Harp Custom 1911 Pistols; Cutting Hammer Hooks on a Milling Machine, stoning a 1911 sear and trigger job.

Harp Custom
We are custom 1911 Pistols

I build precision custom 1911 pistols one at a time using modern machinery and tools. I specialize in custom 5"1911 Government model style pistols in .45acp and 3.5" Officer model, 4" 1911 and custom 4.25" Commander.



Information » 1911 Hammer & Sear

1911 Hammer & Sear

by Troy Harp

First I select and use only Cylinder & Slide brand fire-control components for good reason. For the Cylinder & Slide hammer I choose an EGW Titanium hammer strut for quicker hammer strike. The hammer is heat treated tool steel and the hooks are precisely re-machined on a Bridgeport milling machine. I use a special custom ground end mill for cutting very precise hammer-hooks at a height of .022" thousands and machine an angle less than 90 degrees that measures precisely 89.5°'s, essentially 1/2 degree under square. I understand that most gunsmiths will use a stone or file to achieve a 90° angle for the hammer hooks, cutting hooks that are much less than .022" thousands to work up a trigger pull. I know this is popular but despite others I choose a much more precise and labor intensive way of cutting the hooks, a milling machine. A pistol built for service or self-defense, the hooks should not ever be less than .021" thousands, period... Shortening or squaring the hooks was a practice that was originally done by match armorers for competition. John M. Browning's original hammer-hooks on the 1911 were about .030" thousands tall and slightly less than square. Although, with today's modern machinery tolerances it is unnecessary.

Machining the hammer hooks, on a mill, to a height of .022" thousands will result in a very safe and long life trigger. After machining the hammer-hooks, the sear nose is precisely stoned to an agreeing angle to the newly machined hammer-hooks using a professional jig-fixture. I then radius the edge of the sear called the "breakaway angle" to ensure a crisp let off when the trigger is pressed. My trigger pulls are never less than 4.25lbs., usually measuring at 4.5lbs; however, the trigger breaks like the proverbial "glass rod" and does not feel like measured 4.5lbs. Trigger creep will be gone and over-travel is at a minimum. You will get a very safe, highly reliable, professional trigger pull.


Contact:
Harp Custom Pistols
33301 Osawatomie Rd
Osawatomie, KS 66064
Phone 913-244-2329
Fax 913-755-3041


 

1. Setting up on the Milling Machine to cut the hooks.

After careful measuring of the frame hole where the hammer pin rest in and insuring the hammer is set up in the milling vice fixture, I begin to measure and adjust so I can use my special 5-flute carbide cutter to re-cut the hammer hooks to 89.5deg at a depth of .022. See the photos below of part of the set up.

Factory drop in 1911 hammer
This is a photo of a new big name brand "drop in" match hammer, as you can see viewed at 20x the surface is not good.
Measuring 1911 hammer hooks for cutting
Part 1 of 2 I am set up on the mill, after measuring, clearly you can see the lack of precision from so called "drop in" parts.
Measuring 1911 hammer hooks for milling
Part 2 of 2 Note the difference in the height of the face of the hammer.




End mill for cutting 1911 hammer hooks under square
A special ground end mil cutter that is ground at 89.5 degrees. Or another way to say it, it is 1/2 degree less than square.
Cutting 1911 hammer hooks
View of the hammer as I begin to start machining the hammer hooks. You can see how un-even things were to start with.

Cuttin 1911 hammer hooks

In this photo I am almost finished re-cutting the hammer hooks...

Milling 1911 hammer hooks to 89.5 degrees 1/2 degree less than square
This is a photo of a new big name brand "drop in" match hammer, as you can see viewed at 20x the surface is not good.
1911 Hammer hooks are now level after cutting
This is a photo of a new big name brand "drop in" match hammer, as you can see viewed at 20x the surface is not good.
After cutting 1911 hammer hooks
This is a photo of a new big name brand "drop in" match hammer, as you can see viewed at 20x the surface is not good.


2. Final Finishing on the newly cut hammer hooks and sear.

After machining the hammer hooks and surfacing the primary and secondary angle on the sear nose I begin to polish the newly cut hammer hooks and sear primary and secondary angle using three different lapping compounds that vary from 800 grit to 2000 grit.

Stoning the sear primary and secondary angles
Using a fixture I stone the sear primary and break-away angle
Polishing the sear nose with up to 2000 grit lapping compound
After stoning I begin to precisely polish, under magnification, using 3 different high grit lapping compounds
Fully prepped sear nose, primary and secondary angles finished
Using a fixture I stone the sear primary and break-away angle

Sear nose contact bi lateral on the hammer hooks evenly
After the trigger job has been completed, this photo illustrates the even contact across the sear on to the hammer hooks
 

 




After careful measuring of the frame hole where the hammer pin rest in and insuring the hammer is set up in the milling vice fixture and running true to the frame pin hole, I begin to measure and adjust so I can use my special 5-flute carbide cutter, spinning at 3,000 rpm, to re-cut the hammer hooks to 89.5deg at a depth of .022. A precision cut that simply can't be duplicated by an automated means and certainly not via the old fashion stoning or filing by hand.




Prepping the sear primary and secondary (break-away) angles to agree with the newly cut hammer hooks. The sears primary angle needs to be 90deg to the center of the sear pin hole.