratulations on your forge! I think it is neat that you built it!

What do you use for an anvil?

[Mark]

Mark, What about lime quenching?
Axx

I am not completely familiar with that term, I am assuming you are talking about heating a blade up red and then putting it in powdered quicklime?

Here, that is one way of annealing, or making the steel softer so you can file or grind it.

In addition to lime (if indeed this is what you are talking about) you can also use plain wood ashes. Indeed, one traditional method to anneal steel is to put it into a wood fire and let the fire go out.

Let me know if this is what you are referring to, or something else.

Oh, this thought just occurred to me- when you quench in plain water it makes a vapor barrier of steam next to the blade, which slows down cooling. If the item needs fast cooling you can mix chemicals into the water to raise the boiling point (common additives are salt or anti-freeze, which is toxic to animals so it needs to be coverd when not in use). Maybe this is what you are referring to?

[Pran]

the blade is 6" long(legal length in india).i'm able to get only three fourths of the blade red hot at any time.do i need to use an additional blower right opposite to the the current one?
I use a small piece of a C-section girder for an anvil.
btw, the cylinder has a dia of 9.5".this would mean i can use the furnace only for tempering the completed knife.i have to run down to the blacksmith's to cut the old spring steel(3.5' long) and straighten it.

[Pran]

eljefe,
i'm posting a pic of the blade.the tang and the blade have been worked upon after the pic was taken.
i've seen the local blacksmiths here using limepaste to quench small tools like chisels.is that what you're referring to as lime quenching?

[Mark]

Pran,

Well your knife is starting to shape up, good work!

To get more heat, try to make the fire bigger, usually the problem is not going to be the airflow so you are probably OK there.

Here are some crude drawings:

The first one, if you can fill the bottom of your pipe with clay and arrange a table so you can move the fire upwards, then you can increase it in diameter to heat teh length of your blade.

The second one, if you can arrange some bricks over the top to hold the heat in you can probably get an even heat on the blade for tempering this way.

Try to arrange a fire so that the blade can be horizontal, then you can slide it back and forth to get an even heat.

[Mack The Knife]

Welcome aboard, Pran.

With Mark advising you, you are in very capable hands. However, you may also be able to pick up some information from British Blades http://www.britishblades.com/home/index.php

I wish you success because you are doing one of the things I have always wanted but keeping putting off.

Mack The Knife

[Pran]

the first diagram looks like it can solve my problem. my setup is more like the second one and i have difficulty removing the blade from the cylinder(with leather work gloves and tongs).will get back once i'm through with knife
pran

[Pran]

Welcome aboard, Pran.

With Mark advising you, you are in very capable hands. However, you may also be able to pick up some information from British Blades http://www.britishblades.com/home/index.php

I wish you success because you are doing one of the things I have always wanted but keeping putting off.

Mack The Knife

useful link.yes, mark here knows what he's talking about.

[eljefe]

Pran & Mark,
You're right about the lime quenching-I have seen a slurry of quicklime used.
usually its the oil quenching thats popular.
I'm thinking, if you cut the top and coat the inside of a 15L can of paint (cylindrical) with a 1" thick coat of clay, dry it for 48-72 hrs, line it with coal and -in effect , make it a tandoor, then use a suitable inlet for your blower (? hand driven rotary type) and use it as your furnace, might give you more depth for your blade.
What coal are you using-the charcoal or 'railway' type coke? you may get a better 'burn' and even temp with coke.
Thats a great job you have started.I'm sure you'll do well with Mark to help you on.Do keep us posted.
Best
Axx