Four Screw British lock, by Jim Westberg

[Acer Saccharum]

 I need to make a lock for a British sporting rifle and will post pictures and notes of progress.Below you can see some parts that I had lying around that I can use.  Lock plate, bridal blank, original mainspring and a tumbler blank.  The lock plate is just a blank from mild steel, the tumbler blank is of O-1, and I dont know what the bridal blank material is but suspect it is 8620.  Bill Roberts (now Deceased) of Athens Ala used to make some best quality british locks and this piece Bill's work.  Pin locations are from an original Brazier lock.  Bill had a panograph attachment for his mill that this bridal is a product of.  It is slightly too thick and the feet were slightly too long.  I shortened the feet and will thin the body about by about .025 or so later.More on the bridal.  Below you can see the tool that cuts the feet.Here is the tool that cuts the screw counter bore.More laterThe hole size for the screw shank is .115, the diameter of a #4 screw is .112 so the bridal screws will be 4-48.  The diameter of the screw heads counter bore is .157.  Now I need to make the bridal screws.  They will be .112 body diameter and .155 head diameter.I want to attach the bridal to the lock plate at this time because all of the internal part relationships emanate from there in this case.  Once in place, I can use the outer bridal support stud hole to locate the tumbler hole in the lockplate as well as the pivot pin for the sear.Here is a simple but very effective tool that I use for making the screws.  The steel cylinder has a 1 counter bore on one end for standard dies and a 3/4 counter bore on the other end for smaller dies.  A 5/16 hole is bored thru the center. I put a piece of 5/16 rod in the tail stock of the lathe and the cylinder has free travel then horizontally....just locate the die on the screw blank and twist it on with mild pressure until the length of thread needed is cut.

***Created by
westbj (Jim Westberg) on 08/18/2007***

More pictures on Jim's Photobucket:

Here is a link to a bunch of lock pictures, I have not organized them or even labeled all of them.
You may have to copy the link address below into your browser to make it work.

http://s27.photobucket.com/user/Jwestburg/library/4%20screw%20lock%20pictures

[Acer Saccharum]

Here are all four bridal screws.  Notice that I left a big hunk on top and slotted the end.  In the second picture the screws are in their respective positions in the bridal.  Also notice the shank of the screws show at the bottom of the bridal feet and will need to be threaded slightly more.





Slighly out of focus, but with the screw drawn up tight, there is a gap between the bottom of the bridal foot and the lockplate.



Here are the bridal screws again.  Notice that I put some file slashes on the shank of the screws.  All of the antique Brazier locks that I have disassembled over the years have these slashes, they are witness marks for the respective screws once they have been fitted to the bridal/lockplate.  The goal is to have just enough thread on the shank so that the screw bottoms out at the same time the counter-bore bottoms out as the screw is seated.



#1 is fitted to the top left bridal hole, and so on clockwise down to the bottom right foot or #4

To fit the screws, I turned the threading die over to minimize the lead resulting in a more abrupt end to the threads on the screw shank.  Now I can use the slot in the top of the blank to turn the screw in the die until just the right length of thread is made.  Fitted one at a time you can tell when there is the correct bind on the bridal.



#1 is fitted, and in a few minutes all four will be.



more later

***Created by
westbj (Jim Westberg) on 08/20/2007***

[Acer Saccharum]

This work probably should have preceeded fitting the screws, out of sequence but here is how I located and drilled the holes in the lock plate.  I positioned the bridal so that any error will be forward and I will be able to compensate by taking material off the bolster shoulder for tumbler arm clearance.  Also the plate is sligthly oversize and does not yet have a bevel filed on the outer edges.  The bridal is temporarily secured with crazy glue.

As long as I had the bridal secured and no screws in place it was a good time to thin the bridal to its appropriate thickness.  Surface grinders are great!!!



With the bridal glued in place, I simply spotted the holes thru the bridal holes on to the lock plate with a .115 drill (the diameter of the bridal hole).  With the correct tap drill, the spot from the previous drill will guide and center it and those holes are drilled.  With the bridal still glued in place, the lockplate holes are tapped at the bench.  A little heat and the bridal easily comes off the plate and the glue mess can be removed.

More later

***Created by
westbj (Jim Westberg) on 08/20/2007***

[Acer Saccharum]

The bridal screws are fitted now and need finishing.  I made a fixture to finish the screws and hardened it.  I wanted just a few thousands of the shoulder showing and a dome to the screw head. not particularly concerned with the end of the screw for now.

Here I am cutting the big part off and slotting the head.





Here is the fixture





Put the fixture with the screw seated in the lathe and shape screw head and the end with a  #4 cut file.  Polish with 320.







Here is the lock with screws finished as far as need be now. A couple of the screw slots are slightly off center....not to worry.....the Brits often did this even on best quality locks.  Seems that slotting screws and checkering were not of great concern.





***Created by
westbj (Jim Westberg) on 08/20/2007***

[Acer Saccharum]

This is from Bob Roller on his four screw locks:

These "4 pin"locks are my favorites and I have just read the Jim Westberg article above.

I have made about 27 of these and the first one was in 1987. I borrowed an original  lock from Lynton McKenzie and made gauges from it. I made a prototype using my own methods and called Lynton and told him that I was finished with his lock and he was surprised that I was done with it so soon. I told him I had made up a lock and other than the screws it was interchangeable with his antique.

My approach to this job is entirely different from the one I just read. I make and finish the bridle first and use no dummy screws. I make the bridle from 3/8x1"Low Carbon flat ground steel and eliminates the need for a surface grinder. Screws are 12L14 and the diameter of the head are the same as the material,5/32. Tumblers are 1144 Stressproof,sears and flys are 0-1,springs are 1075. I use the R.E.Davis hammer and the Alex Henry type now made by Rod England from the Don Brown tooling.
The sear is relieved on the back side and it turns on a drill rod pin of .1094 going thru a .110 hole.
This,together with the rigid 4 screw bridle design makes for a very stable mechanism.
These locks are really simple and the fancy bridle is the one thing that makes it the quality lock that
I enjoy making. Also I've made 7 small versions for boys or rook rifles. These eat the time and are a $400 item if I make them.
Jud Brennan in Alaska wants one on the Rigby plate of which I have made only 3 and oddly enough.all 3 are in Indiana. I got the plate pattern from 2 old ones from South Africa that needed main and sear springs.Sight make Mike Neumann sent them to me because he had no spring material to make them from. I sent him a "care"package with different thinknesses of 1075.
Let me know if I can be of help on this assuming you are going to make such a lock

Bob Roller

[Acer Saccharum]

More pictures on Jim's Photobucket:

Here is a link to a bunch of lock pictures, I have not organized them or even labeled all of them.
You may have to copy the link address below into your browser to make it work.

http://s27.photobucket.com/user/Jwestburg/library/4%20screw%20lock%20pictures