<div dir="ltr"><div>Cecil, I agree with the HELI-Coil as they are much stronger and tougher than the treads in the cast iron.</div><div><br></div><div>Dave<br></div></div><br><div class="gmail_quote"><div class="gmail_attr" dir="ltr">On Wed, May 1, 2019 at 12:23 PM Cecil Bearden <<a href="mailto:crbearden@copper.net">crbearden@copper.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">
<div bgcolor="#FFFFFF">
<p>What about using a Heli-Coil?? <br>
</p>
<p>Cecil<br>
</p>
<div class="gmail-m_-8828500858683130795moz-cite-prefix">On 5/1/2019 11:00 AM, Stephen Offiler
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">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.
<div><br>
</div>
<div>SO</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Wed, May 1, 2019 at 11:31
AM STEVE ALLEN <<a href="mailto:steveallen855@centurytel.net" target="_blank">steveallen855@centurytel.net</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">Gentlemen,<br>
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).<br>
<br>
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).<br>
<br>
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.<br>
<br>
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. <br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
Thanks for your attention and any input!<br>
The “original” Steve Allen<br>
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