Spring tempering using burning oil

[sydney]

 I don t make a lot of springs but when I do I use the burning oil method
   Does any else use this method and if so how are you doing it ??
    How are your results ??
    Sydney

[D. Taylor Sapergia]

I've only used that method once Sydney.  And it worked well - made a god spring.

I used a sardine tin, placed the spring into it, and covered the spring with new motor oil.  I used a propane torch to ignite the oil, and it took a while to make it flash.  It seems that the whole can of oil has to come close to ignition temperature to flash into a flame.  And it was a long time before all of the oil burned off.  I did it outside.  As I said, it resulted in a good temper.

[Thom]

This is my usual method. I rip an aluminum can in two and pound the bottom flat. I think Kitt Ravenshear said use one teaspoon of oil. Perhaps a bit more for a spring the size of a mainspring. The proper amount of oil should burn off in a flash. Using too much oil will result in a smoking spitting mess of flame, but as Taylor said, you still get a good spring.

I use a propane torch with motor oil. I have also used sperm whale oil.

I know there are more sophisticated methods of tempering, but I'm not very sophisticated. If it didn't work for me, I would find a new method.

Thom

[David R. Pennington]

 I have done it this way and made some good springs. I sometimes err on the side of caution and use too much oil. Then the spring is a bit soft and have to do it over but this is better than too hard and a broken spring. My mainspring in my .40 I got too soft and it relaxed on me a little. I need to do it again. I might just go by color this time.

[thimble rig]

I use this method for making springs for my patchboxes.It works pretty well.I use a little can that mints come in.And I use some old hack saw blades for my springs.

[jerrywh]

 I am aware that this is a controversial subject . I am only offering the information that I have accumulated over the years. I have done this before using motor oil , and animal oil or lard. It worked well both times. This process satisfies the time factor as well as the temperature factor. I prefer the lead bath because it is less of a mess and there is no open flame to worry about.

The flash point of oil is the lowest temperature at which the VAPOR of oil will ignite.
The Flame point or auto ignition point is the temperature at which the oil will self-ignite and keep burning after the heat source is removed.  The boiling point of oil and the flame point are the same.
 The temperature of the flame is much higher than that of the oil and the flame temperature of all petroleum base oils are near equal.
The temperature of the oil itself will not exceed the flame point. The same as water will not exceed the temperature of the boiling point when boiled because any water of oil above that temp is carried away as vapor.  I am assuming that if it is true with water it is also true with any boiling liquid. Correct me if I am wrong.  See data below.

The Flame temp. is the temp of the flame produced by the burning oil.

raw- linseed   auto ignition =     631°F
Canola oil auto ignition point      795°F
petroleum      auto ignition        752°
vegetable oil     auto ign.          762°
Olive oil         auto ing.             816
Smart ballance°    auto ign.       809°

Flame temperature        °C             °F
Kerosene    Air            2093          3801
Light fuel oil Air            2104          3820
Medium fuel oil Air    2101          3815
Heavy fuel oil Air            2100          3817
Based on these facts I would select a petroleum based oil and fill a small container with enough oil to completely cover the spring and more. I would place the spring in the oil and heat from underneath until the oil self- ignited and discontinue heating.  Then let it burn until the spring was exposed and then put a lid on the container letting it self- cool. I would not do this in my shop. Although I have. That’s why I wouldn’t do it again.  If the oil goes out when the heat is removed it is not hot enough.  There is a bigger danger of over heating the spring than under heating it. That would not be a big problem. As you can see the flame is much hotter than the oil so too much exposure to the flame could result in the spring ending up softer than you like. If I remember correctly Jim Chambers tempers his springs at 800° I do mine at 725°.  In operation I can’t tell any difference between the two. Kerosene lowers the temp. of all the oils considerably.
 The flame or auto ignition point of Kerosene is a mere 428°F

[Captchee]

 I also do my springs in Oil . Not much I can add that the others haven’t already said .
 The one thing  not mentioned that I possibly do different is I boil the oil before lighting it .
   I have an old propane stove that I use outside to do  springs and niter bluing .
 I place the springs in a  tin cup  cover them with oil . Bring the oil to a boil , turn the heat off  and then light it .letting the oil then burn off .

[D. Taylor Sapergia]

Jerry:  so you do not burn off all of the oil...just 'til the oil burns down to expose the spring - then extinguish.  The soak in the burning oil is enough to temper the spring.  Have I understood you correctly?

[jerrywh]

 Taylor.
   That is basically correct. I let it go slightly farther but only till the spring is a little exposed. If you note the specs., the oil temp is the correct temp for tempering provided it will keep burning after the heat is no longer applied but the flame temp is way too hot and this is why some have trouble with the spring ending up too soft. To some extent the boiling oil will keep the spring from getting too hot but if the spring is exposed to the flame too long it will be too soft. In practice a spring can be tempered to as high as 1000° and it will still work but it will be mushy and might tend to bend some when flexed.  Up to a temp of about 850 most would not notice the difference. The top part of the flame is the hot part. The lower part of the flame is mostly oil vapor and is no hotter than the oil. It is a forgiving process because the tendency is to end up on the soft side rather than the brittle side. If the spring works most people consider it a success. I like a good snappy spring with no mushy feeling.
  The heat treating experts recommend that you do not let the spring cool down to room temp, after hardening  before tempering. The cooler the spring gets after hardening the more stress it has and the more tendency to crack.

[Long John]

Thank you Jerry!

Now I know I didn't totally screw up!

I fashioned my spring from 1095 spring stock O bought at Dixons.  I figured that boiling oil would be an ideal tempering medium if I could find an oil that boiled at the right temperature.  So I went to Google and googled for the MSDSs of a range of oils.  The MSDS includes the boiling temperature.  I think I ended up with SAE 10W motor oil.  I put the oil in a steel can, dropped a wire screen in the bottom of the can to keep the part off the bottom, put my spring in and then heated the can of oil with a propane torch out in the back yard.  CAUTION:  boiling oil can boil over and catch fire when the bubbles hit the torch!

After several moments of excitement I learned how to play the torch onto the bottom of the can of oil to maintain a boil for about 10 minutes.  then I removed the torch and let the whole deal cool down to room temperature

BOING! BOING!  BOING!

Yup that spring really works!

Best Regards,

John Cholin

[D. Taylor Sapergia]

Thank you Jerry.  This all makes perfect sense.  Thanks Sydney for raising the question.

[Jim Kibler]

A reminder which has been previously mentioned.  The strength of a spring (or lack there of, "mushiness") does not depend on tempering temperature.  If too soft, the spring may not return to the original shape once flexed. 

The ideal spring is where it is as soft as it can be and still return to it's original shape.  This is the basic principle of springs for the work we do.

This may not agree with intuition or what you've heard, but it is truth. 

So as I've mentioned, pick your alloy, temper at as high a temperature as you can such that the spring returns to it's original shape.  Reference a tempering chart if you like and shoot for mid to low 40's on the HRC scale. 

Many springs are very forgiving.  Mainsprings aren't. 

Jim

[jerrywh]

http://www.cashenblades.com/steel/1095.html
 This chart shows that a temp of 725° will result in a Rockwell hardness of 45. which verifies what Jim kibler stated.

[Jim Chambers]

We temper our springs at 750 degrees and shoot for a Rockwell of 44 to 46.

[yulzari]

In my youth in England I was shown some of the ways of an old boy who was a jobbing country gunsmith (ie he would take on anything from stocking to bushing worn pins etc.)

He used to make his springs from old files, heat to  a bright orange (in his dingy workshop) and quench in water. Then they were carefully polished, edges bevelled and the edges of the bevels rounded. Finally he put them in a small metal pan with sheep tallow and heated that until it caught fire and just left it to burn out and cool. He was apprenticed to a gunsmith who learned their trade back in the 1870's. He claimed it was cheaper to finish the spring smoothly than to make another spring or two when they cracked on a stress raiser.

My 1845 mainspring broke from some really tiny corrosion pits on the outside of the V bend from 160 years of condensation in store dripping tiny amounts of moisture down the top edge of the lock. You can barely see it but can just feel it with your fingernail. Just need to adjust the hook on the new spring to stop it catching on the tip of the tumbler.