Canadian Airgun Forum

Came across this when learning about tuning hammer spring in my new PCP. I can see the point of hammer bouncing and sling shot hammer. But isn't it the same as having a short hammer spring? Part of the hammer's travel is unsprung and hence sling shot.

-TL

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I would have thought, without constant pressure against the hammer, there would ALWAYS be hammer bounce, ie: double tap wasting air.

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Best Wishes
Daryl

Mass (hammer) contacting spring, you have resonance system, and hence bouncing. The hammer's mass and the spring's Hook's constant determine the resonance, or oscillation, frequency. The bouncing, or oscillation, will last till the energy is dissipated by loss.

The unsprung travel of the hammer provides time for the hammer to lose its kinetic energy before it gets pushed back to hit the valve stem again. The way I see it, it is important to include damping, or loss, in the system.

I will start tinkering when I receive the replacement hammer spring. I will cut it shorter to let the hammer unsprung. And I will experiment with damping material.

-TL

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The term "sling-shot hammer" was coined when my design for the SSG (stopping spring guide) was "borrowed" and turned into a commercial product (without my permission).... A simpler version uses a short, but stiffer spring to accomplish the same hammer energy, and has become known as the SSS (short, stiff spring).... The SSS requires more cocking force than a conventionally sprung hammer, because it has to get the hammer energy in a shorter distance, and the energy comes from average spring force times distance travelled while being propelled by the hammer.... By definition, an SSS has zero compression when the hammer is uncocked, to it must take more force to compress it when cocked.... It works almost as well as the SSG, but is harder to cock than a conventional (preloaded) hammer spring.... There are many variations of the SSG, here is the original one....



The SSG is preloaded when against the stop on the guide.... Therefore, for the same average force and hammer travel distance, it can require less force to cock it.... the best of both worlds.... A properly designed SSG will use a longer, weaker spring, preloaded against the stop on the guide, a relative long cocking distance, and the hammer will be in free flight for a short distance before hitting the valve stem.... When the hammer rebounds (thrown back by the closing valve), it meets a stationary spring that is already preloaded, and hence more difficult to recompress than an SSS.... The SSS can work OK, at the disadvantage of being harder to cock.... The SSG, when properly built, can eliminate hammer bounce (and the associated wasted air), and actually be easier to cock as well....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Thanks. The SSS configuration is exactly what I have in mind. I think it will work when set up correctly. I quite like its simplicity.

-TL

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What do you think about increasing the hammer weight and adding damping materials between the spring and hammer?

Heavy hammer doesn't help reduce bouncing per se, but it slows down the hammer without reducing its kinetic energy. It lengthens the dwell time. It opens the door to using a weaker hammer spring.

Mass and spring have little loss. The system is under damped. Oscillation dies down slowly. Best is to have the system critically damped. My idea is to insert lossy material, rubber, neoprene etc, between the hammer spring and hammer. When the hammer is cocked, the damper is bottomed out (fully compressed) so that little or no energy is lost when fired. When the hammer is pushed back by the valve return spring, the damper compresses to absorb the hammer's energy.

-TL

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Damping materials have been tried, but I don't know of any that have been particularly successful.... Perhaps they have been installed between the hammer and valve stem, which as you say is the wrong place....

If you venture into bigger calibers, where cocking force is a significant problem, the extra force required with an SSS becomes problematic.... Of course you can use a partially balanced valve to overcome that.... My experience has been that the SSS can still produce hammer bounce that can be eliminated with the SSG.... However, a properly tuned SSS is a huge improvement over a preload spring.... The worst situation is a spring with little preload (ie barely compressed when the gun is uncocked).... It can empty reservoirs by achieving a machine-gun like effect....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Bobs SSG works great...simple and easy to implement, but it's not the same as the Harper Slingshot hammer which is patented and used by Daystate. (At least it used to be...dunno if they still use it.)

Same goal of eliminating striker bounce, different execution.

https://daystate.com/daystate-technology/

https://diffcal.blogspot.com/2015/12/da ... n-air.html

https://www.airgunmagazine.co.uk/featur ... hot-valve/

Al

1500 pound sterling for a air rifle? It'd better be good.

I have seen a few designs. They are basically different renditions of the same concept; unsprung travel of the hammer. I'm gathering materials to tinker. My new airacuda max came with an over-powered hammer spring. It is already maxing out MV and bouncing when set to minimum tension. When the new hammer spring arrives from the far east, I will start monkeying. Will see how far I will go. My primary goal is to have more shots per fill. Hand pumping is good for health. But 5 pumps for each shot is a bit lame. I want to cut it down to 4, or even 3, without sacrificing MV of course.

Thank you guys.

-TL

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Tks for those links, Al. I now understand these mechanisms.

_________________
Best Wishes
Daryl

Finally got the spare springs.

The stock hammer spring has 1.2mm wire diameter. I ordered a stronger one of 1.4mm. Cut it shorter so that the hammer has a few mm of unsprung travel even with 1mm thick neoprene added as damper. Now the uncocked hammer rattle slightly in the assembled gun. Dry firing sounds the same. Will see how it works at the range tomorrow. It is a poor man's sling shot hammer alright.

With the stronger spring, cocking the gun is still quite agreeable.

-TL

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