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

[Spencer Yost]

Helicoil as others suggested.   Metric bolts give you more options diameter wise, but a metric bolt on an antique canon would probably cause the universe to implode. (-;

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Spencer Yost
> On May 1, 2019, at 12:00 PM, Stephen Offiler <soffiler at gmail.com> 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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