Hardening a Part

[TomP]

I looked around for a replacement lifter for my Iver Johnson Supershot Sealed Eight revolver for over a year and never found one.  Finally a very nice gentleman loaned me the lifter out of his revolver for me to measure and copy.

Now the question is what material should I use.  The lifter that I copied seems to be case hardened.  It is file hard.  Will any kind of steel work so long as it can be case hardened?  Is there a way I could case harden it myself?  Would I be better off using some kind of hardenable tool steel?  

The lifter in this revolver connects the trigger to the hammer.  It pushes back the hammer when used double action and it pulls the trigger back when the hammer is cocked single action.  The top of the lifter is a transfer bar which lets the hammer reach the firing pin.  Yep, this little piece is the heart of the famous Iver Johnson "Hammer the Hammer" safety feature.

[gunnut69]

Firstly let me advise that the part you are seeking to make is a difficult one. I would advise looking for a erplacement part.. The steel used for casehardening is a mild steel. That is it has too little carbon to appreciably harden by itself. The are several methods of case hardening but for parts such as this I prefer CaseKnit(sp.). It's a powdered material available from Brownells. In use one just heats the part to a bright red and coats (just dunk the part) and heat until the powder that sticks melts. Then plunge in cold water and remove the scale. The metal should be a dull  gray. Too improve the depth of the case the sequence caan be repeated as needed. Be certain the part is properly fitted and polished before hardening. There will be no spring to the part but the core will retain it's resiliacy while the exterior will be glass hard. If this is done with carbon steel it will be brittle all the way to the core and surely will shatter in use.

[TomP]

Thanks for the advice, gunnut69.  I'll keep looking for a replacement part but I'm running out of places to look.

I finished measuring the lifter and drew it up in Solidworks (a 3D modeling program).  I have access to a programmable milling machine and a shop that does wire EDM.  So if I've done my job good enough, I should end up with a good part.

Your point about heat treatable steel makes sense.  If the entire part is hard enough to resist wear it will probably shatter when the hammer hits it.  I'll try the mild steel case hardening route.  I found something called Kasenit.  That must be the stuff you were talking about.

Wish me luck!

[michael orlen]

I wouldn't recommend case hardening for this part. Use a higher carbon steel and harden it to glass hard; then draw it, as you would a spring to toughen it throughout....

[gunnut69]

Point is well taken Michael but the case hardened part will ususally give longer life, in my experience. The transfer bars on the savage 22-410 guns last considerably longer if made of mild steel and cased. The spring steel will inevitably chrystalize before the mild steel used in the casehardened part. The one caveat is that the case must not be applied son deep as to nearly meet in the center of thin forms..

[TomP]

Speaking of the form of this part, it has sections that go from .045 to .175 inch thick with sharp corners in between.  I'm thinking that if I tried to quench a lifter made from higher carbon steel it would probably crack.

Been reading up on Kasenit.  Apparently you can increase the case thickness by re dipping whatever area of the part needs it.  That's good, then theoretically I can keep the case thin where the part is thin.

I could post a drawing of this part if anyone wants to see it.  What do I do first, put it in the GBO Photo Album?  How do I do that?

[michael orlen]

If a cracking problem is possible, using a case hardening compound with a piece that's .045" thick would have the same result...if the part is really that delicate, you will probably have to do it in an oven.

[gunnut69]

Of course we could simply NOT case the thin area. Then it should behave as would any mild steel when heated and quenced. It wouldn't cause a cracking problem then. I really don't know the penetration depth of CaseNit but doubt it's .020+..

[Plink]

Gunnut, would that work for SKS sears? I've been doing trigger jobs on them for years, but have always had worries about the quality of steel in some. Whenever I'm in doubt, or the steel doesn't feel right when I work it, I replace it with new. But I've been wondering if it wouldn't be a better idea to just adjust the sear, then case harden to as a precaution.