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Making a new hammer for a Crosman 451
https://www.airgunforum.ca/forums/topic73597.html
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Author:  R-Gun Pete [ Fri Aug 26, 2016 12:24 am ]
Post subject:  Making a new hammer for a Crosman 451

After looking everywhere for the Crosman 452 Factory Service Manual, I finally discovered that Mr Marvin had it. He graciously provided a copy to me.

Armed with that information, my goal was to disassemble the pistol to get the hammer out in order to measure it and make a new one before the original was broken.

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This is a weakness of the Model 451 because the hammer is made from sintered steel which is very hard and brittle.

I had only a few days of vacation left and I wanted to get it done before returning to work.

I spent some time reading the manual and trying to relate the parts with the diagram.

The exploded view is a bit confusing and trying to find the parts number ia a pain. So I ended up color coding the different groups.

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Before starting the dissassembly, the CO2 cartridge should be removed , then the grip. By removing the pin the goes through the sight, the slide is unlocked and can be removed after unhooking the spring.

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Both heavy springs on each side of the hammer must be released. The piercing nut is backed off completely and the piercing lever and its screw are removed.

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After removing the screws of the receiver, the right side panel is lifted off. Be careful as there is a spring attached to the front and it must be unhooked.

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At this point, the internal components were exposed and luckily nothing popped out. I took a good reference picture to help me put backthe parts together later.

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I removed the spring of the secondary sear to relieve some pressure and I was able to get out the hammer group without too much difficulty.

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The big pin hold the group together and after sliding it out I isolated the hammer (that was my initial target).

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At home, my equipment is fairly limited (hacksaw, jigsaw, drill press and files) but I didn't want to wait until returning to work to tackle the project. Looking at the hammer, we can see that it is not very complex.

Basically the central portion which is 1/4 inch has all the critical features and the hammer head which is thicker is only to provided weight for the impact.

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If I isolate the central plate, it becomes only a 2D cutout which is simple and I can also have 2 simple pieces to attach each side to fatten the head.

The trickiest portion was to measure the hammer because it is 3D but eventually I got it and made a computer model. Because I would make it by hand, I just printed the shape at the actual scale.

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I had some scrap of steel but only 1/8 inch. It worked, it just meant that the core would be made of 2 plates. In the picture, we can see the original, sample of the scrap metal and the prepared part with the paper guide glued to it.

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Because the 2 plates and the paper were held together with double face tape, the first step was to drill some holes and insert pins so nothing would move.

Finally to cut the shape, I gave up on the idea of using my hacksaw and I went to my friend place. He has a metal cutting bandsaw.

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Back to my place, it was time to fine tune the contour with files. I worked mostly with my paper guide but just to be able to compare more directly with the original, I made an imprint in playdo.

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My homemade hammer doesn't fit perfectly in it but the critical areas are close enough.

In this picture, we could see the layers, also notice the finish. When I reached the end I didn't have any patience to do a nice sanding job and I wanted to test it as soon as possible.

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The new hammer fits perfectly in the hammer group assembly. The critical step will be to put everything together and in working order.

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The reassembly was a bit difficult but eventually I was able to complete it.

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I charged the pistol with CO2 and BAM, it worked. The blowback recocked the gun.

A bit of deception. It looks like it is recocked but the trigger doesn't work. It seems to think that it is at halfcock. Pulling back on the hammerjust a bit and pressing the trigger makes it work.

After several shots that way, I got a string that worked correctly but randomly I could get some that didn't.

Toward the end it seems to be working better. Maybe it needs a break in period.

Anyway, I will do more tests.

So if you are a 451 owner, this might be an option. For me, I know that I will be able to enjoy mine without worry and if, later, I decide to sell it is always possible to put back the original hammer.

R-Gun Pete

Author:  R-Gun Pete [ Fri Aug 26, 2016 9:49 am ]
Post subject:  Re: Making a new hammer for a Crosman 451

I did more test this morning (this time actually shooting pellets).

I still have the same problem a yesterday where the pistol will cock but stay in safe mode (trigger moving without resistance).

Just pulling the hammer a bit further back and releasing it deactivate the safe mode (which normally should be at the half cock position), then it can be shot.

It is a bit annoying but doesn't handicap too much the shooting. Being held in a two hand grip, when the hammer is cocked it can simply be flicked by the thumb of the supporting hand and shooting is resume fairly quickly.

I ended up getting one full mag more than with the original (7 mags vs 6) so maybe my weight is slightly different.

Basically, I will have to look at the geometry of my hammer as at this point I am not too sure where is the problem.

Anyway, I forgot to include the drawing I used to make my part.

it is the first version and might be updated once I figure what is the problem.

It could be with the placement of the features on my CAD model but it can also be the fact that my hammer is hand made.

R-Gun Pete

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Author:  wllm995 [ Fri Aug 26, 2016 11:57 am ]
Post subject:  Re: Making a new hammer for a Crosman 451

Fascinating stuff!

FYI:

http://co2airguns.net/Collection/Crosma ... /index.htm

For those that may not be familiar with this Classic Crosman.

8)

Author:  ColdAir [ Fri Aug 26, 2016 10:14 pm ]
Post subject:  Re: Making a new hammer for a Crosman 451

R-Gun Pete,

Another great project and interesting read.

Nice work.

Author:  R-Gun Pete [ Sat Aug 27, 2016 2:23 pm ]
Post subject:  Re: Making a new hammer for a Crosman 451

Hi wllm995 and ColdAir!

Thanks for the comments.

I was busy trying to figure out what is the problem with my hand made hammer. It could be just a matter of tolerances or my geometry is not completely righty.

Because this thread is very pictures heavy I decide to start a different one for the trigger system exploration.

This is the link.

topic73616.html

R-Gun Pete

Author:  R-Gun Pete [ Sun Sep 04, 2016 2:04 pm ]
Post subject:  Re: Making a new hammer for a Crosman 451

I made a new version of the hammer. This time it was traced over the scan of the original. Hopefully the dimensions will be closer than the model I made for my first hand made iteration.

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Also I was planning to have my components cut by a waterjet machine, I was guessing that it would be more accurate than when I cut my first version on a band saw.

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Normally, the waterjet cutter is used to rough cut the stock for a job with the intent of minimizing the machining time for the final shape. In this case, I was hoping to use the parts directly with minimal adjustments. Since the guide lines were extracted from the same model, I was expecting the result to be a fairly close match.

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I discovered that for small parts the tolerance variation could be very noticeable depending of the orientation of the shape on the machine when it was cut. It turn out that I had a lot more filing work than I initially expected.

To compare the weight of the original and the ones I made, a small scale was used.

Weight of original

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Weight of handmade hammer

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Weight of waterjet hammer

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It seems that the sintered steel is a bit lighter. This is probably due to the fact that the material is porous. The other ones have different weights because the CAD geometry is slightly modified (as well as being shaped by hand which can cause a larger difference).

Before reassembly, I verified how the original hammer and waterjet hammer compared to each other when at the fully cocked position. The springs were removed to be able to observe what was going on without risking that the parts would jump out of the frame.

Original fully cocked

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Waterjet fully cocked

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As everything seemed fine, I reassembled the pistol.

Unfortunately, I have the same problem as with my first hammer. The blowback recocks the hammer but the trigger is in safe mode. The hammer has to be thumbed back just a little to reset the link with the trigger in order to shoot it.

This is really annoying because this time the geometry has been taken of from the scan of the original hammer (which I would have expected to be right on).

After doing some research to update my other post on the trigger system exploration, I realized when comparing both pictures of the fully cocked hammer that the area on the left of the tooth is flatter on the original than on mine. When I filed the contour I have smoothed the transition. This surface is probably what cams the sear to its proper position to have the secondary sear reset at the end of the blowback cycle.

I think I am getting closer to the solution and I will need a third iteration to confirm that.

R-Gun Pete

Author:  R-Gun Pete [ Sat Sep 10, 2016 3:44 pm ]
Post subject:  Re: Making a new hammer for a Crosman 451

Today I had some time to investigate what could be wrong with my second hammer.

The plan was to reinstall the original hammer to confirm that the pistol would work flawlessly or not. If it works, this means that my geometry is slightly off somewhere but if I have the same problem with the original hammer it is something with the reassembly that is wrong.

The answer is that my hammer geometry is not bang on and the trigger doesn't reset itself at the end of the cycle.

To review the interaction of the part, and try to find exactly how the faces rub against each other, this time I removed practically everything except the loading system and the valve.


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I measured the sear and the secondary sear and made CAD models of the parts.

I tried to mesure the hole locations for the pivots but it it too difficult to do it on the casting. I think that I will again use a picture of the frame to get started.

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I am not sure when I will have time to continue on the project but if I can refine my hammer geometry the next iteration will be CNC machined to minimized the tolerance deviation.

R-Gun Pete

Author:  R-Gun Pete [ Sat Sep 17, 2016 3:31 pm ]
Post subject:  Re: Making a new hammer for a Crosman 451

451 hammer -last post for CAF

The last time I updated my post, I thought that I would have to machine a new hammer on the CNC mill. No doubt that the end result would have been more precise than what I did until now but this meant that I would have to plan a jig to allow 2 setups because the part would require machining on 2 faces. Holding small parts is always a challenge. Furthermore to obtain the details of the teeth, relief holes and a small endmill (1/16") would be necessary. This represent a fair amount of preparation work so I decided to give another chance to the waterjet cutter.

After analyzing the problem (the trigger not resetting after the blowback recocking of the hammer), I realized that the sear was not tilting far enough to allow the secondary sear to slide in front when the trigger was released. This tilt is controlled by the angle of the full cock tooth. My first hammer made by hand had sharp corners but the angle of the contact face was probably just a bitt off. The second was shaped by the waterjet but, because of the radius of the jet, relief holes were added to the corners. The tip of the sear was possibly trying to get in the void thus changing the angle and causing the secondary sear to get hooked underneath.

For my last waterjet try, I modified the geometry in a way that would force the sear face to stay in contact with the face of the teeth by adding bosses on the other side of the relief holes. This effectively changes the angle of the sear and tilt it forward.

Since in my last post I mentioned that I made a CAD model for the sear, I decided to make a new one by adding the geometry beside the hammer core that would be cut in a 1/4" plate.

The sear has different widths that would normally require machining but using the same principle as for the hammer, I was able to make it in 2 parts and pin it together after.

In the following picture we can see the steel stock with sear pieces still attached.

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The following image shows the sear pieces after being cut off from the stock plate. The sear contact plate is shown filed down and drilled. The notch on the sear main body has to be squared and filed smooth. After that, the plate would be attached with double face tape (to position it correctly) and a hole would be drilled in the main body guided by the hole in the plate.

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Here we see the hammer assembled with spring pins. It is shown from two different angles before contour filing.

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It could be noticed that the fit is a lot better that the previous time. My friend thinks that the part possibly shifted because the clamps were not tight enough. Anyway I am happier because it required less work to shape it this time.

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The hammer and sear are ready to be tested. In the next picture, the details of the teeth can be seen and the sear is assembled with the spring pin. After working the trigger mechanism with the original sear and the new sear the problem seems to be solved but the original worked a bit better than mine. The angle of the sear is definitely improved when sitting in the full cock notch so the secondary sear just slide in front of it as it should but, with mine, it gets sometimes stuck underneath.

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The next photo shows sears comparison. The original sear is on the left and mine, on the right, is spring pinned. The plate has been filed a bit to give it a slightly curved face and the width of the main body has been reduced from .250" to .235" (that is the width of the original). Those adjustments were enough to make it works reliably.

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Finally in this last picture, there is the whole series of hammers. From left to right, there is the original, the handmade hammer (4 plates of 1/8"), the first waterjet version and the second (both have a core that is 1/4" and head plates that are 1/8"), there are also the original sear and the water jet sear.

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This time the pistol is working as it should with my hammer and my sear. I can get six shots in semi automatique mode without any pause as it was intended to shoot.

Now I don't have to worry about shooting the Crosman 451 as much as I want. The original hammer and sear are safely tucked away and preserved intact if I ever decide to sell it.

Mission accomplished, my brain can stop being in problem solving mode and I will be able to relax and just enjoy it.

R-Gun Pete

Author:  DerekVinyard [ Sat Sep 17, 2016 4:53 pm ]
Post subject:  Re: Making a new hammer for a Crosman 451

Amazing work with the equipment you have access to. If you have scaled drawings, I can CNC the parts for you free of charge. Just PM me...

Michael

Author:  R-Gun Pete [ Sat Sep 17, 2016 6:40 pm ]
Post subject:  Re: Making a new hammer for a Crosman 451

DerekVinyard wrote:
Amazing work with the equipment you have access to. If you have scaled drawings, I can CNC the parts for you free of charge. Just PM me...

Michael



Hi Michael!

It is not that I cannot CNC the parts myself, it is just that I am a bit lazy.

For a production run it is worthwhile, for single part it depends.

It is just that I came across some articles some time ago and they were discussing manufacturing. There was the case of a trigger which was made of stamped sheet metal stacked together. This where I got the idea of doing my parts in layers. Each of the them is a single 2D contour but when bunched together it is a 3D object.

The other thing is that I can get access to the CNC mill when there is no job planned for it (so that is great now but in a couple of years I will be retired and without fancy equipment). This is one of the reason that I am experimenting with a cruder approach. I want to know if I am able to fix my stuff myself using basic means.

If you are interested in making CNCed parts for the challenge or maybe to sell (I am not sure how many how many consumers are kicking around), I can provide you a CAD model.

I will have to modify some dimensions to reflect the manual adjustments I made to the flat patterns that used but it should not be a big deal.

You can PM me if you want.

R-Gun Pete

Author:  R-Gun Pete [ Mon Dec 12, 2016 11:23 am ]
Post subject:  Re: Making a new hammer for a Crosman 451

Based on the work in progress that was initially posted on the CAF forum, a series of articles have been reorganized into a single integrated story under the title "Crosman 451 Hammer Saga".

The articles also contain more detailed Disassembly/Reassembly pictures as well as a last portion that was done after successfully repairing my pistol.

The title for that portion was "The Hammer Saga - The last Chapter: leaving no stone unturned" where I was exploring both extremes: I made one hammer in the most artisanal way and another one using a CNC mill.

Those articles were first published on the "Pistol Place" but, unfortunately, before the last installment (CNC Hammer) could be on-line the site was locked by the hosting company and the owner was asked a substantial amount of money to get it going.

Since then, he rebuild a new site (World of Replica Air Pistols) and migrated several of the articles previously published. There is a fair amount of reviews back on-line and the "Hammer Saga" is in progress. Hopefully the last two installments should available soon.

If you are interested in replica pistols, there is a lot of good reading.

This is the link to the main page:

https://worap.wordpress.com/

R-Gun Pete

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