I made a separate model of the different components and their relationship based on a photograph over which I traced the contours.
I will try to give you the short version of the problem. I have the traced version with my homemade hammer on top. This shows the problem that I was experiencing. After the hammer is re-cocked by the blowback action, the trigger moves forward when released but the secondary sear doesn’t reset the way it should and stays hooked under the lip of the primary sear. Pulling on the trigger again will just make the secondary seal slide under the primary as in safe mode.
The next few pictures show my workaround to use my “NOT” perfect hammer so I could enjoy shooting the 451 until I could solve the issue (if I was ever able to).
This problem continued to nag me and I spent a fair amount of time spinning it in my head until I realized that even if my geometry was closer to the original on my second hammer than on my first one, I had introduced a critical change.
To verify my assumption, I made another file with pivot pin positions taken from the right receiver.
This allowed me to confirm my suspicion. The teeth on the original have sharp internal corners but my waterjet part has relief holes at their roots. This was probably sufficient to modify the dipping angle of the sear thus causing the binding. This picture depicts the effect and we can see the corner of the sear entering the relief hole.
Once I realized that, I decided to give the waterjet option another chance and just made small modifications to my model. Adding a cylindrical boss opposite to the relief hole should control the top surface of the sear and prevent the tip of entering it. Most importantly the angle of the teeth should be adjusted to exactly position the sear where it would give the clearance needed by the secondary sear. The computer assembly was very helpful in doing that.
This picture shows clearly now that under spring pressure the secondary sear has enough room to be able to move up to contact the spring pin of the hammer.
As depicted in the following image, we can see that the secondary sear is reset and the pistol is ready to shoot.
The whole sequence of events is as follows:
The pistol is cocked and ready to shoot.
The trigger is pulled making the secondary sear slide on the hammer pin and pushing on the primary sear block.
At the same time the hammer is free to move forward to hit the firing pin. The hammer pushes down on the secondary sear and provides some room for the primary sear reset…
…which occurs when the gas release activates the blowback action that recocks the hammer. We can see that the primary sear has rotated to engage the notch of the hammer and is in the recess of the secondary sear.
When the trigger is released the secondary sear moves forward enough to clear the primary sear corner …
… to move up to its reset position ready for another shot.
Et voilà! That was easy.
The computer file is sent for another passage in the waterjet cutter for the third version of the hammer.
I think that with this improved geometry it might be possible to use it as a template for a handmade hammer if it is a last resort. Anyway the picture is there and the scale reference accompanies it. Feel free to join the fun.
For my third hammer iteration I decided to include a primary sear too. This is the 2 piece model I made so it would fit on the same ¼” stock as the hammer core.
This is what it looks like after being outlined by the waterjet cutter.
Here we see the 2 parts separated from the main plate of steel. The hole is already drilled in the piece that will become the sear boss and the recess to accommodate it still needs to be shaped on the main body with a fine file. The main body must be drilled so a spring pin could join both components.
This shows the components of the hammer pinned together before being filed.
The fit is better than on the previous waterjet hammer and will require a bit less work.
The hammer and sear ready to be tested for fit in the pistol frame before reassembly.
The verification with the original sear seemed to work correctly but I didn’t reassemble the pistol to shoot it to confirm that. I also made the fit verification with my waterjet sear which needed a bit of adjustment. My boss plate being a bit thicker I shaped it until it didn’t interfere (we can see the slightly curved surface). Since it was cut from a .250” plate the sides had to be shaved down to about .235”, that way I was ensuring that it could slide between the sides of the secondary sear.
In the next installment: Finally, a working 451…