Spring Tempering Methods

[Cpl. Ashencheeks]

I am going to try my hand at making a flat main spring.

I ordered a pre-annealed 1075 flat stock kit and am curious when I get it shaped and polished for final fitting how to go about tempering it.

The reason I purchased the 1075 instead of the 1095 spring steel which is supposed to be superior, is that I have read 1075 spring steel is more forgiving towards beginners.

So I figure the process of pre-annealed spring steel goes in order of cut, shape, grind, file, polish, fire to a red glow then quench to harden, re-polish carefully, and the final step is to temper to somewhere around a blue color.

If I do not have any of that right, go ahead and correct any errors.

On the final temper step there are two methods that appeal to me in their simplicity, but I am not too sure of how the results might be.

One was to place the spring in a small shallow pan of motor oil and cook and burn away the oil completely without firing directly on the spring.

The other was to dip the spring in a lead pot to somewhere about 600 degrees Fahrenheit.

I still have to wait for my spring stock to arrive, but yesterday I decided to practice making a small light spring using a small sized worn out hacksaw blade and tempering with a vegetable based oil.

It worked to some extent but the spring made with the hacksaw blade is probably best suited to very light applications such as a ramrod tension spring.

Any corrections, suggestions or tips will be greatly appreciated.

Thanks for reading this.

 

[chawbeef]

I'm looking forward to the answers you get on this subject. A learning curve for sure :thumbsup: ........Daniel

 

[dave_person]

Hi,
I use 1075 steel for springs all the time. In fact, I usually replace all mainsprings on Davis and L&R locks with my own. To harden the steel, heat it to bright red and quench in canola oil. Then clean up the spring and polish it a bit and heat it to 750 degrees. The color is a light blue beyond the bright darker blues of lower temps. However, to temper a spring correctly that heat must be maintained for about an hour and then the spring is let cool slowly. If you immerse the spring in a small quantity of motor oil and set that oil on fire with a torch, it will create and hold a temp of about 750-800 degrees for however long the oil burns. That method works but is somewhat hit or miss and often results in really spongy weak springs unless the spring is really thick and big. You can melt lead and immerse the spring in the lead bath, which approaches about 600-650 degrees and that may work but you will break a few. The best option is a heat treating oven that can be controlled at a specific temperature of 750 degrees. With regard to shaping the spring, you have to specify what kind of lock it is for otherwise the question is meaningless.

dave

 

[Cpl. Ashencheeks]

Thanks for the answers.

This would be a mildly curved main spring for a matchlock sear spring.

I tried a few different options of already made re-purposed springs like a frizzen spring, but it did not work out as well as I would have hoped. There just was not quite enough play on the spring to use effectively.

So I started the lock over again with a fresh lock plate which has yet to be drilled for the sear pivot, serpentine and other connecting screws.

I will also be wanting to do a more traditional period correct sear and spring found in photographs of historical locks from the 17th century, about 1625-1650.

These springs usually do have too many hard bends in them except maybe at the ending contact surface areas from what I can see in many photo samples.

I have not done a full lock inlet of the stock yet, just the plate is inlet, so my options are still open as to how the lock will fit in.

 

[kansas_volunteer]

If you have an electric range in the kitchen you can draw temper, depending on the correct heat, by laying the object on the burner surface and adjusting temp. Never tried it with a spring, nor a very large object, but it could be one option.

 

[Bo T]

Dave,
Do you preheat your canola oil, or is a spring so small that it doesn't make a difference?

 

[Vaino]

I harden and temper springs once in awhile as needed and my method is probably quite crude, but the springs work well.

I use 1095 spring steel and form the spring and ensure that there aren't grooves or notches in the spring, especially on the edges. The spring is polished on all surfaces.

The spring is heated to a red/orange color and dunked in what I think is old motor oil. It's then polished on all surfaces. I made a small enclosure out of a larger dia. pipe w/ an end cap that has some holes drilled through. The spring is wired and is heated in the pipe ...a very uniform color is achieved.

A 1/4" thick steel plate clamped in a vise is heated w/ a Mapp Gas torch from the bottom side and the individual spring surfaces are laid on the plate one at a time until all the surfaces show a gray blue color. Special attention is paid to the bends by "rocking" the bends on the hot plate. The same can of old motor oil is kept handy for dunking the spring when the gray blue color is going to be achieved too soon. .

The tempering isn't rushed and a spring made from 1/16" thick stock takes approx. 30 mins to complete and the plate is heated periodically. Heating the plate is the only facet that takes a little guessing as to the plate temp...although a slightly lower plate temp is always better so the color takes longer to achieve. The heating of the plate gets easier after a few springs.

When I was in the toolroom and some sort of straight or leaf spring broke on a production machine or its tooling, time was of the essence and the above method was used for a newly made spring. Didn't encounter any failures w/ these springs.....Fred

 

[dave_person]

Hi,
Does your electric oven reach 650 or higher degrees?

dave

 

[dave_person]

Hi,
No, the oil is at room temp. SAE 1075 and 1095 steels should be cooled quickly.

dave

 

[LRB]

Very good advisory. A lead bath at 750° would be a good way to go, if you have a lead pot with controls that can be trusted. I would suggest heating the canola oil to maybe 130°, give or take a tad. The heated oil cools the steel faster than room temp oil. Heated oil has a lower viscosity than cool or room temp oil, and also allows for a more even cooling which reduces the chances of cracking.

 

[Larry Akers]

It has been suggested to heat the spring to various colors of red for quenching. Judging color is subjective at best so I heat springs to the point that a magnet is no longer attracted to the steel, then quench in warmed (130F) canola oil. Tempering is done in a lead pot at 800F with the spring wrapped in aluminum foil. The spring is held in the pot for a minimum of an hour.

 

[LRB]

Actually, you should heat to the next shade, or even two shades of red hotter than non-magnetic. Loss of magnetism happens at 1414°, which is at least 60° less than ideal. Your target heat should be at about 1475°, to a tad more with some steels, but not much less. You can learn to judge the proper color of red heat by using common table salt as a guide. It melts at 1474°. However, you may certainly do as you think best.

 

[dave_person]

Hi Wick,
I didn't realize table salt melted at 1474. Do you reckon that it might be a good material with which to check the calibration of the oven?

dave

 

[LRB]

It should be. I think I would use plain non-iodized salt though.

 

[rich pierce]

The lead bath works best for me because it's easier to get a good long soak when tempering.

 

[LRB]

As long as you are sure that the temp is reasonably close to what you want, it is a good way to go. It used to be a fairly common practice years back, but lead phobia has made it uncommon today in most industry. Probably a good thing overall, but the fear of lead can also go too far in many cases.

 

[M. De Land]

Good advise. I can't think of anything to add.
I like to use the new oven I have as it is very precise and Dave is right about soak time for annealing.
I like and have used the 50-50 motor oil cut with turpintine,cover over the spring on it's side , light and let burn out, with good success but the books say to use 1 hour at a prescribed heat for the best hardening and quenching.
I draw all my color cased receivers for an hour to prevent cracking.
Coil springs are just wound cold on a mandrel in a lathe using spring wire from Hobby Craft and they work perfectly with no heat treating.

 

[ohio ramrod]

I have had good results with the "lead bath" for tempering springs. I leave them in for 20 minutes remove and place in lime overnight. :idunno: :idunno:

 

[LRB]

Why do you place them in lime?

 

[Zonie]

Maybe that's the excuse he uses when his wife finds 4 or 5 juiced limes laying on the counter top?

As ramrod is sipping on his Margarita out in the gun room he says: "Oh. Sorry dear. I'm just tempering some new springs with lime."

:grin: :rotf: