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Brownells/Marvel 1911 Sear/Hammer Jig

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Brownells/Marvel 1911 Sear/Hammer Jig Empty Brownells/Marvel 1911 Sear/Hammer Jig

Post by tovaert 11/5/2023, 12:35 pm

Despite the numerous negative reviews on the Brownells website, I put myself on the waiting list and bought one to play around with using some old parts. I was looking for something that would cut primary and secondary sear angles, and enable me to square and polish hammer hooks. With a few simple changes, the design could easily be improved. 

My delivered jig had the fundamental complaint, which is the inability to clamp a sear in place without pulling out the threaded sear post. It is likely intended to be a heavy press fit; mine was certainly not. This is a catastrophic error, IMHO. But it was tight enough to serve as a centering pin when I mounted the pin/sear jig insert on a milling machine. I opened up the the sear pin hole using new starter drills (it's made from moderately hard steel), out to 5/32". Then a #10-32 tap, and red Loctite a #4-40 internal/#10-32 external threaded insert in place. My sear jig insert was protruding about 0.004" above the surface where the hammer rides, so I polished the insert down to ~0.001" protrusion, using a lapping/polishing plate. A copper washer under the head of a #4-40 SHCS; the #4 thread fits snug inside the sear's hole, and with light torque holds the sear against the lapped face of the sear jig insert so that it won't rotate when stoning. Once the sear is clamped in place (mated with a squared hammer as a reference), you move the jig insert to "Slot B". The stoning guide serves as a reference surface and a height-adjusting 1/4"-20 SHCS adjusts the amount of sear nose that protrudes above the stoning surface. The instructions recommend ~0.006" of material removal as a start, which corresponds to roughly 45 degrees of rotation of a 1/4"-20 thread. I used a fine Norton stone followed by an extra-fine stone. The third photo shows a typical primary angle cut. Then you move on to Slot C, which allows you to stone the secondary angle. One of the weaknesses of the design (and easily fixed): there is no adjustment screw on Slot C. You have to manually raise/lower the sear jig insert in the slot and clamp it in place. If you are trying to control the sear nose "protrusion" for the secondary angle...not so easy. Also, my jig has a misalignment error likely caused during machining. It stones the secondary (surface) as an imperfect rectangle that "tapers" somewhat towards the left side of the sear. I thought that might be caused by the fact that with this jig's design, the sear is cantilevered, rather than being supported on both sides, and any flexing of the #4-40 SHCS could result in that offset under the force applied to the stone. However, it does not happen when cutting the primary angle so I figured it must be due to some misalignment/machining error. Not easily fixed either, but the error is fairly small. Another weakness, the main body of the jig is aluminum, so stoning is done sliding against aluminum, which is not good from a wear standpoint, even lubricated. There are two slots in the jig's body for the stoning guide (one shown to the upper left of my thumb), each about 1/4" wide and 0.3" deep, spaced a few inches apart. The depth could be reduced to 0.230", say, then two 1/4" dowel pin placed in the slots would make a nice rolling system with no contact between the stone and jig. That would be easy to fix. 

The hammer vise (used for squaring hammer hooks) is pretty straightforward and height adjustable, but I have not tried it yet. It appears that you have to somehow (visually?) align the hammer's flat surface ahead of the hooks, with the jig's stoning surface. I guess you then check for parallel alignment by polishing away some Sharpie ink.
 
I went back and forth a few times checking the work in my pistol until I obtained a pretty nice (and crisp) 3.5# trigger, no hammer follow-through. Will be range testing soon.

In all, I'd give it about 7/10. Sorry for the length of this post but I thought some might be curious about it.
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tovaert

Posts : 427
Join date : 2018-11-28

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Post by Wes Lorenz 11/5/2023, 3:09 pm

My .02.
Just inquiring, why would you want to square the hammer hooks when they are EDM'd to square +/-.0001?
I just polish them with a ruby stone which just burnishes the hooks.
I agree that the hooks needed to be squared on old school hammers. If you are using an old hammer, please ignore my comments.
Wes

Wes Lorenz

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Join date : 2011-06-27
Location : Washington

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Post by tovaert 11/6/2023, 8:23 am

Wes Lorenz wrote:My .02.
Just inquiring, why would you want to square the hammer hooks when they are EDM'd to square +/-.0001?
I just polish them with a ruby stone which just burnishes the hooks.
I agree that the hooks needed to be squared on old school hammers. If you are using an old hammer, please ignore my comments.
Wes
Yes...it was an older hammer.

tovaert

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Post by Shootist007 11/19/2023, 7:15 am

I have had one of the original marvel jigs, no Brownells in the name, and have used it for many 1911 trigger jobs. The stud has never pulled out on the sear piece.
But I like you idea.
I also recently bought the True Radius jig from Harrison Design and I find it does work for making a slight radius primary cut and the secondary cut on the sear.

Shootist007

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Join date : 2023-10-21
Location : Alabama

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