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Gas Ram To coil Spring Considerations

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Ronno6:
It appears that replacing the Reaxix gas rem in my Umarex Octane is not currently possible.
I need to understand the design considerations of converting to a coil spring powerplant.

The Reaxis ram is 18mm OD and the fully extended length is 330mm.
The rod is 150mm long,and has an available stroke length of 137mm.
When installed, the ran had very minimal preload from what I can tell.

The ID of the spring tube (then wall metal tube inside the piston) is a tad over 20mm.
I understand that a coil spring will increase in OD as it is compressed.

If I consider using a coil spring, how would I translate these dimensions??
I would think that a coil would require about 3" of preload in round numbers, without giving consideration to the spring rate and actual preload required.
That's gettng on up to a spring of just over 400mm in free length.
I am not finding that anywhere.....

So, I have to believe that a combination of spring length and a suitable spacer to make up the difference is required?

As there is so much that I do not (currently) know, what other considerations will factor in??

Ronno6:
If I cannot find a single spring long enough, can I stack 2 shorter ones?

Ronno6:
An engineer at Suspa offered to make one custom for $105.00.......

subscriber:

--- Quote from: Ronno6 on September 22, 2022, 08:26:32 PM ---An engineer at Suspa offered to make one custom for $105.00.......

--- End quote ---

I hope he understands that your application needs the gas spring to be undamped.

How much to have a custom coil spring made?    McMaster has a wide range of parts and materials, but often at double the best price.  They can ship you a custom made steel spring, but probably at twice the price of that gas spring - assuming the gas spring meets your requirements:  https://www.mcmaster.com/coil-springs/spring-type~compression/made-to-order-compression-springs/

I have to believe that there is coil spring stock that can be cut to your required length.  This link takes you to 3/4" OD spring stock (because that seems most common for airgun steel springs, near the 18 mm gas spring body you mentioned).  You can step back and select whatever OD you want from the dropdown menu:  https://www.mcmaster.com/spring-stock/od~3-4/

You should know the installed and compressed length (and the spring rate you are trying to achieve); so there are a few ways to approach this:  https://www.mcmaster.com/spring-stock/maximum-load~range~~-5637010442429/


It may be that the ID is the most important diameter to fit (a non-existent guide?).  Or the OD needs to be a slip fit in the piston ID when the spring is compressed.  What spring OD/ID/wire diameter combinations are available may dictate your choices.  A spring manufacturer no doubt would have more options.

Ronno6:
As a mechanical buyer for 25+ years I have purchased many made-to-print springs of many different types.
I am (well, used to be) familiar with spring design parameters.
Material is something which I have not seen mentioned.
Music wire?
Chrome vanadium?
Chrome silicon?
Valve spring wire?

I used to know people at many spring manufacturers, but, as I retired 18 years ago, they are probably gone now...

Yes, the app engineer and I discussed the need for no internal damping.....that feature would preclude the use of any of their stock gas springs.

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