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

[Stephen Offiler]

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>
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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