View Full Version : Hardening O-1

10-22-2007, 12:03 AM
I've made a little pin for the collet closer on my lathe that I think should be hardened. It drops into a ring with 24 holes that have definitely been hardened and you shoulda seen how worn and mangled the soft pin I found in it was ....

So I made the new pin outa O-1 hoping to at least improve upon what was in there. It's 2" long with a .150 dia on either side of a .250 flange. Not big.

I've been in the oracle of all things machine, namely the Handbook, and think I understand the process but have no means of accurately determining if I'm anywhere near 1400 degrees. Being O-1 I know I'm supposed to use oil for quenching and tempering, but haven't a clue what kind might be suitable. And then there's the whole issue of scale.

Not needing perfection but wanting to do a decent job on this, is there some kind of rudimentary process the homeshop guy can use?

Thanx for any tips.


J Tiers
10-22-2007, 12:27 AM
Heat with torch to approximate proper point, dunk in oil. Pull out, polish up, then heat to 'color hardness".

"Plain" oil is probably best, without any junk in it, i.e. not motor oil.

I understand that thin oil is best, as it flows and removes heat at the rate expected. But the main deal is that the heat is removed somewhat slower than with water, which sucks out heat very fast due to its very high thermal capacity.

I've used the kitchen stove (good for larger items that conform to the shape of the burner) a propane torch, a rosebud..... but not a furnace. obviously with a good furnace and temperature controller, you can optimize the process.

For tempering, I watch the colors. As usual, a furnace would be best, but I don't have one. If the part is small, a small metal plate is good to eevn out the heat.

For your pin, I'd suspect a low hardness, between straw and blue, would be best, as you don't want it to shatter.

A.K. Boomer
10-22-2007, 12:44 AM
Iv had good luck with items that size of O1 and just using a propane torch, Use cutting fluid because it has sulfer in it which is what you want, I get it glowing good and try really hard to dunk it uniform, i think its important to avoid warping of the piece, if the peice is flat dunk it edge in and fast, dont favor a flat side or it will go crazy,,,,, I would put a pin in direct and fast -- not to any side...

Water is terrible not just for the quick cool but actually quite the opposite sometimes, its sets up a vapor barrier --- some of the part may cool to quickly and some may keep a vapor "shield" around it long after, then the shield collapes and its instant trauma...

Im bad about one thing --- I usually dont re-heat to a lesser temp and then let cool -- i dont know why but i get scared:o it seems the parts iv used work good and I dont want to fuqe with that..

10-22-2007, 12:47 AM
Like Jerry said,only I use a magnet at dull red,once a magnet will no longer grab the pin it's ready.

Other than that,on long slender parts make sure you dunk the part held vertical,lying sideways it will warp since one side will cool faster than the other.

10-22-2007, 03:52 AM
I'd be real careful using a hardened pin in a situation like that.
The pin is designed to wear.
It's a damn sight easier to make a new pin than try to tackle worn holes.
If you do harden, make sure it's tempered well back, so it's still softer than the ring.

10-22-2007, 07:37 AM
Thanx for the tips guys. I got a magnet and a refractory brick to roll it around on while heating with propane. My bro works at McMaster and I just realized they sell quenching oil in 2 different flavors. 28 or 11 second. 28 sounds like it'd be less likely to mess up on a first attempt.

And I hadn't thought about a longitudinal dip but yeah, that'll be less likely to warp out on me. Gonna do that.

For tempering I was thinking to heat a pan of the same oil on a camp stove or something. I can measure up to 500 degrees with an infared pyrometer from tire temp days so I got some control there. That should cool slowly enough to get some ductility back.

I don't believe the pin I found in there was from the original design BTW. It was bent for one reason and the engaging end had a notch worn in it where it was barely engaging on half the dia. Best guess is it was shopmade of ordinary steel. With one pin and 24 holes to go in it stands to reason the pin's gonna see 24 times the wear. Dead soft wouldn't last long at all and in fact it didn't.


10-22-2007, 08:09 AM
I'd be real careful using a hardened pin in a situation like that.
The pin is designed to wear.
It's a damn sight easier to make a new pin than try to tackle worn holes.
If you do harden, make sure it's tempered well back, so it's still softer than the ring.

kind of what i thought reading the question, drill rod, even unhardened will be tougher than mild steel and might be the way to go

10-22-2007, 08:16 AM
I think for tempering you should do as J Tiers suggested, and reheat the pin with a torch. After polishing you will be able to see the temperature that you desire quite easily.
Here is a chart to guide you in determining the temp you are after.


Heating the oil to the temps you are after could get kind of smelly if not dangerous because of the fire hazard.

J Tiers
10-22-2007, 08:18 AM
I think the "seconds" you mention are "seconds Saybolt" and if so, they are a viscosity measurement.

The thicker oil will likely have a different effect, but that "seconds" is NOT anything to do with the length of time to harden, if that is what you were considering.

Water is a very violent quench. If you add salt or lye to it, it lies quieter, without boiling as much, and is even MORE violent. To keep it from boiling, you move the part or the water fast.

What you get is a hard exterior, and soft inside.

Oil hardening steels don't need as violent and fast a quench, and as a result oil carries enough heat to do the job. Those steels also harden deeper.

Air hardening even more so

Forrest Addy
10-22-2007, 08:24 AM
Small items like yours will cool quickly enough to air harden. Heat and cool in an air blast. I suggest this only in the interests of avoiding mess. Further you need to harden the wearing part not the whole thing. If the part is round and long enough you can grasp it is a drill shuck and spin it while you heat it then cool it with compressed air. Then while its in the drill polish and draw to color.

The part will not get to full hardness but then you don't need it to. About spring temper is right for a shot pin on an indexer. Leave a little stock on the fitted portion. Heat treating will make scale. A little stoning under power in the lathe will remove the scale and reduce the part to size.

Al Messer
10-22-2007, 09:17 AM
Heat it up to Cherry Red heat with the torch and dunk it in some 30 wt. Motor Oil at room temperature.

Your Old Dog
10-22-2007, 09:22 AM
I've had good luck using pennsylvania parafin base 10 wt non-detergent motor oil.

I put it in a small soup can filled with oil. I sink the part straight into the middle of the can and rest the plyers on the side of the can so as to hold the part steady. If you swirl it you loose it's ability to self-temper. The hot oil forms a warm jacket around the part that will anneal it to some degree. It works for fire arm springs and it works for engravng chisels if of S-5 steel.

10-22-2007, 10:01 AM
A simple rule to hardening is that unalloyed steels with medium to high carbon content such as 1040 are water quench steels. The higher carbon types are air hardening. The general term for these steels is carbon steels.

Alloyed steels (containing significant percentages of other metals) are generally oil or even hot lead quench steels, examples being 4130, 4140 etc.

For those new to the steel alloy designation system it is worthwhile to learn what the numbers of the alloys mean. They aren't just random numbers but contain important basic information about the steel that can be used to determine such things as how to harden the alloy or if it even can be heat treated.

Basic metallurgy is something every machinist needs to know. Everything about steel can be found at this link with nearly all the articles free with no subscription or registration.


10-22-2007, 07:59 PM
great link Evan, very interesting!

10-23-2007, 04:45 AM
Forrest's method was so simple and easy I gave that a shot. Not sure how hard I got the tip but it's definitely still softer than the ring. I smacked 'em both some with a punch and I can leave a mark on the pin with relative ease.

I'll run it and see what happens. Easy to make another and continue my education if it doesn't work out.

Thanx again guys.