Assembly of Lock Castings

–Mark SIlver
(Using Parts from the Rifle Shop)

1. Determine the screw diameter for particular lock (size may range from #4
   for small British locks to #10 for musket locks). I modify Siler 6/40 or 8/32
   screws whenever possible.
2. Most reproduction lock plates have discernible tumbler and bridle screw
   locations. Check to make sure that the spacing of bridle and plate correspond.
3. I use an insta-cure glue to spot secure the bridle for drilling bridle and sear
   screw holes.
4. The tumbler pivot hole in the lock plate may be anywhere from 0.250″ to
   0.375.” Having several reamers in inventory is helpful.
5. Many tumblers do not have a fly recess cast in them. For use with set triggers you will need to drill a fly pivot hole and use gravers to chisel out a
   recess.
6. Most plates do not have a slot for the sear spring pin to fit into. I use a flat
   graver to chisel out a slot after drilling the seat spring retaining screw and
   pivoting the spring into place to mark location.
7. I’ve noticed a tendency for the mainspring retaining pin hole to be poorly
   placed. This may be due to the inconsistent shrinkage of castings. I compress the mainspring and place the toe into proper alignment of tumbler at full cock. Mark the pin location on plate and drill for proper size.
8. Some locks do not have a frizzen support bridle. You will need to make up
   your own frizzen screw on a lathe. The diameter of the screw head should just cover the pivot boss of the frizzen. I like to make the body of the screw
   reasonably large. The thread diameter should step down to create a shoulder (stop). The screw should shoulder up against the plate to hold the frizzen closely, but not tightly enough to bind.
9. The tumbler and frizzen should be water quenched from 1550 degrees F
   and annealed at approximately 500F. A kitchen oven will do the annealing
   nicely.
10. Springs should be water quenched from 1550F and annealed at 800F.
    I use a furnace for annealing. A lead pot with a thermostat also works.
11. These frizzens require carburization in an airtight box at 1550F for four
12. hours. I use a carbon pack that is 50% charred bone meal and 50% charred
13. crushed apricot pits. Water quench the frizzen (1550F). Anneal the pan cover section and pivot area at 500F to avoid breakage. I hold the parts at annealing temperature for about an hour.
14. These lock assemblies usually require a little adjusting of the spring
    tensions. I personally advocate a strong mainspring and reasonable resistance from the frizzen spring. My rudimentary physics remind me that the creation of heat requires energy. The energy is generated by the stroke of the hammer.
    Variables effecting energy generated are primarily spring tension and the
    distance traveled.
15. There are very different flint requirements for some of these locks. I
    think some people use flints that are smaller than optimum. Remember, we want to maximize sparks! I like a flint that is about as wide as the frizzen. This also evens out wear on the frizzen face.
16. I’ve found it takes most of a day’s labor to assemble one of these sets.
    However, you will have a lock that is stylistically correct for your needs and
    which will function very well.