18th C Breech Threads - HDTDT

[James Wilson Everett]

Guys,

Here is another How Did They Do That?  This will show the tools and technique for threading the breech of a gun barrel using 18th C style tooling.  This is a two step process, similar to what modern M/L gunsmiths use.  The barrel is a forged wrought iron rifled barrel, 0.515 caliber.

First the breech end of the barrel is opened to the proper hole diameter and depth using a tool called a grinder.  It only opens the existing breech bore hole a bit to the proper diameter for the threading.  The grinder is used as it is one of the rare 18th C tools that would actually cut a controlled diameter hole.  The "fish tail" drill bits and tapered reamers could not accomplish this task.  Here is a photo of the grinder and tap set used.



The grinder is used with a hand brace to cut the hole as shown.  The breech end of the barrel has a significant lead-in or funnel shape to help start the rifling cutter, it would be difficult to start the rifling cutter on a square edge hole.  So as the grinder cuts deeper into the bore, it also begins to take a bigger cut as the grinder works its way through the funnel section.



The breech is cut to a depth of 0.53 inches.



Here is what the resulting finished hole looks like, 0.53 depth and 0.58 diameter.



Now to form the threads.  Here is a photo of an original 18th C set of breech plug taps alongside of the set I use.



The first tap has a long lead-in guide to keep it on center, it only forms about the first 4 or 5 threads.  This is a very easy tool to use, the tool stays properly centered and it forms or swages the threads, it does not cut.



The tools are turned using an original tap wrench.  The rectangular drive sections of the new set of taps were made to fit the old wrench.



Next the tapered tap and the bottom tap are used to finish the thread.  Again, the threads are not cut, they are formed or swaged.  The hole starts at 0.58 diameter and ends at 0.55 diameter as the threads are formed.  The finished thread size is 0.614 diameter, 20 threads per inch.



This tooling may not work well on modern steel barrels as the steel we use today is significantly less ductile than wrought iron.

Jim

[Acer Saccharum]

That is awesome, James, thank you.

[Curt Larsen]

This is great.  Thanks for posting it.

[jerrywh]

 Very good info and probably very true. The one thing that bothers me is,  the grinder doesn't have a pilot on the end.
 for the most part I think this was the process used but t here were probably some small variations. I have some original barrels that look like this was the procedure used to do the breech plug. Some of mine look like there is a slight taper to the plug about 1/2 the taper of a modern pipe thread.
  This is the most informative type of post. We don't get enough of this type. 

[Acer Saccharum]

to echo Jerry: Piloted tools are the 'cat's meow' when you are doing this kind of work without a lathe.

I add that a slight tapering of the threads is very practical from a tap's perspective. The thread forming tool will stay aligned better with a little taper. If it were a straight forming tool, you'd have a very difficult time getting it started, and the first thread of the tool would take all the punishment of forming the thread.

[James Wilson Everett]

Guys,

Right! I guess I should show some more detail of how the tools work.  The breech grinder certainly does have a pilot, in fact it is a removable pilot, although most probably this is a more modern adaptation of an 18th c grinder.

Here is a photo of a breech grinder with a replaceable pilot, just a tad smaller than the barrel bore.



The grinder teeth look like this on the working end.  Since all of the chips are captured when opening the bore diameter, the grinder must be removed frequently to clear the chips away from the teeth.



Here is a photo of the two sizes of breech grinders that I use along with some brass pilots.

[UR

As far as using a tapered thread tap.  Yes, this makes keeping the thread aligned and on center a very easy job.  But note, this is an actual tapered thread, not a tapered lead in of a straight thread like a modern plug tap- quite different.  I seem to find it rather difficult to keep modern taps aligned and on center while cutting breech threads with just a tap wrench.  Thanks for the comments.

Jim

[Acer Saccharum]

I find cutting breech threads straight with a modern tap impossible. A drill press fixture or, better yet, a lathe is a big help.

[James Wilson Everett]

Guys,

Just a bit more research on this topic.  Here is a photo of three original breech grinders.  These were used with the tap wrench type of tool and not with the drill brace as I use mine.  I cannot see if there is any indication of a pilot, but I suspect that these do use a pilot.  But, you can see that this type of tool was used to open up the larger diameter hole for the breech plug threads instead of any kind of drill bit or reamer tool.

Jim

[Sawatis]

Really cool tutorial James....thanks so much for the enlightenment!  When I made some pistol barrels up a few years ago, I cut the breech pin recess with a modern piloted counterbore...same concept I see...the taps are the most revealing to me of the process
John

[James Wilson Everett]

Guys,

Now to make the breech plug!  I start with some wrought iron bar, 1.1 inches diameter.  The thread is 0.614 inch dia, 20 T.P.I.  First I scribe a line around the bar, next cut & file the iron down to an octagon of about 0.610 inches.





Next I file the octagon to a 16 a-gon?  And to a somewhat tapered round.  Notice that this round is a good bit longer that the final threaded section.





Making the threads is a whole lot easier if you use an old style tool (modern dies are so frustrating).  Here is the tool I use, late 19th or early 20th c, but it operates in the same way as an 18th c tool.  You close the jaws on the base of the round section (Yes - the base).  Tighten the tool and rotate the tool towards the free end.  This is completely backwards from a modern die.  However, the old tool is very easy to keep the thread centered, square and aligned. It takes several passes with this tool to form the threads for a good fit.





Using the old style tool the thread can be formed to give a really tight fit into the barrel breech threads.  In this case I like to make a slightly tapered thread to help in the final thread fit-up.  Try that one with a modern die!

Measure the depth of the barrel breech threads to the shoulder, then cut the breech plug threads a little longer.



Now install the thread and begin that careful file & fit process to bring the simultaneous firm contact at both the internal barrel shoulder and the barrel breech end.  Notice with this method you do not worry at all about aligning the breech plug with a barrel flat.





Now shape the breech plug & tang correctly.  Next posting as this one is so picture heavy.

Jim

[Keithbatt]

This is just great!  Thank you for sharing.

Keith

[PPatch]

Interesting post James. I will be following it as you progress.

dave

[Curtis]

Very interesting James!  Keep it coming.

Curtis

[James Wilson Everett]

Guys,

Here is a picture of an adjustable screw stock with the split die for making a large screw thread.  It is taken from the mid-18th c Wyke tool catalog.  As with the one that I used in this topic, the smith can make threads with a variety of diameters all having the same pitch.  Or, he can make a tapered thread.  In this case the thread is 0.614 - 20.  It could just as easily be a 0.585 - 20.

If any of you guys ever see a tool like this large screw stock, grab it up and let me know!  Donations are accepted!

Jim

[Old Ford2]

Hi James,
Thank you very much for a most interesting post.
I have been in machining all my life and never gave threading much thought.
Just used the old taps & dies and went about my job.
The next time, I will give the masters of old much credit and thought.
And I will keep my eyes peeled for some old tools to add to your collection.
Best regards!
Fred

[Mark Elliott]

You can still buy split dies like shown in the catalog cut above, and I have some really old ones with a Little Giant die stock and dies that looks a lot like item #349.    MSC still has them in its catalog the last time I looked.  Is this the same thing or not?

[James Wilson Everett]

Guys,

Now to finish the breech plug.  I pick what will be the top flat of the barrel, the flat with the least amount of mistakes.  I then file the breech plug metal block down to match the selected top flat.  This way it is easier to get a nice alignment. 



The rest is just cutting away all the remaining metal to leave the breech plug shape the way I like it.  A lot of hacksaw work here.



The tang I want is the slightly flared shape (flare with a flair).  The punch mark shows the centerline location.  The tang is a bit longer than I will use, but it will be cut shorter later.  So, now it is finished and ready for a proof test.





Jim

[ShutEyeHunter]

Remarkable post!

I have limited understanding of metal/machine work so pardon the stupid question...

You mention that this was a tapered thread (not like you'd get from a taper or plug tap). Should have quoted it

Is it tapered like an NPT tap would give you?

[James Wilson Everett]

Guys,

Not a stupid question at all.  Often, the 18th c methods of metal working are so very much different from our modern methods, that our machinists of today are quite surprised.  For instance, how to make a cylindrical metal part without a metal lathe?

For the large breech plug threads, it is certain that an 18th c tool using a split die was used.  With this tool the smith can make quite a range of thread diameters with the same thread form and pitch.  The question is - How to make the proper diameter male thread for the existing female threaded hole?   The method I use is to start with a slightly tapered round pin that is significantly too long for the finished piece.  The threads are formed on the tapered pin (not cut - they are swaged) until the tip or thinnest section will engage well with the breech threads.  From then on the remaining threads are progressive worked or swaged to a proper diameter until the breech plug can be threaded to the barrel interior shoulder.  Now the threads are the proper diameter.  Next the over long male thread is cut back, I cut it back until it is only about 1 thread too long.  

The thread is not tapered full length like a NPT pipe thread.  Also, the threads are not just partially formed as with a modern taper or plug tap.  On the example above, probably only the last 1/4 inch or so is tapered.

Now begins that tedious file n fit, file n fit, file n fit until the male thread bottoms on both the interior shoulder and the exterior barrel end simultaneously.  This method of making the breech plug does eliminate the third requirement of also having the breech plug match up with the barrel top flat.

Jim

[ShutEyeHunter]

Thanks for the clear explanation.

I really like the idea of the full round breechplug.  Easy to hog off the non-tang part with a hacksaw.

The other advantage I can see (caution, long and perhaps convoluted)....

Parts like breech plugs and drums are what I'd call "safety critical fasteners"

On my motorcycles, everything but the license plate bolts are safety critical.  I would never install a fastener without a torque wrench.

But the gunsmith art is to "tighten it pretty good".  Breech plugs are probably robust enough to withstand a bit of over tightening to make it to the next flat.  Drums not so much.  In either case, I think you can way over stress (preload) the threaded bits by over tightening.

On my next build, I'm going to try the round stock breechplug method and grind some wrench flats on it so I can use my torque wrench on it.  Figure the torque specs are for a Grade 1-2 bolt with lubed threads.

I've put wrench flats on my drum for the current project & I'll post what I find out.

If this post suggests I suffer from over-analysis and OCD----guilty as charged

Thanks, again

[flatsguide]

Interesting how it was done years ago. Nice file work. I don't think 'Swiss Mills' will ever become obsolete.

[Ben Quearry]

James
Once again you have given us priceless information. Your work is amazing. I just wish someone would start making reproductions of the tools like you are using. I would certainly buy them.
Thanks again
Ben

[T*O*F]

If any of you guys ever see a tool like this large screw stock, grab it up and let me know!

I have a set of those manufactured early in the last century, called the Greenfield Little Giant.  They were my stepdad's.  I think they go from 7/16ths" to 1".

They might be for sale (after I return from Friendship).

[Pennsylvania Dutchman]

Very interesting post, Thank you. I always wondered how the early split dies worked. The Little Giant split dies are only adjustable in a small range and they must cut from the nose of the screw to the shoulder as opposed to starting at the shoulder and backing it off the nose of the thread as James explained for the early split die. Little Giant dies also cut threads instead of swaging them.
Mark

[ddoyle]

James, Thank you very much.  This thread should serve to make us all very dissatisfied with modern 'close enough' thread forms!

Seeing your pictures of screw stocks has made me painfully aware that I have left a few in junk store buckets of rust not knowing exactly what they were