Hardening Screws

[GregLaROCHE]

I recently made some screws for the lock of a 200+ year old flintlock. They work fine, but I was wondering if I should harden them? If so, what would be the simplest way to do so?
Thanks

[Bad Ass Wallace]

I make long trigger guard screws for the SMLE to mount range sights. The key is using 250 grade medium tensile steel, then simply heat to dull red and quench in used motor oil. The steel takes on some carbon from the oil and casically 'case hardens' them.

https://i.imgur.com/iMe64wK.jpg

[LawrenceA]

Aswallace said just get them so hot a magnet wont hold them and then quench. The critical part is to temper them so the heads won't break off.
Easy to find on youtube than try and describe what and how.
Depending on what you made them from may not even be necessary.

[uscra112]

Through-hardening screws without extremely tight process control is too risky. Like gears, they must have a tough core. Make from low carbon steel and case harden only, in our context. Good application for Kasenite, if you have any.

Or make from annealed tool steel, and don't try to heat treat them at all. This is what I do most of the time. I have on occasion made one from 4140 pre-hard, again doing no further heat treating.

Original flinter screws would never have been hardened anyway. High carbon steel in those times was too precious, and also too inconsistent.

[oldred]

Through-hardening screws without extremely tight process control is too risky. Like gears, they must have a tough core. Make from low carbon steel and case harden only, in our context. Good application for Kasenite, if you have any.

Or make from annealed tool steel, and don't try to heat treat them at all. This is what I do most of the time. I have on occasion made one from 4140 pre-hard, again doing no further heat treating.

Original flinter screws would never have been hardened anyway. High carbon steel in those times was too precious, and also too inconsistent.

+1 on the 4140 for screws! 4140 PH (pre-hardened) is perfect for this as it is easily machined, plenty hard for the purpose and just plain crazy strong.


Aswallace said just get them so hot a magnet wont hold them and then quench. The critical part is to temper them so the heads won't break off.
Easy to find on youtube than try and describe what and how.
Depending on what you made them from may not even be necessary.

The recommendation to heat until non-magnetic then quenching and tempering, is spot on BUT only with the right steels! Tool steels (O1, etc) or high carbon steels (1070, 1095, etc) will harden just fine using that process but the more common mild steel won't do much of anything and the only way to harden it is to case harden it. This can be done by carbon packing in a heat treat oven at high temperature and holding for a period of time or by using a case hardening compound. The case compound method is the quickest and easiest requiring only a torch and the compound such as "Cherry Red" which is easy to find and inexpensive or the aforementioned Kasenite IF any can be found, it has been off the market for several years now due to EPA stupidity! It contained a trace amount of Cyanide in a harmless form but some idiot at the EPA saw "Cyanide" and went berserk so a very good and highly valued product was banned from production despite years of safe use by industry and hobbyist alike.

[Bent Ramrod]

I’d wondered what happened to Kasenite. Brownell’s offers their own product, called “Hard’N’Tuff” that basically does the same thing.

Can’t imagine anything on a flintlock that would need the high tensile strength that through-hardening steels (properly hardened and tempered) would provide. Surface scratching, frictional wear and marring from accidents would be the only areas where hardening of parts would be required. Screw heads might be prone to marring by screwdrivers and bearing screws for the hammer and frizzen would be prone to surface wear. If you made the screws out of mild steel, the only concern would be such surface wear resistance, and casehardening would take care of this.

[Idz]

I think Kasenite was discontinued because it contained cyanide compounds. There are several alternatives such as Cherry-Red

[oldred]

I’d wondered what happened to Kasenite. Brownell’s offers their own product, called “Hard’N’Tuff” that basically does the same thing..

I "think" the Brownells stuff is Cherry Red relabeled, at least I have been told, but I could be wrong about that. Cherry Red is good stuff and works just fine but IMO it seemed the Kasenite would give a deeper case when working with large parts, I liked Kasenite better and I am really picky about what I use my dwindling and irreplaceable supply on. Yes 4140 PH is definitely over-kill for the mentioned purpose but it would still be a good choice, small diameter rods for screws cost little and it makes the job so much simpler. Just make the screw and use it as-is, it will be plenty hard enough and way stronger than necessary which is not a bad thing at all. However in this case as you correctly point out even the mild steels will work just fine as long as they machine well, some grades tend to be kind of "gummy" and come out rough with ragged threads but most will work ok. 4140 PH machines and threads well and saves the steps of having to harden then clean up the heat damaged surface, when hardened properly however the effort to do this is minimal but still with the 4140 you end up with a strong hard screw that still looks like it's new.

[waksupi]

I harden the lock bolt heads, as they are most often removed. No real reason to change the lockworks screw hardness in my opinion

[Der Gebirgsjager]

Just two thoughts on this: I made many successful screws from drill rod. Don't know what the alloy number was/is, but anything called "tool steel" should be good for the purpose. Also, one can buy kits of ready made screws of various sizes and lengths that aren't threaded, and thread them with a hand operated die or in a lathe.

[GregLaROCHE]

I just made a new screw yesterday, that goes into the cock to hold the flint for my flintlock. The old screw was stripped. I only have mild steel to work with, so I think I would be a good idea to harden it.
I looked for the product mentioned that is sold by Brownells, but since I am in Europe, I am automatically sent to European Brownells, that don’t sell it. Can someone tell me a place on the internet where I can buy a product to case harden mild steel?
Thanks

[uscra112]

You can case harden by packing the part in powdered charcoal, in some sort of closed iron or ceramic container, heating to about 1500 F., and holding it there for a few hours. Another way is to play a fuel-rich acetylene flame on it for a while.

[uscra112]

https://www.amazon.com/CHERRY-RED-TR-CHER-1-HARDENING-COMPOUND/dp/B00DHMIY1K/ref=sr_1_1?keywords=case+hardening&qid=1568351548&s=gateway&sr=8-1

I know McMaster will ship to Canada; don't know if they will ship to Europe.

https://www.mcmaster.com/case-hardening-compounds

[uscra112]

A better approach might be to find a high-strength metric bolt to make your screw from. In the States that would be Grade 8; in Europe it will be different.

Downside is that the steel used for Grade 8 bolts doesn't machine very well.

[LAGS]

grade 8 bolts can be annealed for machining, then rehardened.
They wont come back up to Grade 8, but they will be harder than Mild steel by far.
They will reharden with Flame heating, and Quenching in Oil.
A simple At Home Fix.
I have used that method from back in my mechanic days, and it works.

[country gent]

Some thing to consider here is hardening screws put more wear in the female portion of the threaded joint, this part is much harder to repair replace the threads in. I would rather have the bolt / screw go bad and have to make the new screw than have to bore and sleeve the hole for new threads. Its the simpler easier option.

Industrial case hardening ( not the case hardening done for a finish also) was done in big pots of cyanide heated to a high temp and soak time determined depth of case. This produced a very hard surface and up to .070 deep. It wasn't as prone to warping and or cracking as the quench methods used. The bone, leather, and charcoal method produced a case a little softer and around .040-.050 deep, with a [;easing display of colors in the part.

[GregLaROCHE]

A better approach might be to find a high-strength metric bolt to make your screw from. In the States that would be Grade 8; in Europe it will be different.

Downside is that the steel used for Grade 8 bolts doesn't machine very well.

It’s a 200+ year old gun and the threads don’t correspond to anything current today. That’s why I had to make one.

[GregLaROCHE]

Annealing a bolt might be a good idea. I didn’t think about that. I plan to make another one and if that method works, that could be the way to go.

The part threads into cast iron and has to take a lot of torque to hold the flint in place. That’s why I want to harden it if I can.

[uscra112]

The c.o.c.k of a flinter would never be made of cast iron. Much too brittle. It would be of wrought iron, which is quite soft, unless case hardened. I can't recall ever finding a flintlock part that was case hardened. The only hard parts of a flintlock are the frizzen and the springs. In colonial America the only source for hardenable steel was old files, and being imported they were very precious. Europe might have been different, but I'd bet not by much.