Crosman 451 Hammer saga: Part 2

I went to my friend’s place to use his metal band saw to roughly cut the shape.

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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 plasticine.

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

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In this picture, you can see the layers and you will also notice the finish which is a bit crude. 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 but the lowest portion around the pivot hole must be reduced from .250” to .235”.

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The next critical stage will be to put everything together and in working order.

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For the reassembly procedure I used the same pictures as the disassembly. The next image is the Crosman 451 with my homemade hammer ready to be tested.

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Unfortunately, after installing a CO2 cartridge, loading the pistol, pulling the hammer and taking a first shot that recocked it as it should, the trigger was not responding.

The feeling was the same as if it was in safe mode or in the half cock position.

Something was wrong but what?

When I compared the original with my hammer, they seemed very close. Since I took the measurement by hand with a caliper it is not top notch accuracy.

Because I was returning to work, I decided on another approach to improve the quality of my model.

After scanning the original hammer, in Adobe Illustrator, I traced over the picture to obtain vector lines that can be transferred to my CAD software.

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Since, this time, the plan was to take advantage of a machine available at work, my model is a bit different than the first one.

It will continue to be a contour approach the same as the first iteration but it should be more precise than my hack job on the band saw.

The machine that will shape the contour sent from the CAD software is a waterjet cutter. It used high pressure water mixed with some fine grit to cut through the steel as if it was butter.

Fabricating the hammer on a CNC mill would be more accurate than what can be obtained with the waterjet cutter but it would also require a lot more preparation work.

What I mean is to be able to shape the metal, the mill has to push the cutting bit against the stock. That push requires the part to be solidly fixed to avoid any movement. Since the hammer is fairly small, holding it in place would be a challenge. Because it would be a single solid piece, both sides would need to be machined. Furthermore the teeth being very small, a very small cutter must be used and normally small cutters are also very short. This means that the teeth of the hammer would be shaped from both sides. Maintaining proper alignment for two setups is difficult. Making a jig is practically an obligation and this represents additional work and expenses. In a production situation it is justified by the number of repetition. What I am doing is one of a kind and the reason why I want to stay away from that option if I can.

This is the new model from which the contour will be exported to the waterjet cutter software. Preparing the cutting guide is fairly quick and, once the machine it set and ready to go, the actual cutting is very quick too.

Most of the time, we are using that machine to prepare big chunks of material to a rough shape that will be completed on a mill for the finished cut. This provides the best mix of time saving and accuracy.

In my case I am trying to get my final product directly from the waterjet with minimal hand finish (or at least a lot less than my first try). It is an experiment for me because with this small part I am flirting with the limits of what is achievable.

The diameter of the jet is .040” so having sharp internal corners is not possible. The jet cannot cut perpendicular all the way through so the walls have a very slight taper. Since, at ¼”, my part is not very thick I guess that it would not be an issue. I also included some serration on the tip of the hammer head region and to minimize fitting, I also added 2 relief arcs at the root of the teeth.

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This is the result obtained from the CAD file. To prevent the small parts from falling into the tank a holding tab is left in an area where it is easy to file it off. Here we can see the 2 small pieces for thickening the head already cut off from the 1/8” stock and the hammer core still in place on the ¼” stock. They can be removed from the main plate either with a hacksaw or a dremel tool with a cutting disk. We can see that the serration disappeared in the process. My geometry was probably too small for the .040” diameter jet.

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Since the guide lines were extracted from the same model, I was expecting the result to be a fairly close match. I am not sure what happened because after I cleaned up the holes in the parts and assembled them together I discovered that I would have a lot more filing and sanding than initially expected.

After talking to my friend who cut the part for me, it seems that possibly the pieces have slightly moved under the waterjet pressure. Anyway this is not in a very critical area and consequently I could easily live with it.

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For comparison, I decided to weigh the different hammers. This is the original and the lightest. Sintered steel is metal powder compacted in a mold and heated. I guess the material is porous making it less dense than the one made from steel plates.

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This one is the handmade hammer and is the heaviest.

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The one cut on the waterjet is lighter than the handmade one probably due to the quantity of material removed to bring the surfaces at the same level.

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This is a comparison of the original hammer and the waterjet hammer both at full cock position and they look about the same. I hope that this hammer will work correctly, I will know for sure only after it is reassembled.

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Before putting the pistol back together I took the opportunity to disassemble it one step further in order to get the dimensions of the primary and secondary sears. For doing this kind of job it would have been very nice to have two pistols, one collectible to store away and one beater to experiment on.

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Unfortunately, after reassembly and a shooting test, I obtained exactly the same result as with my first hammer. What a downer!

Back to the computer and the CAD program to try to make sense of the trigger mechanism.

R-Gun Pete

Related Pages

Crosman 451 Hammer saga: Part 1

Crosman 451 Hammer saga: Part 3

Crosman 451 Hammer saga: Part 4

Crosman 451 Hammer Saga: Part 5

Crosman 451 Hammer saga: Part 6

Crosman 451 Hammer saga: Part 7

Crosman 451 Hammer saga: Part 8

Crosman 451 review

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