Heat blues springs

[Kevin Houlihan]

I typically polish and heat blue screws on my rifles. If I polish a frizzen spring on a completed working lock and then heat blue it to a brite blue will the temper get messed up?
Kevin

[WadePatton]

Color means heat, and heat changes steel at certain points. Here is one of the best references i've seen on the tempering end of the scale.  No i'm not heating a spring unless I'm trying to change it.  But don't take my word for it. MANY others have a better working knowledge of this.  All steel is alloy-it generally helps to know which one, as they exist because of their differences.

[jerrywh]

 Heat blue will not hurt springs. It may even improve them some. Springs temper far above the heat blue temp required.  Heat blue from 565° to 650°.    V Springs temper from 725° to 800°

[D. Taylor Sapergia]

That's really interesting Jerry.  All these years I've been taking springs to or at least aiming at the 590 colour.  It's amazing what you can learn when you pay attention.  Thanks for the tip.

[Kevin Houlihan]

Thanks for the responses. On a polished lock brite blue screws look nice and I was thinking that the frizzen spring would look nice the same bright blue color.  I'm going to try and heat blue a spring.  At least if I mess one up I can blame you guys
Kevin

[David Rase]

Thanks for the responses. On a polished lock brite blue screws look nice and I was thinking that the frizzen spring would look nice the same bright blue color.  I'm going to try and heat blue a spring.  At least if I mess one up I can blame you guys
Kevin

Clamp a piece of bar stock, 1/8" x 1 " x 1' long, or what ever you have that is close, in the jaws of your vise.  Only clamp about 4" in the vise jaws leaving the rest hanging out.  Place the spring on the bar stock and heat the bar stock from underneath with your torch.  I use propane for this operation.  Heating the bar stock up and letting the heat transfer to the spring is way more controllable then heating the spring directly with a flame.  Play the flame back and forth pulling it away periodically and watch for the spring to turn color.  Stop short of the color you want as the spring will continue to absorb heat from the bar.  This low tech method will work fine for what your want.  You might even try a test piece first to gain some control in applying the heat evenly.
David 

[Jim Kibler]

It's not just temperature, but the proper temperature for a given alloy.  It's better to consider desired hardness and consider an appropriate tempering temperature to achieve this.  For materials such as O1 temperatures well in excess of 900 F are necessary.

[Scota4570]

For springs I use a lead bath to temper with a thermometer. 

I use the same rig to cast bullets.   

[Tony Clark]

Color means heat, and heat changes steel at certain points. Here is one of the best references i've seen on the tempering end of the scale.  No i'm not heating a spring unless I'm trying to change it.  But don't take my word for it. MANY others have a better working knowledge of this.  All steel is alloy-it generally helps to know which one, as they exist because of their differences.

That is a great chart but it should be labeled "how to judge the temperature of steel by it's color when heated" because you can use those colors to harden or soften a piece of steel...tempering is softening...as far as tempering a spring (softening a fully hardened spring to the correct "springiness" )  goes like Jim explains the temperature would vary slightly depending on the specific alloy. Taylor... whatever you have been doing all these years must be correct as I doubt you been breaking many springs huh? If you would have you'ld have been taking them a little farther already I would think?
Regardless... you won't hurt any properly hardened spring made of suitable material by bringing it to a bright blue.....
the riddle of steel is so wonderful... sometimes things are best learned by having the test 1st and then the lessons.

[jerrywh]

 The only problem with tempering by color is this.  The temperature when tempering must be held for a certain length of time.  Always think of tempering as cooking a bisque. If you don't hold the temperature long enough the spring or whatever it is will not be done on the inside. A good rule of thumb is to hold the temp. 12.5 minutes for each 1/8" of thickness the part is thick. I always hold gun springs at 725° to 750° for 20 minutes. Do this and you will have very few failures. Most other failures are caused by flawed steel or forging incorrectly. 

[Bob Roller]

The only problem with tempering by color is this.  The temperature when tempering must be held for a certain length of time.  Always think of tempering as cooking a bisque. If you don't hold the temperature long enough the spring or whatever it is will not be done on the inside. A good rule of thumb is to hold the temp. 12.5 minutes for each 1/8" of thickness the part is thick. I always hold gun springs at 725° to 750° for 20 minutes. Do this and you will have very few failures. Most other failures are caused by flawed steel or forging incorrectly. 

I have used the color method of tempering springs,sears and tumblers for decades and
have replaced ONE mainspring in the last 40+years.I learned this method from an old
gunsmith here in Huntington WV,George W,Killen.Bill Large also used this method with
no problems.I read about these various methods using whatever like melted lead etc.
but I cast bullets when I melt lead.

Bob Roller

[rich pierce]

The only problem with tempering by color is this.  The temperature when tempering must be held for a certain length of time.  Always think of tempering as cooking a bisque. If you don't hold the temperature long enough the spring or whatever it is will not be done on the inside. A good rule of thumb is to hold the temp. 12.5 minutes for each 1/8" of thickness the part is thick. I always hold gun springs at 725° to 750° for 20 minutes. Do this and you will have very few failures. Most other failures are caused by flawed steel or forging incorrectly. 

Wow that's a long hold at tempering temp- I've never done this and so that might explain that failure I had.  Thanks for the info Jerry.

[James Wilson Everett]

Guys,
Yes, right, I do agree with jerrywh.  Instead of holding the temper heat for 20 minutes, I bring the spring to the temper heat I have selected several times.  That is, bring the spring to the 810F temp, then let it furnace cool down to around 750 or so, bring it back up to 810F, repeat.  Probably gives the same benefit as the 20 minutes jerrywh uses.  Anyway, it works for me.  Oh yes, this is for AISI 1095 steel, brine quench.  The 810F temper heat is well above the blue color range, so to polish the spring and reheat to get the pretty color does not alter the metal properties.  I do this on occasion, but I try for the color I call "peacock" - sort of a blue-purple-brown mix, (looks like just between the 500F - 540F samples shown) another guy on this site calls it "possum ear" - a great name, for sure.

Happy New Year to my friends,

Jim

[Bob Roller]

Guys,
Yes, right, I do agree with jerrywh.  Instead of holding the temper heat for 20 minutes, I bring the spring to the temper heat I have selected several times.  That is, bring the spring to the 810F temp, then let it furnace cool down to around 750 or so, bring it back up to 810F, repeat.  Probably gives the same benefit as the 20 minutes jerrywh uses.  Anyway, it works for me.  Oh yes, this is for AISI 1095 steel, brine quench.  The 810F temper heat is well above the blue color range, so to polish the spring and reheat to get the pretty color does not alter the metal properties.  I do this on occasion, but I try for the color I call "peacock" - sort of a blue-purple-brown mix, (looks like just between the 500F - 540F samples shown) another guy on this site calls it "possum ear" - a great name, for sure.

Happy New Year to my friends,


 BRINE quench?? I use that to harden a frizzen unless it's 52-100 which seems to work
best when oil quenched.I base this on personal experience and the lack of returned locks and triggers.

Bob Roller

Jim

[Long John]

Thanks for the discussion!!

This is one string I have printed out and put in my notebook!

I have always used boiling oil for my spring heat treat.  SAE 10 oil has a well-documented boiling temperature (see the MSDS) and boiling temperature is only dependent upon altitude and the chemical content of the oil.  I put the part in a steel can filled with oil and play the torch on the bottom until the oil in the pot boils.  The temperature cannot exceed the boiling point for that oil and the temperature is easy to maintain long enough to get a good soak into the steel and end up with uniform temperature through the spring.  But I think I might have to select a different weight and possibly type of oil to achieve the temperatures that Jerry is recommending.

Thanks again.

John Cholin

[jerrywh]

Long John.
  

When I was in my mid twenties I made many dozens of gun springs for gunsmiths and restorers around Portland Oregon including the Oregon Historical society museum curator.  
  I know a lot of old time gun smiths that used the burning oil method as I myself did years ago and it does work usually. The old smiths used mostly linseed oil and it has a fairly high flash point. They also used animal fat which probably doesn't.  I have put a lot of thought into why it does and rarely doesn't.
  This is what I have concluded.  When the oil burns it is a fact that the oil does not exceed the flash point temp of the oil being used however, The flame above the oil is about 1500°. As long as the spring is covered with oil it will not get any hotter than the oil. that temp with linseed oil is about 675°.  The flash point of linseed oil is below that but the auto ignition point is 675°  according to the safety data sheet.  As the oil burns off part of the spring is exposed to the flame and the spring temp will rise above the temp of the oil but not much because the oil tends to keep it cool. As the oil burns of the spring gets hotter and hotter but at some point it begins to decline again because the flame declines also.
  the end result is that the process usually always works but is messy. lt never failed for me as long as I left the spring in the oil till it was all burned off.  Let me say this. One cannot assume that .  it was tempered wrong even if the spring breaks. If I make a spring from scratch now I always test the steel by the heat method before I forge it. A lot of factory spring steel has rolling flaws in it.  I heat the steel to about 1500° and look at it closely, If there is a rolling flaw in it or a crack you can see a bright line in the steel where the flaw is. A crack will show as a bright line or even a rolling flaw.
     I been working with this stuff for about 60 years now. I hope I can help somebody from going through the problems I had.  I wish I knew Bob Roller personally. He is a treasure trove of info.    
 Pure lead melts at 625° bit it is always hotter when casting bullets. So it works pretty good also.

[FDR]

I wonder if early smiths were familiar with "Nitre" blue?  They had black powder and saltpeter was a commonly used item especially in curing meat.

[Tony Clark]

 BRINE quench?? I use that to harden a frizzen unless it's 52-100 which seems to work
best when oil quenched.I base this on personal experience and the lack of returned locks and triggers.

Bob Roller

Well Bob I totally agree you would never use a brine quench that is far to harsh for a spring from a modern made lock and unnecessary even foolish. You can heat treat using temper colors and soak it if you know what you are doing. Some experimentation is the best lesson in this case I believe and the results become obvious soon enough. That is what smiths did in the past when they didn't have thermometers or ovens to do the work that experience teaches you when that is all you had to do the work. Jerry , your work is above and beyond what past gunsmiths did or were able to do... perfect for sure.

[Bob Roller]

 BRINE quench?? I use that to harden a frizzen unless it's 52-100 which seems to work
best when oil quenched.I base this on personal experience and the lack of returned locks and triggers.

Bob Roller

Well Bob I totally agree you would never use a brine quench that is far to harsh for a spring from a modern made lock and unnecessary even foolish. You can heat treat using temper colors and soak it if you know what you are doing. Some experimentation is the best lesson in this case I believe and the results become obvious soon enough. That is what smiths did in the past when they didn't have thermometers or ovens to do the work that experience teaches you when that is all you had to do the work. Jerry , your work is above and beyond what past gunsmiths did or were able to do... perfect for sure.

I use no ovens or thermometers and rely on years of experience to do what I do.
My record is what it is.I am winding down now and MIGHT make three or four locks a
month and maybe not. Right now I am taking no new orders.
Earlier I said I had replaced one mainspring in one of my locks. It had been altered
by someone and the color was all messed up.

Bob Roller

[sweed]

Thankye Thankye Thankye...... What an education....Years of experience to experiment with!!!!! Would not even try this with out this education!!!

[Dphariss]

That's really interesting Jerry.  All these years I've been taking springs to or at least aiming at the 590 colour.  It's amazing what you can learn when you pay attention.  Thanks for the tip.

Me too. Almost never break one.
Use molten saltpeter.
Dan

[Dphariss]

I quit water quenching frizzens when I cracked an engraved one.
So I use oil, warmed Marvel Mystery oil works good but mine has some heavier oil in it too. Warming the oil to 100-120 will greatly improve its cooling properties.
I caseharden all screw head and usually the threads too then polish and draw back to bright blue. Casehardened screws sometimes chip at the edge of the slot if not tempered. Wirh engraved screws done by someone a couple hundred miles away its best not to chip or BURR the screw slot.
I oil quench springs regardless of material. Then polish, degrease and take to bright blue in molten saltpeter. Good enough that I have no reason to change.

Dan

[jerrywh]

 Potassium nitrate or salt peter works well for tempering and fairly well for heat bluing. However I now use sodium nitrate for some heat bluing.  Sodium nitrate melts at about 546° instead of 620° The lower melting  temp permits me to have a little more time to watch the colors change. Too rapid of a color change can make it hard to stop at the desired color.  The niter bluing salts that Brownel  sells is Sodium nitrate. There is a mixture of the two that will melt even lower. 

[Dphariss]

I have a life time supply, I think, of saltpeter.
The Madis book on the Winchester has a description of how Winchester used Potassium Nitrate, well "Nitre", in a cast iron container lined with polished brass (to prevent degrading the cast iron), to blue barrels adding 1/10 to 1/20th by weight of "peroxide of manganese"  But they also used rust blue, charcoal blue, or heat blued in a sand bath. The nitre blued parts were coated with oil and then baked to smoke off the oil and darken the blue. I have used this on small parts and it does produce a blue more like caustic salts blue and durability is supposed to be enhanced as well.

Dan

[satwel]

Me too. Almost never break one.
Use molten saltpeter.
Dan
[/quote]

What kind of equipment is required to melt saltpeter? Is it difficult and/or dangerous?

Thanks