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

[Cecil Bearden]

I would have to disagree on the fine thread holding more in Cast iron.  
When I did a lot of Perkins engine work in the late 60's and early 70's, 
those fine threads gave us a lot of headaches and required many Heli 
Coils. Heli Coils were really expensive back then....

Cecil

On 5/1/2019 8:39 PM, Bob Brooks wrote:
> Steve
>
> A fine thread would be stronger and hold better than the coarse thread
>
> Bob
>
> Sent from my iPad
>
> On May 1, 2019, at 12:00 PM, Stephen Offiler <soffiler at gmail.com 
> <mailto: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 <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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