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<p>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....</p>
<p>Cecil<br>
</p>
<div class="moz-cite-prefix">On 5/1/2019 8:39 PM, Bob Brooks wrote:<br>
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cite="mid:DA3E0D6E-6A18-43A1-A4B0-7711F4DE63C2@hvc.rr.com">
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<div>Steve</div>
<div id="AppleMailSignature"><br>
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<div id="AppleMailSignature">A fine thread would be stronger and
hold better than the coarse thread</div>
<div id="AppleMailSignature"><br>
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<div id="AppleMailSignature">Bob<br>
<br>
Sent from my iPad</div>
<div><br>
On May 1, 2019, at 12:00 PM, Stephen Offiler <<a
href="mailto:soffiler@gmail.com" moz-do-not-send="true">soffiler@gmail.com</a>>
wrote:<br>
<br>
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<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.
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<div>SO</div>
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<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, May 1, 2019 at
11:31 AM STEVE ALLEN <<a
href="mailto:steveallen855@centurytel.net"
moz-do-not-send="true">steveallen855@centurytel.net</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">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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