left-handed Alex Henry/Stanton/Bob Roller lock. Part 7. Case hardening

[Rolf]

Last chapter.
All six locks are finished, and the tumblers, sears, bridles and screws caseharden and annealed in an electric heat-treating oven. The fly and tumbler link are made from 1075 steel and heat treated the same way as the springs with an oxy-acet torch. The fly was left hard. The link was annealed. The hammer and lock plate are left soft so they can be engraved.

The crucible.
I used a 5” long piece of stainless-steel pipe that was 5”in diameter. The bottom was a piece stainless – steel that was mig welded on with a wire made for stainless. I tried using mild steel pipe, that only scaled and flaked through after two test runs. There is no flame in an electric oven to use up the oxygen. Stainless steel does not scale and flake.
The lid is just a scrape of 1/8” mild steel. If you look at the lid, you can see the top flaking off. No scaling and flaking on the bottom of the lid, where it had covered the pipe.

The crucible was big enough for two sets of parts. I marked one set with soft iron binding wire to avoid mixing up the parts. I cut two strips 1/6” steel, drilled and threaded holes for the lock screws. The screws were screwed into the strips before placing in the pack. This saved a lot of frustration hunting for small screws in a bucket of charcoal and cold water.

Charcoal pack
I used 1part bone charcoal mixed with 4 parts homemade birch charcoal by volume.

I laid down a bed about 1,5” thick of this mix in the crucible, laid the parts on top. I then filled the crucible, leaving a 1” airspace on top.

Heat treating
This was done outside on the porch. It was -20 Celsius (-4 Fahrenheit) outside.

The oven was preheated to 850 Celsius (1560 Fahrenheit). It took 2,5 hours to reach that temperature. The packed crucible with the lid on was place in the oven using a pair of forging gloves.


The temperature fell immediately to 550 Celsius and took half an hour to reach 850 Celsius. I the reset the timer/thermostat for 2,5 hours at 850 Celsius.
After 2,5 hours the lid was removed with a pair of forging tongs while still in the oven. A large monkey wrench was used to grip the rim of the crucible lift it out and dump the contents in a 5-gallon bucket of cold water.


Man, I’m glad I did this outside. My wife would have murdered me if I’d done it in my cellar workshop.
 
Annealing and cleaning.
The oven was reset to 280 Celsius (536 Fahrenheit) and the parts soaked for 45 minutes, then cooled at room temperature. They were cleaned by tumbling for 6 hours with dish soap and steel shot. Please ignore the white stuff on the bridle. That’s tissue paper I dried the parts with. There was no distortion or scaling. The parts are an even grey and hard.


Depth of casing.
I did a trial run with some rejected parts and cut them up and etched with nitric acid. The depth seems to be about 1mm (0.04”) on the sear and bridle. Couldn’t get good pictures, it’s too small to show up. The screws appear to be hardened all the way through. The next picture shows two Brownells number 4 screw blanks. The one to the left is not case harden and you can just about tie it in a knot. The one on the right is case harden, but not annealed. As you can see, it broke straight off.


How much charcoal was consumed?
I strained, rinsed and dried the charcoal from the water bucket. It seems that less than 20% by volume was consumed. What left looks completely reusable. Has anyone tried this?


Finished locks.


Close up of a lock


Best regards
Rolf

Links to the other parts:
left-handed Alex Henry/Staton/Bob Roller lock. Part 1. Lock plate and Hammer
https://americanlongrifles.org/forum/index.php?topic=73225.0

left-handed Alex Henry/Staton/Bob Roller lock.Part2. Four post bridle and screws
https://americanlongrifles.org/forum/index.php?topic=73497.0

left-handed Alex Henry/Staton/Bob Roller lock. Part3 The tumbler.
https://americanlongrifles.org/forum/index.php?topic=73935.msg736278#msg736278

left-handed Alex Henry/Stanton/Bob Roller lock. Part4. The sear and searspring.
https://americanlongrifles.org/forum/index.php?topic=75495.msg750459#msg750459

left-handed Alex Henry/Stanton/Bob Roller lock. Part5. The fly.
 https://americanlongrifles.org/forum/index.php?topic=77291.msg765744#msg765744

Left-handed Alex Henry/Stanton/Bob Roller lock. Part6 Main spring & link.
https://americanlongrifles.org/forum/index.php?topic=79419.msg782932#msg782932

[Clowdis]

I see that the fly and tumbler link are 1075 steel. What grade steel were the other parts that you hardened made from?

[Rolf]

I see that the fly and tumbler link are 1075 steel. What grade steel were the other parts that you hardened made from?

Hammer, lock plate, bridle and sear are 1018 mild steel. Don't known what Brownell uses for their screw blanks.

Best regards
Rolf

[JPK]

The used charcoal can be dried and reused. I’ve done it and it will make parts hard and colorful if not polished off.
IMG_0255 by Oliver Sudden, on Flickr

[ScottH]

Rolf,
 Congratulations on completing your locks project! We have been following your progress since you started posting in September of 2022.
Amazing dedication and skill! Can't wait to see you use one or more of these locks on a rifle!
Cheers! 
Scott

[Clowdis]

Hammer, lock plate, bridle and sear are 1018 mild steel. Don't known what Brownell uses for their screw blanks.

Best regards
Rolf


Thanks Rolf! Looks like it worked out really well, nice work! Brownells screws are probably something like 12L14.

[Martin S.]

Thanks for explaining this.

Can you tell us the model and brand of the heat treating oven?

Any idea where to buy one?

I can see where one would be useful.

Thank you.

[Rolf]

Thanks for explaining this.
Can you tell us the model and brand of the heat treating oven?

Thank you.

Have a used SC3 paragon oven that's over 30 years old, and given to me by a jeweler. They are still made.
Here's a link to paragon  https://paragonweb.com/product/sc3-series/

If you google heat treating ovens for knife makers, you'll find a lot of options produced in USA.
But, they are expensive, 1500 -3000 USD.

A much cheaper solution is to make your own. There are a lot of great YouTube videos on this.

Best regards
Rolf

[Martin S.]

Thank you.