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

Dave Maynard dave at themaplehillfarm.com
Wed May 1 12:23:32 PDT 2019


Cecil, I agree with the HELI-Coil as they are much stronger and tougher
than the treads in the cast iron.

Dave

On Wed, May 1, 2019 at 12:23 PM Cecil Bearden <crbearden at copper.net> wrote:

> 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>
> 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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