Elastic limit of spring calculator

Discussion in 'Piston & Spring' started by RobF, May 15, 2017.

  1. RobF

    RobF Administrator Staff Member

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  2. matt goodson

    matt goodson New Member

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    I must be dumb because I cant see why.
     
  3. RobF

    RobF Administrator Staff Member

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    Because the elastic limit of most springs small enough in diameter for the pistons is exceeded.
     
  4. DEAN C.

    DEAN C. Steyr Convert

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    Never thought of that regarding airgun springs, but it is obvious when you think of it.
    Anything past its limit of elasticity will not return to its original size or be fatigued.
     
  5. matt goodson

    matt goodson New Member

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    Thanks :) .........
     
  6. hmangphilly

    hmangphilly Floppy Quick Phil

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    Looking like many of them fall into that category ...........that's why they "wear out".........all becomes clear :lev
     
  7. Nick G

    Nick G Active Member

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    When you say wear out do you mean they retain a "set" ie get shorter, go s shaped , or worst of all break .
     
  8. hmangphilly

    hmangphilly Floppy Quick Phil

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    any of the above really Nick .

    the most common thing we see in production guns is the springs eventually taking a set .
    probably due to being compressed beyond their limit.

    all springs will naturally try to buckle , so unless this is controlled then it will happen . fine line here though between allowing it room to expand and room to buckle

    I'm thinking either of these two things will result in stresses that will eventually cause the spring to fail .


    Rob's been crunching some numbers and they are quite an eye opener .

    seems the spring we've been using on a 21 mm tune has been compressed to around 180% of its elastic limit .....no wonder it started to take a set .............

    the previous one got shorter and shorter and we were constantly chasing the power with preload , when in reality the spring was goosed .


    I thought it was just about controlling the shape , i.e buckling but it would appear to have been more than that

    starting to look like there isn't enough spring in a 21 or22 for enough spring without asking it to work too hard .

    looking at the smallest cross section we can use , so 23 is the next round number . .........rob wont let me do 22.5 yet ...........but i might do one any way and not tell him .


    if i find the time, and if any one 's interested I might do a jackanory on one of our drop in , fully reversible reduced bore tunes.

    I t breaks my heart to see all these bits of tube getting glued into comp tubes and then the tube still leaking . I'll see if my mucka is up for it ............
     
    Last edited: May 17, 2017
  9. Nick G

    Nick G Active Member

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    Sounds like you are making a one piece end cap and tube to just screw in , are you making it one piece or welding/screwing the tube on to the cap.
    I looked at the calculator and there is a vortek spring in the usa that looks promising for 22mm .775 od x.118 gauge . If i have used the calculator correctly it gets me very close to the stroke I am using
    Though all this trouble for easier cocking ,I may go back to my 25 mm set ups, they seem to be very reliable .
     
  10. SDplinker

    SDplinker Pellet testing...yawn

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  11. airborn68

    airborn68 Active Member

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    I cant understand why my 22 mm skirted piston running the Hw style seal has not failed yet !!!!! looking at the spring calc.

    Jon
     
  12. hmangphilly

    hmangphilly Floppy Quick Phil

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    hey you're not allowed to guess .
    I told you about it ages ago . :D

    you called it elegant .........remember :)
     
  13. RobF

    RobF Administrator Staff Member

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    Nick,

    Is it this one?

    http://vortekproducts.com/ourstore/airgun Springs/Air-Gun-Springs?product_id=238

    Seems a bit short at 162mm long?

    I'm having trouble seeing a lot of the overal lengths on the Vortek pages.
     
  14. Tench

    Tench WHFTA World Champion 2016.

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    It is just the same in the engine tuning world, make big power and someone will say "that will blow up!" When the reality is if you do your home work and don't exceed the mechanical limits of any of the components and can manage the heat and lubrication then it will be reliable regardless of the bhp/L achieved.
     
  15. Nick G

    Nick G Active Member

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    I do remember now , that was some time ago.
     
  16. Nick G

    Nick G Active Member

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  17. RobF

    RobF Administrator Staff Member

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    maybe...

    I might email vortek and gets some lengths off them... there's a few others that look interesting but lack any length info...
     
  18. 22pelletpete

    22pelletpete New Member

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    I was going to post a tirade regarding my 7 month old £70 vortex kit for my TX 200 ,which is now down to 10 ftlb when I spotted this post,and it all makes sense now.The spring is obviously overstressed,or Ive got a bad un.Only 2 thin pack can be added or it wont cock.I have put the old tx spring back and things are twangy but 11.5 which is what Iwant. The vmac in my 97K is still going strong after 3years, maybe better steel eh?
     
  19. hmangphilly

    hmangphilly Floppy Quick Phil

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    Chasing the diminishing power by adding preload is only a short term fix .
     
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  20. Adam

    Adam Well-Known Member

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    The V-Mach spring in my 97K has been in there nearly 9 years! I replaced the seal 4 years ago with a HW one but that's all I've done to it since putting the kit in.
    Last time I chronoed in Jan it was doing 11.5 ft.lb. They are good quality springs but they are also stiffer (thicker) wire than standard, with very little preload.
     
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