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Thread: crossbow limbs/materials

  1. #1
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    crossbow limbs/materials

    How much is openly known about current crossbow limb materials/suppliers and how the limbs are actually made? Do different major manufacturers use different materials? Is Gordon a main supplier?



  2. #2
    I know that gordon supplies the glass in a very raw form to Horton. Then they make their own limbs with it along with limbs for some other well known verticle bow line companies.

  3. #3
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    So the crossbow manufacturer

    takes the raw glass and shapes/forms the limbs? Is that a patented process?

  4. #4
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    Excal makes their own. I've seen the process....and it's a secret!
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  5. #5
    Quote Originally Posted by Moonkryket View Post
    takes the raw glass and shapes/forms the limbs? Is that a patented process?
    I don't know for sure. I would think it would be.

  6. #6
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    Gordon and other manufacturers supply a few companies with finished limbs. Not all of them have the manufacturing ability to make their own limbs
    Wyvern

  7. #7
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    I visited Gordon's site last night

    Interesting stuff!

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    The best xbow limbs in the world are made by Dave Barnesdale for Allan Kauthold. These are the target limbs used by most TNC Members. Stan Pennypacker also makes limbs-I don't know where he gets his blanks. The Excalibur limbs are very good for factory limbs
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  9. #9
    The best material for construction of bow limbs is one that stores a lot of energy in a small displacement and weighs little.

    The best possible material is ceramic. This however only in theory since it is based on a crystalline structure free from defects which today is unattainable.
    The best practical material is carbon fiber composites.
    The most common material is glass fiber composites because it is cheaper.

    Both composites require the same basic manufacturing process. A core of light, flexible and incompressible material which typically is wood and in the best cases is nomex honeycomb. On either side of the core resin is applied. Then one or more layers of fiber (tape of unidirectional fiber) and then resin again. Everything is enclosed in a stamp which has the function of keeping all firmly in place. The stamp is separated from the resin by a film of plastic material which will keep it from bonding to the resin.
    Then everything is placed in a special pressure oven and cooked for the specified temperature time profile and at a specific pressure. The exact specifications vary with the fibers and the resins used.

    It is worth noting that even combinations of carbon fiber and glass fiber can be used on the same limb. (and this is actually already being done) In this case the carbon fiber having a higher stress to strain ratio will go on the inside and the glass fiber on the outside. The two materials will be further separated by an appropriate thickness of core material. Of course both sides of the limb are identical. That is they are symmetrical around the central core. This is done for simplicity and is entirely reasonable since the fibers used have the same stress to strain response both working in compression as in elongation.

    Speaking of fibers it must be kept in mind that there isn't just one type of glass fiber or of carbon fiber but there are dozens with greatly varying physical characteristics and prices.

    All the manufacturing processes are not that difficult to replicate from scratch. The equipment could cost in the hundreds of thousands. The reason whether to manufacture your own limbs is purely an economical one. There aren't really big secrets, but there is a certain know-how involved and a learning period.

  10. #10
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    It seems that crossbow limbs

    are solid materials with no laminations. Is that correct?

  11. #11
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    To keep things short.

    Gordon makes pultruded limb blanks that can be machined to make a specific limb profile. These appear to be homogeneous in construction with no laminations apparent. They also make sheets of pultruded glass with various grain directions and thicknesses. There are multiple grades of glass and resins to choose from and of course graphite fibers (which are a waste on archery limbs because they are essentially too stiff).

    These pultruded and ground blanks can then be laminated with various stiffness (material property) and fiber directionality (orientation). This is typical with a Premium Limb builder such as Barnsdale. You may also choose various core materials with which to laminate.

    You can also make a compression thermoset limb which puts resin impregnated fibers into a thermoform mold which uses heat and pressure to permanently mold a limb to a specific shape. The limb is then seasoned and machined to its final shape. This is typical of a Bear limb and requires expensive molds and presses. I have seen prepreg laminated sheets inserted into thermoset limbs prior to pressing for cosmetic effect.

    Basically there are a few methods: pultruded (homogeneous), hand lay up from pultruded blanks or compression set limbs.

  12. #12
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    So a recurve crossbow limb is

    thermoformed where the material is poured into a mold and shaped?

  13. #13
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    Thermoset limbs are manufactured by wrapping glass yarn (which has been saturated with resin) around a mandrel. The mandrel simply holds the strands in a uniform way and then the resin saturated yarn is put into a mold. Think of the mandrel as your hands held at shoulder width while someone wraps yarn from one hand to the other in a clockwise fashion. The mandrel itself does not go in the mold.

    Using heat and pressure the resin is cured in the mold until hardened (set).

    During this process the excess resin oozes out of the mold (making a nasty mess). It is critical to the glass to resin ratio that the mold to be set to a very specific thickness. Limbs of increased stiffness need to have additional strands of glass yarn applied so the mold needs to be adjusted so that the glass to resin mixture remains constant.

    The cured limb is now cut off the uncured wet yarn at both end. The limb is then machined to its finished dimensions.

    The idea is to get the limb as close as possible to its finished size and shape with the mold. Final machining such as the axle hole or pivots must be done after it leaves the mold.

  14. #14
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    Crossbow limbs

    As some one said, more stored energy in a small displacement with less mass/weight. .I think maybe in the future some one will come up with such a limb material.

    This will be a major break through for the crossbow industry as well as the consumer.


    And I want one.
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  15. #15
    Based on what SE wrote it looks like most crossbow manufacturers take the shortcut of having the limbs made of purely yarn and resin.

    The more sophisticated process I outlined is used in some bows.

    It is a shame that even under todays good market conditions so little effort goes in making better and more efficient limbs in crossbows. The reason can probably be traced to the scarce technical education of the consumer and the stronger attraction to more superficial characteristics which provide little incentive for the manufacturers.

    It might also be a matter of inertia and closed and lazy thinking. The adoption of advanced CF leaf springs should cut by at least 70% the weight for the same rigidity of cheap GF construction. That would greatly improve speed and reduce launch stresses and noise.

  16. #16
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    So, in your opinion for crossbow limbs from Excalibur, Bowtech ad Ten Point (for example), which I thought were pretty good limbs (for crossbows), do you think their limbs could be cost effectively improved, and if so, how? I personally don't think increased speed is even needed in today's crossbows so is the difference a practical measurable difference in areas like vibration reduction, noise reduction and weight savings?
    Last edited by Moon; August 29th, 2008 at 07:39 PM.

  17. #17
    I don't know what each manufacturers limbs are made of.

    By my estimation a top quality cf limb should have 70% lower mass compared to gf only brick. How would this affect performance it's difficult to estimate. It's certainly not going to make it silent. It is going to improve efficiency and this means either less work in cocking it for same output energy or more arrow speed for same work. Possibly efficiency for a typical arrow weight could go from 85% to 88%-90% ? speed from 300 to 315 ?

    'cost effectiveness' depends. Its certainly more expensive but speed sells and even the idea of advanced limb, carbon fiber ... should have a certain appeal for some. It's about proving one's product technical superiority and that could be a selling point. Or so I would think but clearly the crossbow industry disagrees.
    My point is that people will pay for camo, and the manufacturers will even pay royalties for the most fashionable patterns when for the same money they could make a better limb and a better crossbow. And if one wants the stealth effect one can always tie some leaves and vegetation on the crossbow.

  18. #18
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    Good post :-)

    I agree that camo patterns are given way to much importance but manufacturers must try to give the buyer what he wants and thinks he needs

    I thought the current limb technology from Bowtech, Ten Point, Excalibur and Horton is very good. They are all dependable, with speeds in the 325 to 400 fps range and I, for one, believe that these speeds are more than adequate for hunting any game animal on this continent and I personally have no interest in a crossbow that shoots much over 400 fps for several reasons but I would be interested in crossbows that shoot 350 to 400 fps using less draw weight to achieve it. Minimizing maintenance levels, mainly string and cable servings, is important and would likely be a benefit of more efficient limb tehcnology that would equal the speeds of heavier draw weight and less efficient limbs.

    Let's see what the crossbow manfuacturers have coming in new technology at the trade shows in January

  19. #19
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    ras wrote -

    'cost effectivness' depends.

    While I don't have any experience in any...type of bow limb.

    I do have some knowledge in carbon fiber drive shafts for "Pro Stock" drag race cars.
    With the same "better"...thought in mind...many, many years and only moderate success was made in building strong..light weight drive shafts that would stnd up to the task of transfering the engine power to the rear wheels.
    Even with all the money, the different ideas of the top minds that know how all the different carbon fibers, the resins and the different methods of layup work....and the years of R&D....most all Pro Stock teams are back to aluminum drive shafts.

    I do understand this is a very different application...with current knowledge and materials...the desired outcome has not been reliably found.

    All this is to say....it MAY NOT...just be beacuse of money, or knowledge, (technical expertice), or the desire to make a better /different product.

    It MAY just be...with current materials and knowledge...it's not a viable option in todays world.

    Look out for tomorrow though!

    Mike

    P.s. - yea...camo patterns...now that's a subject for a rainy day, to get peoples blood pressure going straight up...!
    Last edited by Mike-; September 3rd, 2008 at 11:21 PM.

  20. #20
    It's not about technical impediments. I have visited a bow production facility where bow limbs were made with cf or the cf gf overlay technique I described. I also got from him a few meters of cf and gf tapes and resins for my experiments.
    I'll post the guy's name when I retrieve / remember it.
    Based on that I assumed most all limbs where manufactured that way. I was wrong. But it's only for commercial reasons that they are not.

    Sometimes the manufacturers simply don't see an opportunity because they have their tested way of doing it, because the consumer is not technically savvy or curious or educated, because they are distracted thinking of new designs or new marketing gimmicks.

    cf construction has a long history and the techniques have evolved. cf composites nowdays are sufficiently well understood and their techniques mature for them to be used in boats and in aerospace. In high performance sailing boats cf has replaced aluminum in masts and it's also used for hulls. The aerospace sector is interesting for another reason; many consumer sporting products now employ so called "aerospace alloys" meaning some aluminum alloy. Well, those alloys were introduced by the soviets in aircraft construction in the seventies! Now aerospace uses cf and new alloys such as magnesium based.... but to listen to the marketing people you'd think aluminum was the coolest thing around. The sporting products industry lags behind and the crossbow industry must be the slowest laziest sub sector around. If this was acceptable and natural when the market was small and stagnant it's no longer in view of the many years of above average growth it has enjoyed. The manufacturers are accumulating profits and are not investing it in technical improvements and even their competing is mostly based on non technical factors. The only exception being BowTech which stirred up things a little.

    In any case the technical challenges in using cf in archery limbs are tiny compared to those in aerospace or boats or motor racing. Just think of the differences in forces directions, tolerances, operating conditions.

  21. #21
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    So when a person chooses a

    Desert Stryker from Bowtech, he's getting the most advanced limb technology available for crossbows or are you referring to the original Stryker with its unique limb coverings?

  22. #22
    I don't think BT's limbs materials are any different from other xbow makers and they certainly arent carbon fiber otherwise you bet they would have heard about it just look at how they managed to put the word "carbon" even on a black painted ds! I'm just saying that they tried something technically innovative for crossbows with their pulleys and with the limbs retaining structure on the ds. (but both came from their bow products and both products have had reliability issues)
    Speaking of innovation I neglected to mention the reverse draw especially in the leopro by arncross and the HDT implementations of the concept. Both with all the question marks tied to their likely limited market impact and apparently some legal issues of which i have read about on this forum.

    And the aluminum thing was reference to those who claim to be innovative by using it... even for the limbs .... and maybe with holes drilled in them .... LOL

    More money going around but very little innovation.

  23. #23
    There is also the Twinbow. It seems like a good idea but unfortunately it is a flawed concept. The limbs will tend to twist, there's excessive wear on the servings, it won't take standard arrows and their vanes need to be cut and basically it doesn't deliver any significant advantages existing models.

  24. #24
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    I personally think the BT

    limb reliability thing was blown way out of proportion as I know for a fact at least one other manufacturer had limb problems where they did a masterful job of hiding it or kept it from being blown out of proportion with exceptional customer service. The limb problems seemed to normally happen with so called high perfomance crossbows in the 340 to 400 fps range. Those same bows seem to be very reliable now. At least mine are and with a high performance crossbow like the Desert Stryker or Phantom, I wold tolerate some limited additional maintenance.

  25. #25
    Our views differ on this. I think BT didn't nearly get as much open criticism as was to be expected for their limbs problems on the stryker. As for 10pt I hadn't even heard about that! Good to know.


    In any case to me the reliability issues of high performance crossbows just highlight a need for innovation. If you replace gf brick with cf laminated the residual energies and the stresses as the limbs come to a halt will diminish.

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