How to make steel springy?

[Fat ferret]

Hi all. I need to make a 2-3mm thick bit of metal springy. I want to bend it into the shape I need and then make it springy. I can do basic heat treating and have made fixed blade knives before but this is for a different project. What sort of steel would I need and where can I get it in the thickness I require?

Any help appreciated.

 

[Dave Budd]

when you say 'springy', how much so? I ask because sometimes just work hardening the steel by hammering it cold and then bending to shape will suffice. If it needs to be proper springy like a spring then a medium to high carbon steel can be heat treated appropriately (actual temps will depend on the alloy, but a rough purple to blue oxide is normally ok). If you are used to heat treating a particular steel for knives then you could use that one most likely. 2-3mm thickness will be industrial bandsaws, O1, small vehicle springs maybe (like an old pram), tyre irons maybe,

I could be of more help if you tell us what you are trying to make

 

[Fat ferret]

Not so springy it's hard to bend but not so weak it just bends back over time. I will have a play with some scrap anyway before starting the project.

 

[Dave Budd]

Stil a bit too cryptic there I'm afraid. if its not subjected to heat then work hardening mild/stainless should do. Or a spring steel in a normalised condition may be stiff enough without further treatment. Alternatively, forming creases/ridges in the material will allow a shape to be held in thinner stock without the need for hardening techniques (though this would be a fixed shape without the facility to bend back and forth in use).

 

[Fat ferret]

Sorry missed that bit. It was a spring for a folding knife I have in mind. I will try with the steel I usually use, just any scrap steel that will work for what I am making at the time. Hopefully just normalising will remove the stresses caused by bending in the first place. If not I could harden and then temper until I am where I want to be, obviously will practice on scrap first. If not I will pm for further advice. Thanks.

 

[robin wood]

springs for folders are quite complex things to get right, this resource might help http://foldingknives.blogspot.co.uk/search/label/spring
"scrap steel" may or may not work. Mild steel won't do it you need something with more carbon in it.

 

[Dave Budd]

Now why didn't you sany a folder spring in teh first place?! Yes it needs to be a heat treatable steel, most folks will use the same as the blade is made from since it is already there in the correct thickness. The hardness will need to be between the same as the blade and a blue spring temper depending on how hard the blade is and the geometry of the spring.

Like Robin says, the geometry is the tricky bit with springs. Follow the blog he points to, its very useful and the folk involved know their stuff