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    Leaf Spring Troubles

    Pellethuntr
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    Post by Pellethuntr on Wed Feb 23, 2011 8:20 pm

    Hi guys sorry for any newb questions I did a search but could not find the info I needed.. I am having a lot of trouble with making prods.. I bought a trailer leaf spring today this one to be exact http://www.tractorsupply.com/trailers-towing/trailer-parts/other-trailer-parts/trailer-springs/carry-on-trailer-eye-to-eye-leaf-spring-1000-lbs-capacity-1750195 .. I took it apart and found that it was still extremely stiff and it didn't want to bend much for me try as I would.. So my question is what am I missing? Does it need to be cut? If so how do you suggest? I was thinking that if I cut it in half length-wise I would then have two sets of prods about 1 inch wide.. but then it might be to week.. So any help you can give me is much appreciated Very Happy
    mac
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    Leaf Spring Troubles Empty Re: Leaf Spring Troubles

    Post by mac on Wed Feb 23, 2011 9:02 pm

    Pellethuntr,

    First of all, that thing is designed to work as a stack of leaves. If you take it apart, it will bend too much in the center.



    I would....
    -- cut the rolled mounting lugs off;
    --cut the height of the spring down to about 1/2 or less at the tips, leaving a bit of extra material for the shoulders of the nocks. Cut from the bottom of the spring, so that the nocks will be above the center of the bow.

    An idealized profile for a spring (a bow is just a "spring with a string") with a constant thickness would taper from its maximum height in the center to points at the ends of the limbs. This is obviously not possible for two reasons. First is that the nocks must have some height. Second, your spring has a big mucking hole in the middle. Therefore you will have to deviate from the ideal by leaving extra material for the nocks, and extra material around the center hole. If you don't leave more material around the center hole bow/spring will flex more in the center than elsewhere. This could well lead to premature failure in the middle.

    By the time you have thinned the limbs, the bow/spring will be significantly "lighter" and more flexible.

    Does this make sense? If not, I can try to post a diagram tomorrow.

    Mac
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    Post by Pellethuntr on Thu Feb 24, 2011 7:54 am

    A diagram would be great thanks for the reply Mac .. As far as the flex being in the middle, I was planning on cutting the spring in half where the hole is located and mounting the limbs separately.. I had another thought.. I was looking on Ebay at crossbow prods and I see that there are quite a few for sale in the 100-150 lb range.. If I return the leaf spring I will have about $30 back what do you guys think of these for a first hunting crossbow??

    http://cgi.ebay.com/CROSSBOW-150-LBS-Prod-FIBER-GLASS-Replacement-LIMB-Sets_W0QQitemZ250777702538QQcategoryZ36100QQcmdZViewItemQQ_trksidZp5197.m263QQ_trkparmsZalgo%3DSIC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D10%26pmod%3D250761573454%26po%3DLVI%26ps%3D63%26clkid%3D7314523630487961682

    http://cgi.ebay.com/CROSSBOW-130-LBS-Fold-Up-MK-180-Prod-Replacement-LIMB_W0QQitemZ250777521539QQcategoryZ36100QQcmdZViewItemQQ_trksidZp5197.m263QQ_trkparmsZalgo%3DSIC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D10%26pmod%3D250761573454%26po%3DLVI%26ps%3D63%26clkid%3D7314549873302091372
    mac
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    Post by mac on Thu Feb 24, 2011 8:36 am

    Pellethuntr,

    The one piece fiberglass bow should work well. I've used the ones that Barnett sells.

    I'm a medieval guy, so I would never think of using individual limbs. Perhaps someone else her can advise you about them.

    Mac
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    Post by mac on Thu Feb 24, 2011 8:53 am

    I made a quick sketch of how I would cut that leaf spring, but I can't figure out how to attach it to a post.

    Can someone help me here?

    Mac
    Pellethuntr
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    Post by Pellethuntr on Thu Feb 24, 2011 10:05 am

    Thank you for the help again Mac.. I think I will be buying one of these prods soon.. The reason I like the two piece prod set is becuz the design I have in my head allows the prod to be perfectly in line with the track, basically the arrow will pass through the "center" of the prods.. like the one pictured.. I like the two piece prod set for that reason and becuz id like to be able to just un-string the bow and un-bolt the prods for easy take down and transport..

    Leaf Spring Troubles 2008712157Leaf Spring Troubles Moz-screenshot-1
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    Post by Basilisk120 on Thu Feb 24, 2011 11:25 am

    Here is a link to explain how to post pictures: http://thearbalistguild.forumotion.com/t2-posting-pictures-video-tutorial

    Thats porbably a better explination than anything I can come up with quick.



    Something Something Dark Side
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    Post by mac on Thu Feb 24, 2011 11:45 am

    When I try to follow those directions I get an error message at the point where I press the "host it" button.

    Unable to create directories : /home/servimg/u/f72/16/22/66/39/

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    Post by Basilisk120 on Thu Feb 24, 2011 2:20 pm

    Hmm I haven't tried the "host it" feature. All my pictures have been located on photobucket. I wonder if you have to have a logon to Servimg.com to use that feature? I'll try to look into it when I get home.



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    Post by Pellethuntr on Thu Feb 24, 2011 3:50 pm

    Ok I have decided on buying my prods.. So no worries about your pic Mac.. Any one have any suggestions on which to buy?? either way I will be using a "split" limb design.. So I would like to use the 150lb prod for the extra fps, but im unsure if it would be ok to cut it in half?? Or I could just go with the 130lb any advice is welcome and appreciated
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    Post by Pellethuntr on Sun Feb 27, 2011 12:35 pm

    Bump.. could still use some help if any one has any suggestions Smile
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    Post by mac on Sun Feb 27, 2011 1:10 pm

    I would go with a more conventional sort of bow. If you go with two separate limbs you will vastly complicate the construction; all for a *possible* few more feet per second.

    This is your first crossbow, yes...? Separate limb construction also significantly increases your chances of structural failure. Make your first foray into crossbow construction simple. You can do something higher tech on some later bow.

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    Post by Ivo on Sun Feb 27, 2011 7:09 pm

    Hi Pellethunter,

    Mac has a point there.

    Risers are kinda on the advanced crossbow building end, however it's not impossible.

    The pro's and cons of riser/no riser:


    Riser (Split Limb / Full Limb)
    No riser (Full Limb)
    Weight

    Crossbow is Front Heavy

    Light front end
    Compactness

    Wider prod(limb) for the same draw length.
    Limb(s) need to be longer to account for mounting seats.
    Shorter prod can be used to get the same draw length as the mounting space is minimized allowing a better part of the limb to work(bend)
    Limb system suitability

    Risers can be designed with different limb angles(from parralel to past parralel) and can even be designed for an adjustable limb angle and thus can be used both with the bare limbs(D-bow or recurve) or compound assemblies(cammed limbs).


    Mainly used with bare limbs.
    However crossbows with a compound limb mounted under an angle have been spotted on the outskirts of Russia
    Smile
    String Friction

    Less to none. String travels straight whether track is present or not. Take care when cutting string nocks as that is one of the elements that is responsible for string height

    More. Varies with prod mounting angle and string thickness. More about mounting angle troubles here...link
    Ease of construction
    Moderate to Advanced - Special tooling and materials may be required depending on the design.

    Easy to Moderate - prod can be mounted straight to stock/rail. Cutting a seat with proper mounting angle and stock reinforcement issues seem to be the only major points...the rest lies with the bow "design" and mounting options.

    Mounting

    Special care should be taken when mounting
    risers as great amount of torque is produced.
    May require a mounting block bolted to the stock or incorporated into the front end of an arrow track.


    Force is directed along the stock axis.
    Can be cord bound or mounted using bow irons.
    May require a reinforcement bolt to keep the stock from splitting with heavier weight bows.
    If I missed something or am mistaken, please correct me... Smile

    A riser can also be used with a single limb.

    One example where limbs are below the track level is Taiwanese crossbows that press the limb in the center with one bolt using a small steel plate as a spacer(not to harm the limb).
    Leaf Spring Troubles Cb510

    And another version that is with a shoot through single limb...more about it here Crossbow Books - Match Target Crossbow Article
    Leaf Spring Troubles Shoot_10

    The most basic riser I can think of is a piece of angle iron as in the picture...only iron mounted backwards and/or with limbs mounted on the outside to keep the pressure on the riser rather than just the mounting bolts (Pavise explained it here>>>link)
    Leaf Spring Troubles 3up1010


    About leaf springs...there is an old article that might help you a bit with the tillering(adjusting limb proper bend)

    http://www.vintageprojects.com/archery/crossbow-leaf-spring.pdf

    ...as well as a great crossbow building resource by basileus that also speaks of using leaf springs.

    http://thearbalistguild.forumotion.com/t276-good-page-on-construction?highlight=great+page

    [Edit]

    Pellethuntr wrote:...I had another thought.. I was looking on Ebay at
    crossbow prods and I see that there are quite a few for sale in the
    100-150 lb range.. If I return the leaf spring I will have about $30
    back what do you guys think of these for a first hunting crossbow??

    http://cgi.ebay.com/CROSSBOW-150-LBS-Prod-FIBER-GLASS-Replacement-LIMB-Sets_W0QQitemZ250777702538QQcategoryZ36100QQcmdZViewItemQQ_trksidZp5197.m263QQ_trkparmsZalgo%3DSIC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D10%26pmod%3D250761573454%26po%3DLVI%26ps%3D63%26clkid%3D7314523630487961682

    http://cgi.ebay.com/CROSSBOW-130-LBS-Fold-Up-MK-180-Prod-Replacement-LIMB_W0QQitemZ250777521539QQcategoryZ36100QQcmdZViewItemQQ_trksidZp5197.m263QQ_trkparmsZalgo%3DSIC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D10%26pmod%3D250761573454%26po%3DLVI%26ps%3D63%26clkid%3D7314549873302091372

    That #130 limb set isn't powerful enough...it's good for target shooting with light small diameter aluminum shafts, but anything heavier bounces off the target...just my personal experience.

    As for the #150 prod...I've been on and off building my younger brother a crossbow for hunting small stuff...don't have any up to date pictures since I started making videos, but there is an older photo with a piece of angle iron and wooden wedges as mounting(couldn't wait to test the trigger Razz )
    Leaf Spring Troubles IMG_4013
    Leaf Spring Troubles IMG_4002

    ...at around 14" draw (probably the limit with that prod) that things packs a punch...who would have thought some #20 would make such a big difference. Smile

    [Edit]



    Leaf Spring Troubles Untitled
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