Spring material

[doug]

      Has anyone here tried using automotive leaf springs for making mainsprings.  I recently tried twice to make a mainspring starting with a piece of a leaf spring and forging it out to thickness then hardening in water with 1/2" of oil on top followed by drawing the temper to 740 F in a lead bath.  Both springs while springy were not springy enough and broke with the hammer just past full cock. 
     Worth noting that the material does not appear to be high carbon steel but rather some sort of alloy based on the orange sparks and no bursting carbon sparks. 

cheers Doug

[heinz]

Doug, the mainsprings vary in metalurgy with manufacture and age.  I have had good success on knives with Jeep mainsprings from the 1970's but I doo not know how they would work on mainsprings.  Mainsprings are such a critical task you might want to consider ordering some carbon steel or finding a really old spring in a junk yard

[LRB]

  Buy some spring stock so you know what you are dealing with. Mystery steel often results in failures, and spring steel is cheap.

[cmac]

I would agree- buy spring stock. However I just made folding knives this winter using old files for the blade and the spring, and although these aren't put to the test a mainspring would it worked great. I was gunshy at first I had brought up the idea on a knife makers forum and a guy told me that files are typically of the same steel GM uses for leaf springs. On the same note he had told me the cheapo Taiwan and such aren't

[Dphariss]

      Has anyone here tried using automotive leaf springs for making mainsprings.  I recently tried twice to make a mainspring starting with a piece of a leaf spring and forging it out to thickness then hardening in water with 1/2" of oil on top followed by drawing the temper to 740 F in a lead bath.  Both springs while springy were not springy enough and broke with the hammer just past full cock. 
     Worth noting that the material does not appear to be high carbon steel but rather some sort of alloy based on the orange sparks and no bursting carbon sparks. 

cheers Doug

You need to realize that its possible to do things the hard way. Seems like auto springs are often made of 5160 or some such. I don't have time to look it up.
When dealing with alloys sometimes special heat treat may be needed. no sweat for GM but a PITA for us.
Order some 1075-1095 or O-1 and make a spring. If you order the flat stock in the right thickness its saves a lot of work. 

Dan

[J.D.]

Most car springs are made of something akin to 5160, which tempers to "spring hardness" at something approaching 500 degrees F.

If the spring blank is still in good shape, anneal, harden, and temper at a lower temp. However, if you want to make good mainsprings, your best bet is to by good spring steel of a known alloy. 1070-1080 is considered to be very good steel for the application of flat springs, as used in ML locks, BTW.

God bless

[DutchGramps]

When I lived and worked in Rwanda with a Chinese contractor, there was a blacksmith who forged some spring blanks for me from Toyota Landcruiser leaf springs. Superb work,  when back home I made a main spring for a Dutch M1815 musket, hardened and tempered it in water. Did not shoot that gun enough to say anything about its longevity

[Jim Kibler]

Most car springs are made of something akin to 5160, which tempers to "spring hardness" at something approaching 500 degrees F.

If the spring blank is still in good shape, anneal, harden, and temper at a lower temp. However, if you want to make good mainsprings, your best bet is to by good spring steel of a known alloy. 1070-1080 is considered to be very good steel for the application of flat springs, as used in ML locks, BTW.

God bless

Tempering 5160 at 500 F will result in a hardness somewhere in the range of 55 HRC.  Way too hard for a mainspring in my opinion.  It seems something in the range of 40-45 HRC is generally pretty good for such a spring.  Here is a link to a document written by one of our members, JC Kelly, which talks about mainspring material and heat treatment:

http://www.scribd.com/doc/39498022/Heat-Treating-for-the-Muzzle-loader-From-www-jgokey-com

A mainspring might survive using material in the range of 55 HRC, but chances are much lower than one tempered to the hardness suggested.  The idea is to heat treat to a hardness as low as possible, but not so low as to allow the spring to plastically deform (not return to the originally pre-stressed shape).  As long as the spring doesn't plastically deform, the finally hardness will not have an affect on the strength of the spring.

[greybeard]

Many years ago an old gunsmith told me that auto sprinhs were just fine for sptings but had to be model "T"   or   "A"    springs.

[rich pierce]

In my experience it's fun to make tools from recycled steel as long as they don't fail.  The best source is not auto springs but pre-1960 agricultural steel, like harrow blades.  Nomenclature varies regionally but in the northeast, after plowing we'd used a "set of disks" to break up the rough plowed ground then level the field with a "set of drags".  The "drags" had curved bent teeth about 2' long, an inch and a half wide and 5/16" thick and were commonly made of 1080.  One of those would make a lot of mainsprings.  Some folks call this farm implement a "spring tooth harrow".  Go to a farm implement dealer out in the sticks and see if they have a junk area.

[doug]

     I appreciate all of the advice and particularly the  link which I will go to and read shortly.  I would think that an alloy such as 5160 should show a fair number of bursting carbon sparks since it is 0.6 carbon.  This material shows no bursting sparks.  I normally use 3/8 drill rod for my springs and it is very dependable for that.  In this case I was making a mainspring for the miquelet lock in the over the back fence section and the spring at its widest point was over 1" wide and in my case I made it .1" thick.  (the original was .2" thick)   I was trying to avoid spending $20 for a piece of 5/8" drill rod but in the end I bought some and made the third spring from that and so far have had no problems.
     Relative to temperature to draw to, I have gradually inched up from the high 600s to now 740 F as measured with a lead thermometer.  Much below that and the springs usually break.  I make 5 - 10 mainsprings a year out of drill rod and apart from the leaf spring steel, have not had one break in several years (touch wood)
      Some of the material in farm implements is not what you might expect.  I scavenged a couple of teeth from a tractro drawn hay rake since they would probably be some sort of spring material; no so --- these ones were mild steel.  On the other hand, I have the remains of a disc and it is a dandy high carbon steel as are garden shovel blades.

cheers Doug

[Jim Kibler]

This has been said by several times here, but I'll repeat it again.  In my opinion for the amount of work required to make a good mainspring it is false economy and foolhardy to employ re-used material unless you know exactly what the grade is.  Known material can be purchased for relatively little cost.  With known material, proper heat treatment can be determined.  The heat treatment needs to be matched to the material.  A mainspring is highly stressed and things really need to be right or the chances of it not working out are pretty high.  Other less stressed springs used in gunmaking (box springs etc.)  might be a good place for re-used material. 

[rich pierce]

There is spring steel in many period gunsmith inventories.

[Blacksmoke]

Doug:   Tim and I have both made main springs out of OLD vehicle leaf springs and they work well.  The main criteria is OLD springs.  As mentioned Model T or Model A springs.  These are just plain spring steel.  Modern leaf springs have all sorts of composite metals in them in an attempt to "improve".  It might improve the making of a spring but not necessarily the function of a spring.   Also I never use a molten lead bath to draw temper - I always use the "color" method in shaded daylight.  Then I will do it twice to make sure the spring is tempered all the way through.  If you can find Old buggy springs from the 1800's even better!           Hugh Toenjes

[JCKelly]

Jim Kibler - thanks for the reference. I think I lost the original, in one or the other Computer Death.

Yes, buy some new steel of known chemistry. It is so much easier than hoping you get the correct vintage wagon/truck/T-model spring. There is no law that says all truck springs, harrows & files must be made of the same alloy forever.

Get thee to mcmaster.com, look under Raw Materials & zig-zag your way down to steel, sheets, bars & shapes. The most forgiving steel to use for springs is listed as 1074/1075.

The finest lockmaker ever lived in this here US of A, gone now, sadly, was known to send me an occasional beautifully finished spring in two pieces. The letters were somewhat tear stained but I could figure them out. No. 1 all time reason-- tempered too hard. Like, Rockwell C50.  Last one was some scrounged steel, nice chemistry but it had a seam, would have been harmless for the intended purpose of this metal but didn't do so well as a mainspring.

mcmaster.com.  Go there. Spend some bucks upfront & discard your blood pressure medicine.

[Acer Saccharum]