Hardening hacksaw blades?

[Fred_Dwyer]

OK, not exactly a building question; but a lot of folks seem to know metals a bit more than me.

I'd like to get hacksaw blades a bit more "springy." I'd like to be able to bolt 2 together at the mount holes and be able to pull them apart at the middle to about 6 inches, yet have them snap back together, repeatedly. I picked hacksaw blades only because they are already the configuration I need, and they are plentiful. I would grind the teeth off before hardening. Also any other suggestions of a long "snappy" spring like described what be good.

I have a way to heat them evenly to red, just need some temperature ideas for tempering.

[Habu]

It would seem that general scrap-metal rules would apply.  Heat it red-hot (to a non-magnetic state) then quench in oil; if that doesn't harden it, try again quenching in water.  If that doesn't work, try a different steel . . .   if it does work, anneal by flashing off in oil, or to about 650-700 degrees or so.  You might have to play with the anneal temps to avoid cracks.

I've made flat springs in the past from band mill blades (like a large bandsaw).  If you can find one that isn't all cracked from use, they work OK.  I think the steel is L6, but am not sure on that.  Blades from a panel saw (crosscut, rip, etc) might be another source. 

[rich pierce]

bandsaw blades would work tempered to spring hardness in a trough of molten lead.

[Fred_Dwyer]

bandsaw blades would work

Thanks, there used to be a saw blade shop on the other side of town. Hope they're still in business. I could get plenty of pieces there.

[JCKelly]

It does not matter how you heat treat them.

The stiffness of a piece of steel, a spring in your case, has nothing to do with how hard it is.
To make a spring stiffer, make it thicker.
Or in your case, as I think I understand it, use one more layer of hacksaw blades.

The reason one heat treats a spring is so that it will not take a permanent set, or bend, when the gun is cocked.
A spring temper just means it is strong enough that it can take the necessary bend to work in a lock, yet spring back to its original shape when the gun is fired.

Anyway, unless your spring is taking a permanent bend, heat treat won't help. Metallurgy 101.

[rich pierce]

Most of us never took Metallurgy 101.  But we did sleep at a Holiday Inn Express, so feel qualified to comment.

[camerl2009]

well you dont want them too hard about 30hrc or so too hard and thay will snap too soft and thay will bend and not go back

what you want to do is anneal them by heating to critical temp (non magnetic should work for this) and stick it in a bucket of sand or ash and let it cool down slowly then grind off the teeth make it into the shape needed then normalize it to relieve any stress in the steel so you dont (get stress fractures in the steel) then harden it and temper it to the hardness needed

for most of that your going to need to know what alloy of steel you have most high carbon steel will work but 5160 is easiest you can get this from car leaf and coil springs

most band saw blades should be 1075

[LRB]

  Mr. Kelly is dead on with his info. That is why it is really a waste of time to use spring steel and heat treat for the spring for a sliding wood PB cover. With the short distance of spring travel considered, you would never tell the difference.

[Belleville]

I recall from years ago our metallurgist at work saying that it would be difficult to make a spring out of a hacksaw blade due to not knowing the composition of the material. One of the Engineers was however successful in making such a spring.

Doc S.

[KNeilson]

I also agree with JCKelly. In my own experience, dealing with thin materials such as hacksaw blades, heat treating is difficult because of the rapidity of heat transfer in and out of the material. If you can put 4 or 6 in. out off vise jaws and put a 90 bend in it and have it return straight its heat treated. If it breaks increase tempering temps. If it bends you didnt get it hard in the first place...  fwiw...   Kerry

[Rasch Chronicles]

Fred,

You're not making an triggering device now are you???

Albert “El Matamoro” Rasch
The Rasch Outdoor Chronicles
Cold Weather Camping Tips!
ΜOΛΩΝ ΛΑΒΕ!

[Eric Laird]

Doesn't sound like it - then he'd only need it to snap back once!

Eric

[Fred_Dwyer]

No, not a triggering device. For that I could pick up any number of coil springs from Ace Hardware.

I've bent a number of hacksaw blades sawing pipe or other squirrelly materials. They are hardened, they do manage to cut other steels with ease. I just need a bit more springiness than they come with. I'll try the molten lead temper. Then work up or down from there.

[bgf]

Make sure you read Ken Guy's tutorial (I think it says banana patchbox springs, but it is generally applicable to using hacksaw blades as springs).  Hacksaw blades (I think mine are mostly Nicholson HSS?) work well for me following his procedures, including tempering in burning oil (I even tried soybean oil for a "natural" solution and it worked well)j; I think patchbox springs, for example, are so non-critical that your material doesn't have to be perfect to work as needed. 

[Fred_Dwyer]

Thanks all. This gives me a few alternatives to try.

I do have a question about the burning oil tempering. If you ignite the oil then let it burn away, I would think that the flame would over heat the piece as the oil got down low. I had figured that you slowly bring the oil to flash-point and temper in that oil, the flash-point always remaining a pretty consistent temperaure. But I suppose Ken G has excellent results with his method.

It won't hurt to experiment a bit; the worst case is I may end up with some noodly blades.

[Ken G]

The method was taught to me by master blacksmith and gunsmith, Steve Bookout.  I can say without a doubt when doing small springs for triggers and patchboxes it improved my success rate to around 95%. It works.
I have found some hacksaw blades that just didn't work.  You will know them by their cheap purchase price.  
Good luck.  Post back with results.
Ken

[Acer Saccharum]

High carbon blades are one thing, you can heat treat them like regular spring steel.

But some blades are HSS, or Bi-metal, which is HSS cutting edge welded to a high Carb body. These might give you trouble in heat treating and drilling, etc.