[AT] OT: Cast iron work on a replica cannon

[Cecil Bearden]

What about using a Heli-Coil??

Cecil

On 5/1/2019 11:00 AM, Stephen Offiler wrote:
> Probably not a show-stopper, Steve, but going up to 9/16"-12 is only 
> borderline big enough.  Tap drill calls for 31/64 (0.484").  Your 
> worn-out 1/2"-13 threaded hole had a major diameter, before wear, of 
> 1/2".  So when you drill out that hole with the 31/64" drill, the old 
> threads will not be entirely gone.  I don't know if that might mess 
> with getting your 9/16"-12 tap started, or cause any other problems.  
> I'd probably still be going for it, myself, since you have stated 5/8" 
> is too big for other reasons.
>
> SO
>
>
> On Wed, May 1, 2019 at 11:31 AM STEVE ALLEN 
> <steveallen855 at centurytel.net <mailto:steveallen855 at centurytel.net>> 
> wrote:
>
>     Gentlemen,
>     There is a wealth of brains, experience, and good horse sense on
>     this list, and I would like to pose an interesting but OT question
>     (tractor reference:  the same skills and tools and problems apply
>     to working with old iron of just about any kind).
>
>     To begin:  one of my hobbies is re-enacting the American Civil
>     War, and I am half-owner of a reproduction artillery piece. It is
>     a replica of one of 30 guns made in St. Louis during the war by
>     the Excelsior Stove Company (eventually became the Charter Oak
>     Stove Company).
>
>     While the ignition system for pieces during the period was a
>     Friction Primer (a small diameter tube with fine gun powder
>     sparked by pulling a serrated wire coated with fulminate of
>     Mercury from its top while the bottom was inserted in the vent,
>     the hole leading down to the breech), the ignition system on this
>     replica uses shotgun primers and a hammer (tripped by pulling the
>     lanyard, very similar to some modern systems).  The vent is
>     drilled through a ½” fine thread bolt which is screwed into a hole
>     in the top of the tube at the breech.  The tube is cast iron
>     around a steel liner (we do not use projectiles with this replica,
>     as the tube was not designed for those pressures).  To summarize: 
>     the hammer is held onto the top of the tube by a bolt threaded
>     into the iron; the vent is a ¼” hole drilled through the bolt, and
>     a shotgun primer is placed at the top of the vent to be struck by
>     the hammer.  The overall thickness of the tube at this location is
>     2 5/8”; the thickness of the steel liner is just under ¼” so the
>     thickness of the iron of the tube at this location is right about
>     2 3/8”.   The current vent bolt is 1 ½” long, meaning that it does
>     NOT engage the steel liner.
>
>     This tube is about 30 years old, and the threads in the tube
>     itself have become worn so that the bolt will not tighten into the
>     hole anymore.  The result is that, when a round is fired (4 – 6
>     ozs of coarse cannon grade black powder), the bolt will no longer
>     remain in the hole.
>
>     My proposed solution is to acquire a 9/16” – 12 (Coarse thread) 3”
>     long bolt (it will have to be cut down and drilled) and a matching
>     drill bit/tap set.  I intend to open up the hole in the tube to
>     the bigger diameter and thread the hole with the new, coarse
>     threads.  My hope is that I can also catch the steel liner with
>     the threads, but I don’t know whether or not the hole in the liner
>     is larger than the hole in the surrounding iron.  Drilling the ¼”
>     vent in the bolt is beyond my capabilities—I don’t even have a
>     bench drill press much less a lathe—so I will need to farm that
>     job out.
>
>     I do not want to go as big as a 5/8” bolt because the hammer
>     bracket will only accept a hole about 9/16” without jeopardizing
>     its strength.  I would like to use a coarse thread in the
>     assumption that meatier threads will wear better.
>
>     My question to anyone still awake at this point is this:  do you
>     see any fatal flaws in my plan or reasoning?  I know that most
>     here have much more experience at these kinds of jobs than I do,
>     so I hope that, if there is a flaw, someone will see it.
>
>     Thanks for your attention and any input!
>     The “original” Steve Allen
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