Hi,
The tumbler finally came and I was able to get the rest of the work done. The new casting is good quality, far better than the one that came with the lock. Nonetheless, the tumbler post and bridle spindle fit the lock plate and bridle without any polishing, so truing and polishing will create sloppy fits. Fortunately, no truing of the post, spindle or tumbler faces is needed but they can benefit from polishing off the bead blasted "as cast" finish. What worked best was to just install the tumbler, bridle, bridle screw, flint cock, and sear screw, sprinkle aluminum oxide powder on the bearing surfaces and some paraffin oil. Then I just worked the flint cock back and forth to polish the working surfaces. I also lightly stoned the sides of the tumbler avoiding the spindles. You have to be very careful truing or polishing the side of the tumbler with the fly because you may take off too much metal exposing the fly above the surface of the tumbler.
I polished the sear and bridle with stones and oil and polished the curved face of the sear and the part where the sear spring touches to a mirror finish. I also mirror polished the foot of the tumbler where the main spring rides. I cleaned up and polished the flint cock.
The flat where the tumbler screw is located is larger than the screw head. I hate that so I filed the surround down until just a tiny bit smaller than the screw head. Then, I turn the screw to file and polish the head, which reduces its size just right to fill the flat on the cock. The base of the flint cock is bulgy and amorphous shaped, which I dislike. Consequently, I filed it into a more even cone that has the tumbler screw as its top.
Next I filed the flint jaws flat and then cut teeth in them with a round-bottomed die sinker's chisel. The teeth are historically correct and really work holding the leather wrapped flint. I cleaned up and polished the top jaw using a wooden jig to hold it. I stoned and polished the lock plate and the frizzen.
I installed the frizzen and frizzen spring to test the action and fit and discovered 2 problems. The fit of the frizzen to the pan was OK before but the extra pressure from the strengthened spring pushed it up and off the pan. The hole in the frizzen for the screw is bigger than the screw creating a sloppy fit plus it was drilled when the lug on the bottom of the frizzen was in place preventing a good fit. The only way to really solve the problem completely is to fit a new frizzen with the lug gone, however, I did not want to go that route. Instead, I made a 6-40 screw that fits the lock plate but was a hair too large for the hole in the frizzen. Then, using a round file, I removed metal from just the top of the hole until the screw just fit, which brought the front of the frizzen down a tiny bit. That solved most of the problem, although a sliver of light can still be seen between the pan and frizzen. The second problem was when I snapped the frizzen open and closed, I heard a clicking noise. It took me a few minutes to figure it out but it was caused by the pin on the frizzen spring moving in the much too large hole in the lock plate. When the frizzen was closed it pushed the pin down making the noise. I welded steel into the hole and drilled a new one that fit the frizzen spring. Problem solved.
The mainspring is adequate but really did not work well with a stronger frizzen spring. There is not much you can do to it because the thickness of the spring is pretty thin. I decided to forge a new and much better spring. It also looks much more like the springs used on the original looks. The length is just right such that the hook just rests on the end of the foot of the tumbler when at rest. Then it slides back at half cock and finally at full cock, it ends right at the bend in the tumbler. Notice how little lifting movement there is going from half to full cock. The hook is very close to the tumbler spindle such that the force diminishes a little as you pull the flint cock back to full.
I case hardened the frizzen, lock plate, cock, bridle, tumbler, sear, and top jaw. I harden and temper the sear, bridle, and tumbler together so they have exactly the same treatment. That means they should be of the same hardness. If you harden and temper lock internals, my recommendation is always heat treat them as a group. The plate is pretty thick so I opted not to block it with a heavier plate of steel. I oriented it in the crucible box so it was on edge as it entered the quench. The other parts were packed around the plate in a mix of bone and wood charcoal. The box heated in my oven for 2 hours at 1575 degrees and contents quenched in room temperature water. I am not interested in colors, just a hard surface. After quenching, I polished the surfaces and tempered the parts. The frizzen was tempered for 1 hour at 375-390 degrees. After cooling, I heated the toe of the frizzen to blue color with a butane mini-torch. The tumbler, bridle, and sear were tempered to 600 degrees for 1 hour. I also tempered the flint cock and top jaw to that temperature. However, the owner of the lock liked a temper bronze color for the outside of the lock so I polished off the blue on the flint cock and top jaw and then tempered it again with the lock plate to 470 degrees. I always temper the cock to 600 degrees initially because I am paranoid about it being too brittle. However, to match the color of the rest of the lock, I polished off the blue and tempered accordingly.
My last job is to make sure the mainspring and frizzen spring are balanced. First, I made sure the top of the frizzen spring, and toes of the frizzen, mainspring and tumbler were highly polished. When assembling the lock, make sure the fly is positioned correctly.
After assembling the lock, I measured the force needed to open the frizzen with a trigger pull scale. It was 3 lbs. Then I checked the force needed to pull the mainspring back from rest to full cock using a hand held luggage scale. I usually want that force to be 3 times stronger than the force to open the frizzen. I ground more bevel into the mainspring until the force was 9-10 lbs. Here is how well it sparks with a well used, dull flint.
The job is done and I don't dare count the hours. I've gone the extra mile in most everything and do not suggest anyone has to do all of that to make the lock work pretty well. Nonetheless, all I did was bring it up to a standard close to the originals and half of what I did was required just to bring it up close to par with a Chambers round-face English lock right out of the box. The end result is a good lock and it should serve its owner well but it is a shame lefties don't have better choices.
dave
