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Tuning a Flintlock

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Tuning Your Flintlock
By Beowulf65

Got a lot of questions on how I work on my flinter, well here's hoe I "tune" my flintlock, hope this helps.
GEOMETRY
When flintlock geometry is referred to, it's usually one of two areas, cock to pan or frizzen snap over.
The Cock Area When the cock is in the down position the shoulder of the cock should rest on the lock plate and the tumbler should have slight clearance from the bridle. The bridle is the backup stop in case the cock or tumbler arbor fails. The bridle must stop the tumbler rotation before the mainspring comes off the tumbler hook. The tip of the main spring should be well supported by the tumbler hook in the down position . The cam/hook of the tumbler is designed so that it will transfer the pressure of the main spring with maximum force at the end of its travel. With the hammer down the mainspring acts near the end of the cam with greatest leverage. As the hammer is pulled back the tip of the mainspring moves along the cam toward the axis of the tumbler, decreasing the leverage. The stirrups in later locks reduced friction by changing from sliding friction to rolling friction. If the main spring is not retained on the hook it can splinter the wood in the bottom of the lock mortise area if the cock arbor fractures. Locks with stirrups also have this hook to catch the main spring if the stirrup breaks during cocking.
The flat surface of the pan and the bottom jaw of the cock are your main reference lines for lock geometry. At half cock, the jaw of the cock is parallel to the pan. In the down position a line extended from the bottom jaw points into the center of the pan, making approximately a 40-degree angle with it. The cock must fit very snugly on the tumbler arbor, with no play or free movement. The cock should not touch the lock plate any time during its movement until the shoulder contacts the plate. The jaws of the cock should be long enough to securely grip the flint. The cock screw is set well back in the cock and the screw top must not contact the frizzen during its movement.
The top jaw has the top slanted to the back and down slightly so that the jaw has a more effective grip at its outer edge. The throw of your lock (flint) is the distance from the center of the tumbler arbor, perpendicular to the bottom jaw.
Frizzen Area The frizzen must cover the pan in the closed position so that no light shows through when viewed from the touch hole side. The tail of the frizzen should only contact the frizzen spring, not the lock plate. The nose of the frizzen should hold the frizzen in contact with the flint until the flint just passes its bottom edge then it should snap the frizzen into its full open position so that it does not block the path of any spark into the pan. Frizzen spring tension is a balance of the frizzen spring and the main spring force. The main spring must be able to scrape the flint across the frizzen with small loss of speed while the frizzen spring maintains firm contact between the flint and frizzen. The flint produces sparks by scraping off white hot particles of metal from the frizzen. On a correctly hardened frizzen these will be abundant and white hot. On a soft frizzen there is not enough friction during this cutting action and particle do not become hot enough. On a frizzen that is too hard particles cannot be scraped off. A correctly hardened frizzen will usually test in the 55+ range on the Rockwell scale. This is about the same hardness as a quality knife blade.
FRICTION-POLISHING
Friction is the major enemy in every lock. Lock filers went to great lengths to reduce friction wherever possible. The stirrup main spring reduced friction by changing sliding friction to rolling friction. Roller were placed on the frizzen spring, again changing sliding friction to rolling friction, slight shoulders were added to the tumbler and other parts creating "Frictionless" locks. Any place on your lock where metal touches metal should be polished and lubricated. The lock plate itself should be perfectly flat inside. The tumbler should be held by the lock plate and bridle so that it rides on only those two points (lock plate arbor and bridle) or as close to that state as you can get it. If either the plate tumbler hole or bridle hole is oversize this may be impossible without parts modification or replacement. You can polish anything you choose for appearance. Polished surfaces are more resistant to rust. Caution: over polishing can reduce the size and strength of parts.
FLINTS
Knapped flints are preferred to cut agate. Bevel up or down doesn't seem to matter, use whichever gives the best spark in your lock. Bevel down can give a longer scraping pass on the frizzen surface of some locks. The flint's initial strike should not be at 90 degrees to the frizzen face, but at a slightly greater angle, a scraping action is desired, 90 degree angle will just shorten flint life. The flint needs to be held very firmly in the cocks jaws. Two materials are used for this, leather and lead. Leather is the most common choice. Lead was used mainly in large military locks. Leather has the advantage of holding the flint firmly yet providing a slight cushioning to the initial contact, which can extend the life of flints. It is the scraping action that causes most of the sparks. To hold the flint firmly, it needs to be placed as deeply into the cocks jaws as possible. This distance can be increased by notching the leather or lead for the jaw screw. However, flint contact with the screw can cause notching on the rear of your flint. It is not traditional but it improves the rigidity of the flint if it is glued to the leather. The glue must be water and solvent resistant. The best I've found for this use is the gel type superglue's. Cock screws that are drilled are easier to tighten without damaging the screw. The slot was probably used more frequently in early locks. The slot on cock screws is not tapered like our modern screwdrivers. Using a modern screwdriver will distort this slot. Use a flat piece of metal or file a screwdriver to fit your cock slot.
Keep the flint sharp and clean. Cleanliness is an important part of reliable ignition. Make wiping the flint and frizzen clean part of your reloading practice. Watch for "Shiners" when you wipe powder residue off. Knap any shiners as they appear! Shiner is the term for the dull area that develop on your flint from use. They usually have a shiney metalic color to them, therefore the term Shiners.
There is a real simple way to re-knap your flint faces. But it does require that you make a small tool. Take a large nail (about 3" to 3 1/2" common nail) and grind or cut the point off square. Then at the side of the now square tip take a file and cut a ledge about 1/8" back from the tip and about 1/2 way through the nail so that you create a "step" at the tip and on the side of it.
Next file on the side of the nail below the step so that the "front" of the step is flat and not the nail's rounded surface. (but don't go too far, leave at least 1/16" of step) Harden with a propane torch and quick water quench.
Take the nail to your flint while the flint is still in the jaws of your hammer. Cock the hammer. Put the step on the front edge of the flint, angle the nail forward towards the frizzen about 30 degrees off vertical (with respect to the flint) Tap the nail head with a small hammer just a light tap, not hard. A small piece of flint should flake off, and if you continue across the front of your flint it will re-sharpen the edge.

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