This question is a little technical but I feel someone here may be able to help me with my understanding of trigger work.
Just how does reducing the hammer hook/sear engagement adjust trigger pull?
My physics books tell me that when dealing with friction, that if it takes X amount of force to move an object, no matter what we do to the area providing the friction, friction will remain the same. In other words, if I have a box 2' wide x 3' long x 2' high setting on the floor so that the 2'x3' area is on the floor and it takes 75# of force to move it, the same box stood on end so the area is now 2'x2', the force to move it will remain the same 75#.
This would only be true if the hammer hook/sear was mated perfectly. I doubt that any hammer/sear meets perfectly, and even if it did, the sear rotates around the sear pin and the surfaces would move out of this perfect mating and throws the whole equation out the window.
So I'm back to the original question. How does reducing the sear/hammer engagement change trigger pull?
It depends on the hammer hook and sear geometry when they're engaged.
The sear doesn't move in a straight line. It rotates. When it rotates out of the hammer hooks, the rear face of the sear crown lifts the hammer and causes it to rotate backward against the mainspring... esentially overcocking it. When the mainspring is compressed further than when it's static...i t adds resistance.
Stock hammer hooks aren't square to the hammer face. They're one degree undersquare... which adds to the amount of lift and the mainspring's resistance as the sear rotates.
Trigger jobs entail making the hooks square and mating the sear primary angle to that.
Then, the sear crown receives a breakaway angle at the rear... aka "Secondary Angle"... to reduce the amount of surface contact and shorten the distance that it has to move in order to escape the hammer hooks... and to reduce the height that it lifts the hammer when it rolls out.
It also entails equalizing the hammer hooks' contact with the sear. When only one hook is bearing on the sear... and that happens a lot with stock trigger groups... it tends to concentrate all the force of the mainspring on one small point instead of being divided evenly between two. It also places the sear and hammer in a slight bind.
The hammer hooks are also shortened from .027 inch to about .020 inch...or sometimes less... which further reduces the distance of sear travel necessary to escape the hooks and the amount of lift that the sear places on the hammer.
Just equalizing the hook to sear contact can often make a very noticeable difference in the trigger pull... even though it's not all that much lighter.
Finally, the sear primary angle and the hammer hooks are finished with a fine stone to reduce friction. All these little tweaks add up pretty dramatically if the triggersmith knows his stuff.
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My physics books tell me that when dealing with friction, that if it takes X
amount of force to move an object, no matter what we do to the area providing
the friction, friction will remain the same.
Not true. You can reduce friction by making the mating surfaces smoother. We don't have to keep using that same cardboard box.
Douglas, you are assuming that doing trigger work just involves reducing the amount of friction between the surfaces. Well, that is part of the story - simply polishing the mating surfaces will reduce friction. Reducing the amount of engagement alone will reduce the amount of trigger travel necessary to drop the hammer - also an important consideration. Changing the relative angle of the engagement alone will change the mechanical leverage required to perform that work. Trigger work involves juggling all these characteristics to achieve something that suits the owner, and the use of the firearm.
What could be simpler than that?
I have my head wrapped around squaring the hammer hooks and mating the sear to it. I have tuned my Springfield using the 'Poor Man's Trigger Job.' It make a major difference in the pistol. What I can't get my head wrapped around is sears with adjustable engagement.
This question came up on another forum dealing with rifles and sears with adjustable engagement to the hammer. A poster said that by adjusting the hammer/sear engagement in or out, he can run the trigger # up or down. The gent making the claim could not explain why they work, only that they do.
No one else could provide an answer either. As I have found some major talent on this forum I thought I would ask here. I realize this off topic on the 1911 forum.
Lazarus posted his reply as I was responding to 1911Tuner's reply.
I understand that hammer/sear angle plays a part. As does polishing the mating surfaces. I use a ultra fine hard Arkansas stone to dress everything for final polish.
Reducing the sear/hammer engagement does in fact reduce the travel of the sear before it releases the hammer. But the gent I had the discussion with said that reducing the sear engagement reduces the trigger pull #.
I know that there is a difference between static friction and dynamic friction, with dynamic being lower than static. But ounce you have the sear moving, the amount it has to travel should not effect the # of pull required. When the sear starts to move the force required to keep it moving should be lower than the amount required to get it started.
The only thing I though might play into the equation might be mechanical advantage. The fulcrum arm of the sear compared to the fulcrum arm of the hammer spring would change as you moved the sear in or out to adjust the engagement. Does that make any sense?
Douglas... while the sear engagement can reduce pull... it's only one part of the total equation... and a relatively small part at that.
A hard Arkansas stone is a bit rough for high-end trigger jobs. Most really good trigger men use ceramic stones for the final polish.
The sear spring plays a big part in reducing trigger pull weight. By bending the center and left leaves backward, you reduce the resistance to the trigger's movement, and the resistance to the sear's movement... respectively. Most trigger smiths set these at a half-pound or so per leaf. A full 2-pound reduction can often be obtained by just tweakin' the spring.
A trigger that's smooth makes it feel like it's less than it actually is. Couple that with a very short release, and it gets crisp... like the proverbial glass rod breaking. Combine the three, and a 5-pound trigger will make you swear it's 4... and a 4-pound trigger will be almost scary. Add a stop screw that reduces pre-travel... and it suddenly becomes a "Hair Trigger" that we read about in the hoorah action/adventure novels.
Further friction areas are the trigger bow and the track. A tiny reduction there adds to the whole... or subtracts from it, as the case may be.
In the final analysis... an engineer's dictum applies. To wit:
"Nothing is everything, but everything is something."
Trigger jobs are made of adjusting several little things to create a total effect.
Thanks for the tip on the ceramic stones for a final polish. Need to add that to my tool list. I thought the ultra fine hard Arkansas was good for the final.
I realized the effect the springs have on the trigger pull on the 1911. After I tuned mine I found the pull a little lighter then a wanted. It was sweet, just a little too light for comfort. Added a little more spring into the mix and now it works great.
Agree with Tuner about the Hard Arkansas stones not being the finest for the trigger sear and hammer hook polishing. The Hard Arkansas stones now sold as ultra fine aren't really. Now a 50 or a hundred year old Translucent Arkansas stone... now that one would do the trick. I had a beauty of a translucent bench stone that my apprentice drop tested. (There isn't an emoticon sad enough to illustrate my feelings here) and I would pay dearly for a true translucent stone in 6"x1/2"x1/2".
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Add a stop screw that reduces pre-travel... and it suddenly becomes a "Hair
Trigger" that we read about in the hoorah action/adventure novels.
Please define "Hair Trigger"
A stop screw does not reduce trigger pre-travel, the tabs on the front of the trigger bow do that. And the tabs that reduce pre-travel do nothing to the weight of the trigger pull... so not sure where the "Hair Trigger" is coming from.
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so not sure where the "Hair Trigger" is coming from.
From Phillip Marlowe stories of his adventures and his many deeds of derring do.
psst. Brother Wichaka. It was in parentheses. *wink wink*
As with all trigger jobs, a question has risen.
What is the difference between a crisp trigger and a roll trigger?
A "roll trigger" does not necessarily preclude a "crisp" trigger.
A roll trigger is a normal, positive trigger job, with the primary angle and the back angle of the sear meeting with a slight radius to break the corner. In other words, the primary angle "rolls" into the back angle.
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A "roll trigger" does not necessarily preclude a "crisp" trigger.
A roll trigger is a normal, positive trigger job, with the primary angle and the back angle of the sear meeting with a slight radius to break the corner. In other words, the primary angle "rolls" into the back angle.
A positive trigger meaning the hammer is cocked further will result in a rather hard trigger pull.
The term roll trigger may mean different things to different folks. But I've never heard it described as rolling into the back angle. It is simply cocked by the slide and the slide releases the hammer to the control of the sear. The roll part is when the trigger is pulled and is a long smooth pull, that doesn't break crisp, but goes off with a smooth pull of required pull weight. Normally long hammer hooks and a radius sear nose.