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    Laminated Fiberglass Prod

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    Laminated Fiberglass Prod Empty Laminated Fiberglass Prod

    Post by RazorBack on Mon Sep 19, 2011 8:33 pm

    Hi all,
    I am new to the list and to making crossbows. I have been making laminated fiberglass longbows for a while now and I would like to try making a crossbow. I have been reading up on this and I am having a metal nut made by a machinist, but I want to make the prod myself. I just need to have a better idea how long to make it and how thick to make the woodstack. I use .040 fiberglass for all my bows so that is what I have. I am hoping for around a 100 lbs bow. I was thinking of about 36 inch prod so that it would not be too unwieldy. Any help will be greatly appreciated.
    Thanks,
    James
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    Laminated Fiberglass Prod Empty Re: Laminated Fiberglass Prod

    Post by Todd the archer on Tue Sep 20, 2011 3:12 am

    Welcome RazorBack, I have an Elk Ridge Archery prod. I'll try to give you it's measurements, but keep in mind I am measuring with a ruler not a micrometer.



    It is 118 pounds at 12 inch draw. 33 1/2" nock to nock. 1 3/8" wide at the center tapering to 3/4" at the tips. the riser from fade out to fade out is 8" and approx. 3/16" thick. the wood stack is about 7/32" thick and appears to to be all parallel laminations. I think the glass is .050" thick.



    One other detail is when looking at it from the front. The profile is a straight line on the top edge and the width tapering is done all on the bottom edge.



    Maybe this can give you a starting point. Let us know how you make out.



    Todd
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    Post by RazorBack on Tue Sep 20, 2011 4:37 am

    Hi Todd,
    Thanks for the help. This is exactly the kind of information I need. I have a few clarification questions for you.
    1. Can you see how many wood laminations they used?
    2. Is the wood stack 7/32 at the riser fades or at the center.
    3. The riser at 3/16 seems thin to me. Does the prod bend through its entire length or is the riser portion stiff? I was thinking of at least 1/2 thick riser.
    4. Do you have your prod tied on or is it bolted? I was planning on tying mine on with 1/8 braided nylon rope.

    Thanks again for the help. I really appreciate it.
    Best,
    James
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    Laminated Fiberglass Prod Empty Re: Laminated Fiberglass Prod

    Post by Ivo on Tue Sep 20, 2011 12:22 pm

    Hi RazorBack, Welcome to the forum.

    Unfortunately we don't have any laminated prod build-along topics yet. However, crossbow prod isn't *too* different from a vertical bow, so there is a great chance this will come naturally to you. Smile

    What I can offer to help is a few articles from Robin Allen's (God rest his soul) website - http://www.thecrossbowmansden.com/Home.html

    Robin Allen wrote:

    PRODD DATA
    Riser or wedge



    Veneer or laminations


    Para—Parallel


    Tapered Bingham’s tapered veneer


    D-W -- Draw Weight


    Two-limb prodd, left and right 18”or 16” limb mounted on a block, where-as the bolt is shot through the block.


    This data is for an 18” limb using a 2”x 7” riser with a flat profile, two limb prodd.


    Draw length of 14 ½ “.


    All Bo-Tuff and veneer to be 2” wide.


    All prodds were made using Rock Maple veneer.


    Riser woods Honduras Mahogany, Cocobolo, Rock Maple, and Laminated Rock Maple, Padauk.


    Epoxy Glue Airodite 2015 or Smooth-on, I
    now use Smooth-on, this epoxy will give you a much longer open window
    for glue up, it will cure overnight in a warm room


    BUT do not cure a prodd limb without a glue oven.
    All prodds were made using the same wedge (see drawing).


    The profile shape is the same in the prodds, (see drawing).


    NOTE: These are the prodd weights that I
    got from my prodd press shape, if you use the chart below, you may not
    get the same poundage, your prodd press may be a little different from
    the one that I use, and Rock Maple veneers are not always the same from
    one batch to another, I grind all my own veneers, I found that two
    veneers cut from the same board, ground to the same thickness, will not
    spine weight to the same spine number, this why I grind many veneers so
    that I can use all the same spine veneers on each limb.


    Using a different profile shape on the limb will give you a different draw weight.
    Draw Weight
    Materials
    #100
    1- 0.50 1- 0.30 bo-tuff, 1-para 0.75, 1- 0.75 tapered 1- 0.45 tapered
    #912- 0.40 bo-tuff, 1-para 0.70, 1-tapered 095.0
    #86
    1- 0.40 1- 0.30 bo-tuff, 1-para 0.75, 1- 0.25 tapered 1- 0.75 tapered,
    #86
    2- 0.40 bo-tuff, 2-para 0.70
    86lbs @ 16”draw length2- 0.40 bo-tuff, 1-para 0.80, 1- 0.50 para
    #78
    1- 0.50 1- 0.30 bo-tuff, 1- para 0.62, 1- tapered 0.65
    #70
    1- 0.30 1-0.40 bo-tuff, 1-para 0.90, 1- 0.65 para
    For heavy hunting prodds, you would use 0.65 bo-tuff and 0.95 or .100 veneer.


    I now use Bamboo veneer for my hunting prodds.


    How to increase the velocity of your prodd


    There a few ways, in which one can
    increase the speed of a prodd, some are easy and some are pushing the
    envelope of stress. Be aware of this before you start changing your
    prodd, remember once you have cut something off of your prodd you cannot
    put it back, you have to do right first time.

    Robin Allen wrote:

    PRODD LAMINATING PRESS


    What you will need to make this prodd laminating press.



    • Four pieces of ranger board 20”x 12”x ½”
    • One piece of 1/8” ranger board 20”x 8” x 1/8” or plywood
    • One strip of Formica 20”x 2”
    • One metal pressure strip 20”x 2”
    • One length of 2”x 24” fire hose
    • Two end plugs to fit inside fire hose
    • Four strips of flat mild steel bar 1”x10”x3/16”
    • Six 3 1/2”x1/2” bolts with nut and washer
    • Four 2” auto hose clips (hose clamps)


    This prodd press is for making one limb only. You
    will need two limbs for a set. The reason we make two limbs and not a
    one-piece limb, it is very difficult to shape a one-piece prodd mold and
    get it to be exact on both sides of the mold.


    Making this prodd press is fairly easy if you follow the basic rule
    that all sides of the prodd mold must be square, for this reason I use
    medium density fiber board (trade names Medite or Ranger board) for all
    my prodd presses. This is a man made product from sawdust and glue that
    is compressed under very high pressure, this board is dead flat on both
    faces, so all you have to make
    square, are the edges.

    First
    we glue up the four (4) pieces of 20”x12”x1/2’ Ranger board, you can use
    any good wood glue, scuff one side of the board with 120 grit paper, do
    the same with all the boards, two boards only one side, two boards both
    sides, this will give the gluemore surface to lock into, wipe all the
    boards to get rid of the sanding dust, or use a soft brush, you must get
    rid of the dust to get a good glue bond, apply glue to one surface of
    your board, scrub the glue into the board, (what this means is whatever
    you are using to apply the glue, I use a 2” piece of Bo tuff scrap,
    really work the glue into the surface of the board this again will give
    you a good glue bond) lay on a flat surface, then apply glue onto both
    sides of your next board, lay it down on the first board, repeat with
    the next board, on the last board only one side needs to be glued line
    up the parts as close as you can , you can screw the boards as well to
    give your press more strength, but make sure that there are no screws
    where you need to cut out your
    limb shape, check that all the pieces
    are lined up, load up the block with heavy weights, let this block cure
    for about 24 hours.

    You should now have a block 20”x12”x2”.

    You now need to square up the edges, do this on a tablesaw, or take it to someone with a tablesaw.

    Yes
    you could use plywood, I don’t use plywood because in Canada there is
    no ½” plywood, we have only metric, and as the Bo-Tuff that we are going
    to use is 2” wide the metric size plywood will not work out to
    thickness, anyway Medite seems to give me much smoother curves in the
    reflex part of the prodd and you end up with a much better prodd press,
    and some plywood will have parts of the lamination missing which you
    will have to fill in, the reason youdo not use lumber is after it has
    been planed to get it square it will not be 2” thick, your prodd press
    must be 2” thick, also a piece of 12”x 2” lumber that will be heated up
    to about 1208 to 1808 F would be
    prone to warping and twisting, and
    that, we do not want to happen, so use Medite or if in the U.S. you
    could use a good grade ½” plywood.

    Now we have the Medite block
    square, next thing we need to do is the shape of the prodd limb, for
    your first limb, stick to a simple recurve shape.

    This type of prodd limb has been proven over years of shooting.

    Find
    the center lines of the 1/8” Medite(plywood) that is the length line
    and the width line, this will make it easier to mark out the limb shape,
    transfer the limb shape onto the piece of 1/8” Medite, keep everything
    square, now cut out the shape of the limb, cut just shy of the line,
    then you can carefully file to the exact shape, now we go back to the 2”
    thick block, mark out the center lines as you did on the thin Medite,
    the prodd shape should lay along the center line, make sure that the
    edges line up, nail the profile prodd shape onto the 2” Medite block,
    just use ¾” brads for this, draw a pencil line about ¼” from the edge of
    the profile shape, cut on this line using a band-saw, cut out the prodd
    shape, an easy way to draw this line, use a small washer, lay it up
    against the profile shape put the pencil or what-ever you are using to
    mark out inside the washer and draw around the shape this will give you a
    nice even line around the shape. Now carefully saw around the shape
    just on the line, you now have two parts of your mold. Do not remove the
    1/8” Medite shape this is now used to sand the shape of your prodd on
    the sanding drum, (see how to make a sanding drum shaper) you must keep
    the Medite flat on the bed of the sander, check to make sure that the
    drum is square to the bed of your sander table or it will sand out of
    square to your prodd mold. (Photo). Check to see if it is square to the
    sides of the mold.

    Now that the mold has been sanded to shape,
    you can take off the 1/8” shape now, you will not need this any more,
    make sure that you have all the nails out, that is the hard part done, I
    now glue on a strip of Arborite to the part that we sanded this is to
    ensure that it is flat and it is easy now to apply wax when glueing up
    the prodd, you can glue this with epoxy or contact glue, file the edges
    square to the sides of the mold, now fit a plate at the riser end of the
    mold so that you can butt up all the parts of the prodd
    flush with the end.

    Now
    we have to fit both parts together, this is how I do this, the four 1”x
    3/16 flat bar is for clamping, drill 2 ½” holes in all four pieces in
    one end, I clamp two of the strips together and drill both at once so
    now you will have a drilled pair, this is to bolt to the prodd mold,
    make sure that the bolt holes line up with each other, in the other end
    of the clamping bar drill a single ½” hole.

    What you need to do
    now is have your prodd parts on hand, that is two pieces of 18” Bo-tuff,
    18” prodd laminations and your riser, lay down one Bo-tuff strip one or
    two
    laminations the riser lams Bo-tuff remember we are NOT glueing,
    lay on the metal pressure strip, this strip helps to give an even clamp
    along the length of the prodd, use parcel tape to hold all the parts in
    place, lay on the fire-hose do not inflate yet, now put on the top part
    of the mold, that is the part that you had left over when you cut out
    the profile of your prodd from the 2” block of Medite, line every thing
    up, clamp with a bar clamp each end of the prodd mold, not to tight,
    inflate the fire-hose with about 40lbs of air, now shine a light on the
    back side of the mold, and look to see if you can see light thought the
    prodd riser and lams, if you can increase the air pressure a little say
    5lbs check for light, if you can still see light, another 5lbs, but
    don’t go over 50lbs as you may have glue starvation, if you still have
    light showing, it will be the fade out on the riser, so make sure it is
    feathered out.

    So now we have no light showing thought the prodd
    parts, take the clamping strips that you drilled, and lay on the prodd
    mold, one each end, mark where the holes are, mark carefully, now let
    the air out of the fire-hose, take all of the parts off the prodd mold,
    drill ½” holes where you marked on the lower prodd mold, bolt the two
    clamping strips on to the mold, now drill top part of the mold, I do
    another dry run to make sure that every thing is in order, put the prodd
    parts back on the prodd mold with the metal pressure strip tape all the
    parts together put on the fire-hose, put on the top part of the mold
    and bolt up, check to make sure that every thing is o.k. This is the
    moment of truth, inflate to 45lbs of air, with the light at the back of
    the mold check for light, great no light showing, this means that you
    have a nice tight glue line, if you have light showing you WILL have a
    clue gap, this in turn will break the prodd.

    Now we can glue up
    the prodd limb, now apply masking tape to the smooth side of the
    Bo-tuff, this helps to keep the Bo-tuff clear of glue, and you can mark
    the centre of the limb a lot easier on the tape, I find the centre of
    each piece of Bo-tuff and draw a line down the length, when you are
    ready to cut the profile of the prodd you now have a centre line to work
    from, where you lay up the prodd on your bench must be free of dust and
    dirt, some prodd makers have a room just for gluing up so they can keep
    it dust free, I am not so lucky so we have to make do, lay down news
    paper on the bench, now put on rubber gloves or the very thin plastic
    ones, this is to keep the
    parts free of your skin oil, any oil will
    prevent a good glue bond, I now brush all the parts with a clean brush
    (I keep this brush just for this, stored in a plastic bag to try and
    keep it clean), this is to get rid of the sanding dust etc, now you
    should wipe all the parts with clean Acetone this will get rid of any
    oil and dirt.

    Lay all the parts out in the order that you are
    going to lay up your prodd, i.e. 65tho Bo-tuff, 45tho, lam 50tho lam,
    riser, 35tho lam, 65tho Bo-tuff, write this down so that you can be sure
    you have the right order when you glue up the other prodd limb.

    I
    use smooth on epoxy from Bingham as my prodd glue, this epoxy has a
    long open window, so there is no need to rush the gluing up this will
    give you ample time to get it right,

    IMPORTANT mix the two parts well for at least 5 minutes, use a
    clean plastic cup and stick I use coffee stir sticks, IMPORTANT when
    gluing up the prodd remember wet on wet, take your first Bo-tuff strip
    check that it is clean, start applying the epoxy on the rough side only,
    it is best to scrub the epoxy in to the part this will give you a
    better bond, lay this aside make sure you have covered all of this side
    with epoxy, hold up to a light and see if you can see any dark spots, if
    can go over it again, the dark spot has no glue, now do the same for
    the wood lams, now the wood lams have to have glue on both sides, This
    is how I do this I glue one side first, then I lay the glued side down
    on the Bo-tuff glued side (wet on wet) the I can apply the glue to the
    dry side of the lam, do the same for the other lam ( wet on wet ) now we
    can glue up the riser, Take care at the fade out it breaks very easy so
    apply the glue away from the feather edge, apply the glue to the other
    lam and bo-tuff, remember glue only one side of the Bo-tuff, wrap all
    the parts in kitchen cling wrap, place all the parts on the prodd mold,
    push all the parts hard up against the end plate so that all the parts
    are even at the riser end of the prodd, lay on the metal strip and the
    fire-hose put on the top part of the mold and bolt up, inflate to 45lbs
    check that you have no air leaks, with that all done put your prodd mold
    in to the oven to cure I cure my prodds for about four hours at 180 f ,
    I then let it cool down over night, do the same for the other limb now
    you should have a set of prodd limbs, but they have no shape in the
    profile this then is the next part, remember the line that you drew down
    the length of the B0-tuff, this is the line you work from, most prodd’s
    at the riser end would measure 1 ¾” wide, tapering down to 1” at the
    nock end, so at the nock end , measure ½” ether side of the center line,
    at the riser end measure 7/8” ether side of the center line , use a
    flexible tape for the next part, clamp the tape on your 7/8” mark at the
    riser end do the same at the nock end, the tape will follow the
    contours of the recurve prodd limb in a straight line, you can now draw a
    line down the limb, do the same for the other side of the limb, you
    should now have two lines on the limb.

    Draw the lines on the other limb.

    CUTTING OUT THE PRODD LIMB


    We Now have both prodd limbs marked out,
    cut on the waist side of the line do not try to get to close to the
    line leave yourself lots of room, as you will be grinding the rest off
    later, now you can cut the prodd with a hacksaw with a fine blade, use a
    new blade so that you can control the cut, saw slowly and carefully.

    To finish up the shaping of the prodd we
    go back to the sander, if you have a flat bed sander this will do a
    real good job of finishing the prodd limb to size, if you have to use
    the drum sander grind the limb carefully to the line, now we glue on the
    nock reinforcement, on the back of the prodd you need to glue two
    pieces of Bo-tuff about 1 ½” long at the nock end clamp and
    allow to cure overnight (use epoxy for this)


    MAKING THE FIRE-HOSE CLAMP

    You will need a length of 2”x 24” fire
    hose (Bingham or your local fire hall) two end plugs you can get these
    from Bingham or make your own, this is how you do it you need two
    plumbing on one of the parts solder a plate that’s all you have
    to do for this plug (see photo) on the other one solder a plate, but
    drill a hole for a tire valve now solder this valve into this hole, put
    the four hose clamp on the fire hose loose, apply epoxy glue in side the
    hose push in the end plugs make sure they are in as far as they will go
    now screw on the hose clamps tight, two on each end , let the glue set
    over night check to see you have no air leaks inflate to about 50lbs (
    fire hose will inflate to over 200lbs) I half fill the bath tub and
    check, if you have no leaks, that part is done.


    MAKING THE RISER OR WEDGE


    To make a good riser we need to grind it
    to a feather edge, this is so that we get a good glue line and every
    thing blends in smoothly at the riser fade out, (feather edge) (most
    prodds fail at the riser feather edge) to do this we have to make a
    simple fixture for grinding on the drill press sander that you have made
    for the prodd mold.

    The parts that you will need for this jig


    • A piece of Lexan or Pexi-glass
    • A piece of Medite
    • A block of wood
    • Screws
    • ½” ready rod with nuts and washers
    • Two lock down plates and butterfly nuts.


    This wedge (riser) has a very simple
    shape, the secret of a riser is to get the fade-out feathered very thin,
    so that you can see light thought it this jig will do this for you.

    THINGS TO REMEMBER WHEN MAKING A PRODD

    To
    make the riser you need a piece of high grade hard wood, Walnut, or
    Rosewood, must have no flaws or knots about 8”x2”x1” square this piece
    on all four edges, draw a line diagonal across the 1” face saw across
    this line you should have two riser shaped pieces.

    When cutting your Bo-tuff to the 18” length, cut it square across the piece.

    Use a hacksaw with a fine blade.

    Put masking tape on the Bo-tuff this makes marking out a lot easer, and helps to prevent tearing of the fibers.

    Wear gloves when handling Bo-Tuff.

    When mixing the Epoxy, mix for at lease 5 min, this is to ensure that you have ALL of the parts mixed.

    Scrub the epoxy into the parts, and make sure that all parts to be glued are covered.

    Clean all the parts with clean Acetone.

    When using any of the Rosewoods make
    sure that you have washed all the oil from the surface of the wood with
    Acetone, THIS IS VERY IMPORTANT!!! Oil in the Rosewood will prevent a
    good glue bond.

    When making the riser, make sure that the fade out is paper thin,

    Unfortunately Robin didn't include the pictures he referenced to in the article, so we're going strictly by numbers/experience.

    So, as you can see there are differences, but for most part the set up is the same as the one you would use for laminating limbs for a 3Piece TD - that is for a split limb prod.

    For a one piece it's more like gluing up a one piece vertical bow, with one exception - crossbow prods are symmetrical in their design. Also if no riser is used and the prod is retained in an angled prod socket, one will need to compensate for it - offsetting the limb tips to reduce string friction against the track as well as ease up the toque (limb geometry with tip rise that Todd is talking about).

    I bet quite a few things can be done differently as people who do them are different and have some of their own tricks up their sleeve, but these are the guidelines I have on hand. Good luck! Smile

    Hi Todd,

    To help the topic Smile...Can you please post a few pictures of your bow with the laminated prod, shot from different angles? Not much, just side, top, and front. Thanks you in advance. jocolor


    Ivo



    Laminated Fiberglass Prod Untitled
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    Laminated Fiberglass Prod Empty Re: Laminated Fiberglass Prod

    Post by RazorBack on Tue Sep 20, 2011 8:17 pm

    Thank you Ivo,
    This was very useful. His description of the riser sounded like he was putting a separate 8" riser on each limb. If that is true, than he would have a 16" riser on a 36" prod, unless I am missing something. That would make the limbs very stiff as it would create very short working limbs and it seems like it would set you up for failure at the riser fades. Todd said his riser was 8" on a 33 1/2" prod with a wood stack at the fades of about .220 (I divided 7x 32)

    Robin's layup for a 100# prod is
    1- 0.50 1- 0.30 bo-tuff, 1-para 0.75, 1- 0.75 tapered 1- 0.45 tapered Total wood stack of .195 Total Stack of .275
    (I think he meant .075 as that is how the micrometer reads.)

    Since I am using .040 glass for both belly and back my layup would be very similar. But I will not be recurving the tips. My glass is only 1.5 and I will be laying the prod up as one piece.

    To compensate for limbs narrow than Robin's and longer than Todd's, I am thinking that my layup formula might be something like this:
    .040 glass
    .090 Parallel
    .060 Tapered
    .090 Parallel
    .040 glass
    total wood stack .240
    total stack .320
    riser 8"x1.5"x1" with 2" fades
    Estimated Draw weight: 100# @ 14"

    I think that should get me into the ball park and I can adjust the width and length of the limbs to bring the weight up or down.
    I would be interested in any input on this reasoning and on the layup formula.
    Thanks,
    James
    Todd the archer
    Todd the archer
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    Laminated Fiberglass Prod Empty Re: Laminated Fiberglass Prod

    Post by Todd the archer on Tue Sep 20, 2011 9:49 pm

    Here is a pic of the prod. Will take other pics tomorrow. The riser is 8" fadeout to fadeout. The wood stack at the fadeout is about 7/32". The center of the riser is about 3/16" thick PLUS the wood stack of 7/32". I guess you would call the riser semi-rigid. Hard to count the number of lams, looks like 5. My prod is tied in. It is now tied in with 1/8" braided nylon cord. This pic shows it with leather lacing which has been changed since this pic.



    Laminated Fiberglass Prod DSCF1425



    Todd

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