scope expansion

Discussion in 'Competition Forum (All Calibers)' started by Alex Wheeler, Oct 29, 2016.

  1. fredo

    fredo Silver $$ Contributor

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    Even if one were to develop some type of ring/base that could mechanically "relieve" a measurable, yet negligible amount of thermal expansion, how could one isolate that it isn't the scope's internals being subject to the same temperature variation isn't causing POI shift?

    IMHO buying a product on those grounds alone would be akin to devil-woman-pelosi's excuse for passing ACA: "we have to pass it before we actually read it"...

    To add...only a dummy would let their rifle bake in the Sun and not expect something to change.

    Interesting stuff to ponder, no doubt. But from a simplistic perspective, one might surmise that powder temperature stability alone would allow for enough 'noise' on target that it squelches whatever's happening to the metallurgy of the optical system?
     
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  2. JRS

    JRS Silver $$ Contributor

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    Have you ever watched someone camber a steel beam or piece of channel using a torch? In the old days, before the word "camber" became the norm, the process was called heat shrinking, because you are shrinking that area of the web and flange when applying heat. So…. yes, depending upon how and where it is used, heat shrinks.
     
  3. Papa Charlie

    Papa Charlie Silver $$ Contributor

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    Not unusual, the growth of the molecules in the area you were heating were restricted by the molecules that were unaffected by the heat. This affect can cause warpage and excessive stresses to be built up in the metal and in some extreme cases lead to early failure. Stress relieving of metals from machining and heat treating are very common, generally done by heating the part up to a temperature and allowing it to cool slowly. The temperature will vary depending on the metal, mass and other factors.
    Heat in metal is a huge factor when doing precision work. Critical measurements need to be taken at room temperature especially when working with mating surfaces.
     
  4. Papa Charlie

    Papa Charlie Silver $$ Contributor

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    Heat shrinking is not just the process of heating metal to shrink it, is a process of heating metal then cooling it quickly to shrink it.
    The idea is to excite the molecules and cause them to expand and then align themselves in a chain, then by cooling quickly, they are locked into the chain and therefore take up less space causing a shrinking affect.
    Imagine a bunch of balls with excessive space between them, then aligning all those balls in order, they over all affect will be to reduce the volume that they occupy.
    This is done a lot in hot rods and sheet metal work to correct where metal has been stretched, a condition also known as oil canning since they will flex back and forth.
     
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  5. JRS

    JRS Silver $$ Contributor

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    This is an experiment from Epstein. It is an eye opener, and a hole opener:D

    He suggests taking a square piece of metal plate, dividing it with a 3x3 grid into 9 equal smaller squares. Then heat the entire plate. Each of the smaller squares expands. But, if the central square were missing (a hole in the plate) then the same expansion would take place in the other 8 squares leaving a bigger hole. Alternatively, if you heated the entire plate and then removed the central square (hole) at the end after it has expanded, the remaining hole is larger than the original size of the small square:cool:;)

    The mason jar thing works the same way. Run hot water on the lid and the hole expands without growing the OD of the lid.
     
    Last edited: Jan 11, 2018
  6. 308sawyer

    308sawyer Silver $$ Contributor

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    If I would have told my Dad or Grandpa that I was going to put a cylinder sleeve for a tractor in an OVEN before trying to drop it into the engine block I would now have cauliflower ear!
     
  7. okie

    okie Gold $$ Contributor

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    put a lot of big bearings on shafts. shaft on dry ice. race/bearing in the oven...
     
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  8. fyrewall

    fyrewall

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    Stretching a rubber band (tension) is not a good comparison to heating a rifle barrel (thermal expansion). For the rubber band the engineering wizards would refer to the process as an example of Poisson's ratio (longer in one direction & thinner at a right angle).

    As for the mason jar, I seem to remember a lid surrounded with a stamped steel threaded ring that could be screwed in or out of a threaded glass jar clamping the lid shut against the glass jar. Heating the jar top usually grew the threaded ring making it easier to turn off. I would expect the circumference of the ring would increase and because of that I would apply any expansion coefficient to the circumference of the round object.

    Do people still buy mason jars?
     
  9. savagedasher

    savagedasher Gold $$ Contributor

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    I just put a 1/2 degree positives camber in the left axel tube and 1/2 negitive
    In the right using nothing but a tour he and cold water .
    Aluminum and steel has two different expansion rates .
     
  10. okie

    okie Gold $$ Contributor

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    yeah, put home made spirits in em here. wal-mart lol
     
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  11. okie

    okie Gold $$ Contributor

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    I like this kind of thinking. this is how change is made. improvements come from this...
     
  12. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    Yep heat straightening, you heat the side you want to shrink. And it shrinks, after it cools. My god! Just stop. There are no opinions here, just basics physics. Thermal expansion is past the theory phase. Steel expands with heat, you were wrong. Its ok. It happens. I'd delete this ridiculous thread but then we'd loose all this hilarious data.
     
  13. damoncali

    damoncali Gold $$ Contributor

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  14. okie

    okie Gold $$ Contributor

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  15. okie

    okie Gold $$ Contributor

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  16. Cloudrepair

    Cloudrepair Gold $$ Contributor

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    So would it make sense to have a steel picatiny base and aluminum six screw rings with the front one tight and the back one snug?
    To avoid loosening and tightening one maybe I should test that out tomorrow if I can get to the range.
    May not mean much in cold weather.
    I guess I will see if t repeats
     
    Last edited: Jan 12, 2018

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