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  • springs

    I've been making this thingy for the past 6 months. when it is finished it will be a moving sculpture

    The extension springs you can see holding the chain are not strong enough. I bought some shorter fatter ones but could not stretch them enough.
    Is there a reference anywhere that will tell me the origional length and the allowable stretch.
    I imagine that this is quite a complicated subject

  • #2
    Try Googling - spring calculator



    • #3
      It appears you have spent considerable time building this "Thingy".

      Could you elaborate a bit more of what it will do, where it would be used or demonstrated?

      An interesting build.


      • #4

        David Merrill


        • #5
          The best I've learned to use is LesjŲfors AB who manufacturs springs, if they don't have it you don't need it Chek their website dfor technical information, as what you are asking depends on the material and dimensions of the spring elements.
          Amount of experience is in direct proportion to the value of broken equipment.


          • #6


            • #7
              Is it that the replacement springs you got don't have sufficient travel or are they just to short. If it's the latter, you could probably just add a link of some sort to make up the length.


              • #8
                I think you are using the wrong design approach. If I understand your set-up, what you need to do is to set the proper tension in the chain which is being used to drive something. In other words, you need enough tension to keep it on the various sprockets. What you have is a fixed length chain and a fixed distance that the spring must fit in. This would require an accurate calculation of the spring's properties in order to work and if anything in the system changes, including the spring aging, then it will no longer work.

                A more common arrangement for systems like this is to use a spring that is heavier than needed and an adjustment screw on the end to adjust the tension. The spring is installed with little or no tension and the screw is tightened (with a nut) to bring the tension to the desired value. Such an adjustment should hold for a long time but when needed it can be readjusted to keep things working properly.

                It looks like this:

                Chain - spring - threaded rod - rod passes through hole in bracket - adjusting nut on far side of bracket - and finally a lock nut to prevent loosening
                Paul A.

                Make it fit.
                You can't win and there is a penalty for trying!


                • #9
                  Looks to me like a trampoline spring would be just about right for that. Lots of those get tossed every year.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                  • #10
                    Look at the auto parts store, in the Help! section, iirc. They sell a pack of 4 springs of various rates, with hooks on one end, and very long straight 'stems' on the other, that can be cut and bent at any length you need.
                    Definition: Racecar - a device that turns money into noise.


                    • #11
                      Near as I can tell this does the same thing except the cam follower travel should be reduced by 1/2. It's a lot simpler.

                      Just put a coil spring on the cam follower to return it.
                      Last edited by Evan; 04-21-2012, 08:56 PM.
                      Free software for calculating bolt circles and similar: Click Here


                      • #12
                        an explanation

                        Firstly thanks to every one who replied
                        As sasquatch sugests it would help if I supplied more detail

                        At the end of each arm is a shaft with a sprocket fixed to it

                        On the front end of the shaft is a figure with a cup in an outstretched arm represented here by an allen key

                        At the top will be a teapot with water pouring out of the spout. The figure has to remain in a vertical position as it moves anticlockwise following the arc of water.

                        At 12 oclock the figure is still vertical
                        At 11oclock the figure begins to fall in a clockwise direction in relation to the arm

                        By 9 oclock the figure is head down.
                        The lower half of the cycle is screened by a cloud with a group of people underneath
                        All the movement of the figures is controlled by the central stationary cam
                        The thingy is suposed to represent random good fortune(an individual plucked from the crowd, raised up to receive a blessing. Unfortunately the blessing is short lived and worse the tea(blessing) falls on the crowd below adding to their misery. See what happens when they change your pills!!
                        Paul, your suggestion is exactly what I was looking for.
                        Evan, I can see your design change would work if the sprocket on the end of the pushrod was fixed. Is that what you had in mind?
                        Thankyou again everybody for you help


                        • #13
                          Yes, but you don't need a sprocket at all. Just fasten the cam follower to the chain. Although the path is slightly angled there will be enough slack in the chain to allow for that easily.

                          Or, you can do without the outer cam follower support and allow the bottom one to rotate a little on just one bolt so that it will swing slightly to follow the chain. It will still follow the cam just fine. A compression coil spring can be placed at the follower end of the cam follower shaft. You don't even need to make any changes to the construction, just reroute the chain and lose three sprockets. It also hides the chain a little better.

                          The best way to make a follower for that type of action is to route a groove in the cam with a ball bearing as a follower. That way the follower is trapped in both directions and no springs are required.
                          Free software for calculating bolt circles and similar: Click Here


                          • #14
                            Dave, it's simpler than you think.....

                            There are all kinds of formulas etc out there but to cut to the chase on an expension spring you want to select on where the extension on it will be approximately 1/3 of the closed lenght. Select a wire gage that will provide the tension you need. If you're stuck finding one that is long enough there is no reason that you can't use several in series to get the length of travel you need and still have it fall in the stretched lenght you need.

                            And if you really want to be a dangerous guy just take music wire and wind the lenth of spring you need. It's not rocket science but there are some trick to it. If you're interested in more info just drop me an email.
                            Allans Rule: Anything worth doing is going to be a pain in the butt.