HDTDT? Drill a case-hardened lock for side bolts?

[rich pierce]

It is my understanding that most 18th century locks used on American built guns were imported and case hardened.  Were they case hardened as imported or were the plates case hardened after the side bolts were drilled and threaded?  If they were case hardened as delivered, how did they drill the holes for the side bolts?  Did they spot anneal? What is your best guess if we don't have a definitive answer?  Or were they already drilled and threaded for side bolts? (seems the least likely answer)

[Jim Kibler]

As I understand it, they were often already drilled and tapped for the bolts and the bolts were sometimes provided as well so a thread match was insured.  I beleive I got this information from either Wallace or Gary. 

[T*O*F]

Case hardening is only a skin on the iron used for the lock.  I think one whack with a spotting punch would easily put you thru it and into the soft metal underneath.  Drilling would then be easier..

[Jim Kibler]

It's hard for me to imagine how a center puch would displace the hard case sufficiently to put a hole through big enough for a lock bolt without the bit dulling?  A case only a few thousandths thick, perhaps, but I do beleive cases on original locks were signigicantly thicker than this.  I know if I were to try to center punch a lock plate I've case hardened, I would probably end up with a dull punch and a pretty small mark.  Just my thoughts.

[flintriflesmith]

I believe that there are two answers to this depending on the quality of the lock and the period:

1. Some original locks, especially the cheaper imported so called "trade locks," had the internals cased but the plates were left soft.
2. Better locks appear to have had the plates hardened and those had the holes drilled and tapped first. One document discovered by Harold Gill when he was researching his book on colonial Virginia gunsmiths seemed to indicate that the lock bolts were included with the lock.

Gary

[James Wilson Everett]

Guys,

If the case hardening is done using only carbon, the case can be annealed or stress relieved just as in high carbon type steel.  Remember that case hardening with carbon changes the iron surface into high carbon steel for a few thousanths of an inch in depth.  When I case harden I do it in two steps.  First is to carburize the surface by heating the iron orange hot in the presence of carbon and the absence of oxygen (hot charcoal and the parts in a sealed metal container) for a couple of hours.  Next the parts are removed, reheated to orange and quenched to harden the surface.  If I need to do any work on the part it is a simple thing to heat to deep blue and allow to cool (stress relief).  Now the part can be filed or whatever.  It can be rehardened at a later time.  Warpage can be adjusted by stress relief, straightening, rehardening.     

Trying to carburize and harden in one step has resulted in some nasty steam scalds and other nasty things, so I have repented of that.  I dare say some of you guys have had the same experience.

I do not know if this will work with modern compounds like Kasenit or such stuff, I do not know what is in these, but it does work easily with charcoal case hardening.

Conclusion, a case hardened lockplate in the 18th c could be steess relieved, drilled, tapped, and then rehardened.

Jim Evertt

[Longknife]

Here is a lock from a VA rifle marked Zollman (in the library)that has a lock marked C. Bird & Co., (circa 1814) The lock was aparently made in flint, converted to perc, and badly re-converted. You can plainly see the forward lock bolt hole, which is threaded, but the rifle was made with only one lock bolt. This suggests to me that these commercial locks were drilled and tapped for the lock bolts when made, although some gunsmiths didn't use both bolts. This also questions the "one lock bolt, it was made as a percussion" theory......Ed

[rich pierce]

Good stuff.  Jim Everett's posts on the Fry gunsmith tools show a lot of long taps that could have been used to tap the lockplate while the lockplate was in the gun, so it may have been done different ways depending on how the lock was delivered new.

If I encounter this situation I will try to spot anneal particularly at the nose of the lockplate using a red hot rod pressed against the nose.  The nose of the lock, that is!