sugestions on slipjoint spring

[Don Robinson]

Originally Posted by 22H2

ok re heat treated the spring 1925 for two hours, flash tempered for 1 hour at 350 and tempered at 1150 for two hour I got 42-43 on hardness. I would like to have at least 45-48 any sugestion. the spring seems to work well. just would feel better if it was harder.
thanks

I believe your spring will be OK at that hardness. The ideal hardness for a carbon steel spring is around 45Rc. How are you measuring hardness?

For everyone's sake, each batch of steel that comes from the steel mill is slightly different in chemistry. The mills must have some tolerance, so they publish a range. That means that a blade made from one batch may vary a little in hardness than a blade from a different batch of steel.

That's why I creep up a little on the final tempering temperature as someone mentioned above. Once I know the exact results of the first blade, then I use the same formula for the next blade made from the same bar.

CPM steels are much more closely controlled in chemistry than open hearth steels.

Multiple tempering cycles at increasing temperatures won't do any damage.

[22H2]

thanks Don, I have a hardness tester that I use, what is the idea spring hardness for ATS 34 I would like to be in the 45-48 range?

[Don Robinson]

I'd say anywhere between 40-50Rc. A lot depends on the size, thickness, length and width of the spring. The thinner it is the easier it flexes, so a thinner spring may operate correctly even though it's 50Rc. A really wide spring needs to be a little softer in order to operate without too much pressure.

Of course the distance from the operating end to the fulcrum, the middle pin, has a lot to do with operating pressure too.

There are too many variables to have one rule of thumb. It all depends on the geometry and steel used for each knife. If a spring is too hard to operate but heat treated correctly, the operating pressure can be adjusted by thinning the spring in the area where it flexes.

[Kirby Bletcher]

Originally Posted by 22H2

thanks Kirby, If I understand correctly you think my temper may be to high? Would it hurt anything to temper the same part multiple times until I get the hardness correct moving up in temp with each temper? Once I find the right temp can I just start there the next time or will the multiple tempers change the formula some? sorry for all the questions just trying to get the best spring that I can.

Ted

Yes Ted you understand correctly. You can draw temper the same part multiple times but do it within reason. I would suggest using a scrap peace of steel and practice with it before using the actual knife part. Yes, once you find that temp rang you can nearly start there the next time. May be to be on the safe side start at 25 degrees less for the first hour then check hardness, if it needs to be softer pop it inn for another hour at your spec temp.

No need for apology's, I had a little trouble the first time I started heat treating my own springs so I know what you going threw. Just take you time and follow the good advice you got from Don and others hear and you'll be fine.

Kirby

[22H2]

thanks Kirby and Don, I will start a test part this weekend and try to establish the correct formula for my equipment.