Ferguson Breach threds

[jason0012]

I got involved in a discusion with a guy who is building a Ferguson from a kit and the question came up of how the threads were cut. The kit is likely an investment casting. The threads are 11(!) start one inch pitch and tapered. How on earth would these have been cut in the 18th century? I am thinking they would be a challenge in a modern machine shop. Could they be broached or is the pitch too steep? a tap would be a dicey proposition as well. I am kind of stumped- anybody know?

 

[Larry Akers]

They would have been cut in the 18th century just as they would be cut today in a modern machine shop--on a lathe. Cutting multiple threads on a lathe is not hard if you know how to do the setup.

 

[Zonie]

They may have used a tap and die to cut the multi-start, 1" lead thread.

As LJA said, a good lathe operator can cut threads like these so the first step would be to create the taps.

Once made, the taps would be used to thread the dies which would then have the holes needed to create cutting teeth machined into them.

Once these tools are made, threading the gun parts would be fairly simple.

As for your friends parts, the external threads can be cleaned up with some careful filing.
I'm not sure how I would attack the internal threads without a special tap.

For probably a small ransom, I think I would try to get a local machine shop to make the tap, using the threads on the breech plug as a model of what is needed.

 

[Gustavo Hoefs]

Pipe thread is tapered thread 11 1/2 -1 is a standard size are we positive this breech thread is 11 - 1 ? If it is a standard NPT taps and dies are commercially available. You could use a "thread file" maybe on the plug. Or how about getting an extra breech plug make it into a tap ? dress it up cut some slots for chip relief then case harden it?

 

[Larry Akers]

Pipe thread is tapered thread 11 1/2 -1 is a standard size are we positive this breech thread is 11 - 1 ? If it is a standard NPT taps and dies are commercially available. You could use a "thread file" maybe on the plug. Or how about getting an extra breech plug make it into a tap ? dress it up cut some slots for chip relief then case harden it?

the threads are not 11-1; there 11 separate, parallel threads (leads) with each one making 1 turn in 1 inch.

 

[ddoyle]

You'd have to ask Durs to get a definitive answer but if you have access to an academic library (justor) some insight could be gained by reading Precision Screw Cutting in the 18th and 19th century (or is it 17th and 18th?) Available on sci-hub. 400 page thesis.

Once you digest the fact that scew cutting back then was as advanced as it is today it is easy to start making guesses.

Next step is to read Martin Cleeve's book on screw cutting.

Then make some more guesses.

Then read Cowan's comments in Dewitt's book on Flintlock military rifles. If nothing else take from Ernie the fact that Screw Breech Arms are not suppose to puke hot gas in your face! (lap for a seal)

All I know for sure is that 900 dollars for a barrel breeched with a ferguson action is stupidly cheap even if it takes 2 days to lap the parts into a gas seal.

Design and construction of screw breech arms is beyond fascinating and pushes everyting we know about architecture to the very limits.

The cutting of the multi lead threads is likely the most straight forward part of making a screw breech arm. getting everything to fit together as a rifle...........now that is where the magic lies.

 

[sc45-70]

Having built a Ferguson action and breech screw from scratch myself, I can tell you that with a modern screw cutting lathe it is not that big of a deal.

But depending on what source you use, the screw cutting lathe may or may not have been invented at that time. With out a screw cutting lathe, they would have to hand file out a tap. With that tap they would have to make a die. Then you could use the tap to cut the breech thread and use the die to make the breech screw.

You need to remember that these people were very talented. At this time they were hand cutting the gears and internals for clocks so I don't think making the tap and die would not have been that big of deal.

As far as the breech screw threads leaking gas, I haven't noticed any more leakage than any other flintlock.

SC45-70

 

[ddoyle]

SC45-70,

Your little 50 cal screw breech sporter is what inspired my initial interest in the "ferguson" version of breech loading multistart thread systems. Much thanks to you for having shared your work on the net. After reading your reports I found a 60 dollar cdn lathe that survived a house fire and a winter in the ditch and began trying to figure it all out. Fun stuff.

I think your perfect gas seal is the result of a couple things that are different from the cast actions and screws mentioned by the OP. You used a nice fully formed 60 degree v thread with alot of engagement on a non tapered screw and you gained at least 1 (likely more) full pitch of thread over the chamber. That is a signifigant gain in 'sealing' ability over the 2.5 or 3 pitches that fit over top of a .62 cal ferguson chamber.

Thanks again for being such an inspiration, I get alot of Joy from inching toward a command of the system that inspired Patrick.

Look forward to seeing your next project!