Band life - a new approach

Discussion in 'General Slingshot Discussions' started by JoergS, Sep 19, 2013.

  1. JoergS

    JoergS Administrator

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    I have been doing a lot of shooting these last few days, as I don't have to go to work anymore (hopefully for EVER!). I love YouTube!

    Anyway. So far, I pretty much thought that tapering and band stretch are the only factors that have an impact on the band lifetime. No tapering, low stretch = many many shots, extreme tapering and stretch = very very few shots.

    However that isn't the entire story.

    My new through-the-insides shooter easily doubles the lifetime of a band vs. OTT frames. That's right. I got more than 150 shots from a 3:2 tapered band that I stretched to factor 6 (= as far as possible). That band would have lasted maybe 50 shots, 70 shots tops, on an OTT frame.

    Then I cut a totally untapered bandset for an OTT shooter, same stretch. It broke after about 80 shots. However the important part is: It breaks at the pouch, just like the tapered bands do.

    I now believe that one of the main reasons for the bands breaking at the pouch isn't the higher stretch. Maybe it is the impact of the bands when they snap back. The ITTF slingshot leads to way less violent hits because the don't have that hurling effect, but go straight back through the fork.

    In other words: The OTT method leads to hits of the bands to the hard parts of the frame.

    I now cut a loong bandset (40 cm active length), entirely untapered, 3cmx3cm, 2 bands per side. I attached it to the hand braced slingshot I made some time ago, but I "upholstered" the front with some thick leather.

    [​IMG]

    Let's see how long these bands last!
     
  2. kineticweaponry

    kineticweaponry Senior Member

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    Cool idea! I thought it was sandpaper on the front, that could also be a cool experiment.
     

  3. KnuckieG

    KnuckieG New Member

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    That's just brilliant Jorge but what about factors such as storage,age,humidity,temperature,and exposure to sun light. Do you have advice regarding those things? If you solve those problems you might be able to give up your youtube job lol! :D

    Out of interest I wonder what the bandlife is like in Tobias' cow hide covered slingshot?
     
  4. KnuckieG

    KnuckieG New Member

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    Off the top of my head perhaps it isn't just the impact of the bands and pouch on the wooden frame but also the friction? A wad of padding covered in teflon cloth would absorb the impact but "teflon cloth" PTFE

    http://www.fennerprecision.com/capabilities/fabrics/low-friction-fabrics.php

    http://www.ebay.co.uk/itm/Non-Stick...Crafts_Sewing_Supplies_MJ&hash=item257f5eb125

    would be super slippery to avoid friction making the impact localise and increase damage? Just a musing.

    Like if Wile E Coyote fell off a motorbike at speed on a road surface he'd be grated like cheese but if he fell off onto a teflon road he'd slide right off undamaged... before falling off the cliff :D
     
    Last edited: Sep 19, 2013
  5. BeMahoney

    BeMahoney Builder of things

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    pardon me,

    hi Jörg,

    I don´t get it..
    Are you refering to that "TTF Rambone experiment" or to the Slingshot shown in this thread?

    If you refer to the "TTF Rambone experiment", then I get your point.
    There is that simple archaic principle of a fork, rubber and a pouch..
    And as always perfection means to master the joints, the attachments.
    Yet I think that there is some more efficient "truth" to be found thinking
    about the pouch (mainly about weight, softness and the vectors of inner forces)...

    Greetings,

    Be
     
  6. CEZ

    CEZ New Member

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    Cool, can't wait for the results, band breakage is a big issue for me.
     
  7. AngelicScars

    AngelicScars MILF of the board

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    Interesting!
    I think what was brought up is good to factor in as well (weather, how it's stored and whatnot).
     
  8. Jeremy

    Jeremy Senior member who totally rocks a pink Scout! Pink

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    I agree. I'm sure there are other factors to be considered, besides the bands slapping back into the forks with an OTT shooter. I do believe that J?rg is onto something though.
     
  9. JoergS

    JoergS Administrator

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    The idea for now is to find out if a longer band without any tapering and a "cushioned" OTT frame will lead to long band life.

    Then I will do the same setup with ITTF frame.

    The hunt for the longest living bands!

    BTW I clocked the setup... 53 m/s with the 33g 20mm steel ball... 46 Joules. Not bad for no tapering and stretch factor 4. Draw weight is pretty acceptable at that low stretch.
     
  10. Lacumo

    Lacumo Member

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    I'm interested in seeing what this study develops. I'm presently saving up HDPE and I'll probably start making frames in a few weeks. I'm still undecided on the OTT vs. TTF quandary.
     
  11. dolomite

    dolomite Banned

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    i've found that not using golf ball sized steel will allow my tbb to last at least 200 shots;). the projectile weight has a lot to do with band life. but big impact is so fun. then again, with nerve damage in my pouch hand, heavy bands and large shot just isn't feasible. with 4x3 tapered tbg i nearly had a negligent discharge, damn that cyst!
     
  12. JoergS

    JoergS Administrator

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    I shot and shot and shot that bandset today until I was very exhausted... probably 300 shots on it and no sign of tearings.

    I measured my draw on that slingshot, came out at 157 cm (full butterfly) pure band length (pouch not counted). The draw weight at that stretch came out at 11,5 kg (new Thera Band). Stretch factor is 3,97.

    Then I made a band setup for the same frame, using 25% more narrow rubber (4,5cm per side instead of 2x3cm=6cm). But I cut it to an active band length of 28,5 instead of 39,5cm. The final stretch of that band set is 5,5. Draw weight was a bit higher at that stretch, about 12,5 kg.

    The result: Both band sets shoot just the same. If there is any difference, then the shorter band set is a bit weaker. Even though it has a higher draw weight AND a longer acceleration.

    Maybe I was all wrong. I thought the stretch must be extreme for good performance. Seems like that is not the case, at least not in full butterfly with a slight draw increase (10 cm).
     
  13. Cadman

    Cadman New Member

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    Would this be a better test? Make a xbow with a sliding fork and a trigger. One sliding fork should be OTT and one TTF, ore you could make one designed for both methods. Shoot a series of shots at each stretch length that you want to test. This would be easier on your arm and shoulder, and allow you shoot all day long. Just my two cents worth.
     
  14. JoergS

    JoergS Administrator

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    Well, loading a crossbow takes a lot longer than loading a slingshot... I can shoot 100 balls with a slingshot in maybe 20 minutes. Would easily take me an hour with a crossbow.
     
  15. Arturo Borquez

    Arturo Borquez Administrator

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    Very interesting topic Jeorg, I agree that impacts plays a big role in band life. I also found out that the part of the bands that usually hits in recoil is near the pouch/ties, another source is band abrasion (lower face). Currently I am using "turn and tweak" PFS technique (for all frames) and noticed that the (tapered) bands lasts a way more even stretching to maximum, it seems that the bands and pouch assembly flies clean over the fork, and adding a flip (to avoid the slap recoil), so a cushion device or a way to avoid the slaps is a plus ...
    Cheers
    Arturo
     
  16. CEZ

    CEZ New Member

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    That is some interesting data! Do you think it would work the same for smaller ammo at higher velocity?

    Also how long did the 5.5 stretched bandset hold up? Doesn't stretch factor shorten band life?
     
  17. JoergS

    JoergS Administrator

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    Both bandsets are still intact. I put another 150 rounds on the long bandset, so that one is now close to 500 shots.

    I have probably done 800 12kg-45Joule-shots today... I can really feel it in my arms, hands and fingers. Landed 36,000 Joules of energy into my catchbox... 26kg steel, 9,6 tons of draw weight. Enough for one day.

    I don't think that you can reach top speed without tapering, but once I am through with testing the straight, long bandset, I will try tapering in combination with the lower stretch and cushioned slingshot.

    Maybe we will all go that way soon... cutting the bands 25% longer, but also 25% wider. Same draw weight, same power, longer bandlife. Hopefully.
     
  18. Cadman

    Cadman New Member

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    I was thinking of a more consistant testing proceedure and using the xbow as a fixed test apparatus. However, you are far more experienced than I, and I bow to your expertise. :)
     
  19. CEZ

    CEZ New Member

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    Quite the work out, maybe you should intentionally somehow shorten the bandlife a bit just so you don't have to put out so many shots to find out how much a bandset can take?
    I am still amazed by the less stretched bandset result, I'm definitely going to try that out myself.
     
  20. JoergS

    JoergS Administrator

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    Ok, after just a few shots this morning, bands broke. Guess where? Correct, right at the pouch side as always. No tapering.

    Cut the same amount of rubber, same band length again, but this time with a 2:1 tapering.

    Was 3cm x 3cm x 42cm
    Now 4cm x 2cm x 42cm

    2,5cm of course are needed for the attachments, active bandlength is 39,5cm for a net draw of 157cm. Just under stretch factor 4.

    The tapered band set does about 7 to 10% better in terms of speed. 53 Joules instead of 46. Weather is a bit cooler today, about 12 centigrade vs. 14 yesterday.

    Put the first 80 rounds through the new set, so far no tearing.