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PostPosted: Sat Aug 27, 2016 2:18 pm 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
My other thread on making a new hammer for the Crosman 451 is pictures heavy so I decided to start another thread for the trigger system exploration.

topic73597.html

I want to understand how it is working in order to solve the issue that I have with my hand made hammer prototype. The pistol recocks as it should after the blowback, but the trigger offer no resistance (similar to when it is in safe mode). The hammer has to be slightly pull back from the cocked position, after that, the trigger offer some resistance and it can be fired normally.

I started by using a picture of the internal to sketch the shape and relations of the different components in Adobe Illustrator and save as a .dwg file.

Image

Because the picture is in perspective the actual positions cannot be accurately translated so again it is an approximation. Hopefully it is enough to make sense of the sequence of events.

This file was then transfered in my CAD program and transformed into part models that were assembled together.

Unfortunately, I couldn't make it works as a mechanism so I moved it by hand and studied the relations to try to understand what is going on.

From those different positions I took screen shots to build a sequence of pictures.

This is the result.

R-Gun Pete

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PostPosted: Sun Aug 28, 2016 2:40 pm 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Something was still bothering me. I was not completely satisfied of the explanations for the release portion show in the previous series of images. The way it was depicted, I thought the secondary seal was travelling downward as well as applying sideway pressure on the seal. The problem is that it would lack strength to push it out of the way.


This series of images shown in the following picture has been made with repositioned pivot pins for the hammer and the sear. It is not that much but enough now to understand better the relations between components and what should happen at the moment of release. The movement is directly transfered from the trigger in a sideway direction that will force the sear to rotate until the cocking teeth are clear of any obstruction leading to the hammer hitting the firing pin.


Image



Now this knowledge should be applied to understand what is wrong with my homemade hammer.


To my trigger assembly study file, I added the hammer part I made a few days ago. It seems really bad when overlapped over the hammer which was traced from the picture but it is probably not dramatic as it appears. My hammer had been compared with the actual hammer during fabrication and it was fairly close. The hole for the spring pin at the top of the hammer (traced from the photo) is probably more innacurate than mine due to the perspective effect.


This being said, on my hammer, I just used the contacting pin for the secondary seal and used the teeth for the sear contacting angle. This what enough to point me in the right direction to understand what needs to be improved on my hammer design.


In Comparison 1, we can see that after being recocked by the blowback the secondary seal notch has one corner hooked underneath the surface of the boss of the sear. This will lead to the surface sliding on the other one without resistance. This means the trigger will move freely as it it was in safe mode.


Image


In Comparison 2, the hammer is pulled back and the rear corner pushes on the sear to rotate it down a bit further at the same time that the pin tangent to the top of the secondary seal lets it go up just a bit. This brings the boss of the sear lower than the notch.


Image


In Comparison 3, we can see that when the hammer is released it returns to the cocked position with the boss of the sear in contact with the side of the secondary sear below the notch. The trigger offers now some resistance and if pulled it will fire the pistol.


Image


I have now the why, what is left is to redesign a new hammer that will work properly. My intent is to get a 3D scan of the original hammer and overlap my part over it to rectify the geometry.


The plan for the next iteration would be to have the shape cut with a waterjet cutter. This will require a bit of manual finishing but would be a lot better than my first experimentation.


I will post the result when I have a chance to complete the second version and try it.


R-Gun Pete


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PostPosted: Sun Sep 04, 2016 2:24 pm 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
After making a second hammer for the 451 and obtaining the same result as the first one, I am now ready to update my post with new informations.

This second hammer was made from a new CAD file which has the geometry, built from scratch, based on a scan of the original hammer.

It also has been cut with a waterjet cutter assuming that it would be more accurate than me cutting the shape on a band saw.

Before reassembly, I checked the action with the springs removed to avoid any "Jack in the box" effect. Both versions seemed to be doing what needed to be done.

Original neutral

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Waterjet neutral

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Original half cock

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Waterjet half cock

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Original full cock

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Waterjet full cock

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After reassembly and a shooting test, I had the same problem as with my first hammer. The hammer is recocked by the blowback but the trigger stays disconnected as in safe mode.

The hammer only needs to be thumbed back a tiny bit to feel the reset and made the trigger ready to shoot. My geometry is getting really close to what it should be but no cigar yet.

I thought that maybe the slide was not pushing the hammer far enough so I made a shim.

Recocking shim

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Recocking shim on pistol

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This was not it because the same problem was still there, so I thought that maybe the spring for the secondary seal was not strong enough to push it up. I added another spring in the grip to test my hypothesis.

Extra spring for secondary sear

Image

It didn't work either.

I scratched my head and looked at the action moving through the space in the handle. When it is cocked by hand from neutral the trigger is always alive but when it is cocked from the blowback it isn't. The only difference is that the trigger is pulled back when recocked by the blowback action. I was able to mimic what was happening by cocking the hammer while pulling the trigger. In that case the secondary link stays down instead of moving up (which replicate what I was experiencing when shooting with CO2 in the pistol).

I decided to go back to the computer and see the different stages of the cycle.

This time I think I found where is the problem.

Stage 1

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Stage 2

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Stage 3

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Stage 4

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Stage 5

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Stage 6

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When comparing the original hammer with mine (see comparison pictures earlier in the post) the space on the left of the tooth of the full cock notch is flatter than on the other (mine was rounded when I filed the contour by hand). This is probably the surface pushing the sear out of the way of the secondary sear at the end of the blowback path.

All the time, I was concentrating on the location of the teeth in relation to the pin that pushes on the secondary sear, but I was not paying close attention to this region as I didn't realize that it could be important.

I will probably try to machine the next one so the geometry from the CAD is not distorted by any manual operation.

It might be a little while before I can obtain new result but if I am successful, I will update the post.

R-Gun Pete


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PostPosted: Sat Jul 28, 2018 6:30 pm 
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Joined: Sat Jul 28, 2018 6:26 pm
Posts: 1
I don't see diagrams of the hammer safety disarming trigger function - has that been a factor?


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PostPosted: Sat Jul 28, 2018 7:06 pm 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Hi Duct Taped Goat.

The 451 has no conventional safety switch, it uses the first notch on the hammer as as safety, the same on Colt SA revolver.

This was a work in progress and some of the iterations made later solved my problem.

R-Gun Pete


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PostPosted: Mon Aug 13, 2018 5:18 pm 
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Joined: Thu Mar 22, 2007 6:29 am
Posts: 342
Location: niagara
Wow that’s some great info right there. I wish I had one. They are hard to find nowadays


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