I have aquired a dozen large ball bearings (3") from a crane base. I have heard that they would make a good knife, any thoughts on this. Thank you. Mike.

I think 3" bearing could have lots of great uses to the extent that it would be kind of a waste to use them for knives. Good steel, so I've heard, but you would have a heck of a lot of forging to get a knife, a heck of a lot, as compared to forging a file into a knife.

There could be other considerations though.

look it up but alot of ball bearings and race are 52100 hard to work but strong.

It is best to anneal ball bearings prior to forging. Heat to a bright read heat then put them in a bucket of ashes or vermiculite to cool over night. I hear lime works good also. They can shatter when your forge them if you don't anneal them first.

For a 3 inch ball bearing you better have a power hammer or a strong arm. I have some 2 inch tall 2 inch diameter roller bearings and it takes one heck of a lot of pounding to get them into a bar for knives by hand. Also 52100 is difficult to work with, it is easy to stress crack it by hammering it too cold.

Some bearing races are 52100 also but some are case hardened mild steel. Easiest way to check is to grind a spot with a belt sander or angle grinder then try to file that spot. If it is case hardened you will be able to cut the spot easily with a file because the hardened area has been ground away.

If they do end up being 52100 steel it will make a great high performance knife if given the proper thermal cycles and heat treat, Ed Fowler swears by the stuff. Ive heard the key is low temp forging followed by a triple quench at heat treat, its worth looking into

I am the machine shop supervisor in a factory that makes roller bearings. Really big ones. Most of our races and rollers are made of 52100. These are typically through hardened. Many, if not all, of our tapered bearings are made of 3310 and 4320, and case hardened to a depth of around .100".

I have a pretty limitless supply of 52100 scrap, and can attest to the fact that it is difficult to work with. You will want to anneal any rollers or balls that you have scavenged.

YOU can buy 52100 steel from some of the knife material suppliers in shapes and sizes suitable for making knives. Why spend the extra time beating on a large ball or roller bearing..Three inches diameter would be a challenge size wise for my 50# little giant. Before I could beat it into a bar I could take a new piece of bar stock and have it forged or ground and into the heat treating process .

Thanks guys, I really appreciate the input. This is a great web site! Mike.

Friend told me you need to knick the outside of the ball bearing through the outer shiny surface, he had one explode when he was heating it to anneal, don't know myself as I havn't found any yet

are you sure it wasn't a cannon ball, both are round but there the similarity ends

Never heard of nicking the surface, what is that supposed to do?

I am new to knife making. I see a video of a guy putting ball bearings in a looks like some kind of a plaster cone to melt the bearings. Does anyone know what that was and made of ?

Welcome aboard Bigjc, glad to have you. If you'll put your general location in the header you'll have a better chance of hooking up with members living within visiting distance. 

What you usually see in online videos is mostly made of BS. I don't know of any legitimate bladesmith that melts steel  to make blades. That is NOT to be confused with the fellows who collect ore and smelt it in a bloomery, that is an entirely different process.

The main lesson to take away here is to take ANYTHING you watch online with a lot of salt. There are some excellent how to videos online but if you don't know enough to filter out the good from the bad you'll only be slowing your progress.

Stick with us, we'll steer you straight, we have a number of world class and famous bladesmiths on the forum. There is an extensive section on Iforgeiron, it's in the table of contents. 

Do some reading until you start to get a handle on the terminology and what's what so you can ask good questions without having to explain what you meant when you used an uncommon word. 

Frosty The Lucky.

Melting 52100 would probably mess up it's chemistry and crystal structure and result in a poorer  blade than if you had just forged out a ball bearing.