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    loose laminate issues

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    Anatine Duo
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    loose laminate issues

    Post by Anatine Duo on Fri Jan 27, 2017 1:23 pm

    So I've been trying loose laminates on a scrap Barnett crossbow... trying to see if I can get a narrow, high braced unit for light arrows, but I'm running into issues.  I can only fit 2 FG tension bars in it, and I keep breaking the inner bar.  Also, when braced, the inner bar only makes contact at its tip, which gets worse of course when cocked.  I've tried two lengths of inner bar, roughly 3/4 the outer and 1/2.  I feel like it might survive at 7/8 the outer but it seems that would be clunky

    Is there a general rule about the ratios between the laminates?  Is two layers a dead end?

    scratch

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    Re: loose laminate issues

    Post by c sitas on Fri Jan 27, 2017 2:13 pm

    Anatine, I don't quite understand what you have but, the one I built is this way. Main beam is 30 inches long the next piece is 23. Two pieces total. I have them fastened together pretty good in the center with a double heavy heat shrink on them .Then two more binders on each side of the center.And being so strong it will want to remain straight instead of following the main bow. I thinned my second bar down to a taper in order to make it follow the 30 inch piece. You know, with the inner piece only 23 inches long ,it's way stronger than the 30  inch piece. If I'm not mistaken I think Ken on here uses pretty much the same thing . I've been known to make a mistake before though.
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    Re: loose laminate issues

    Post by Anatine Duo on Fri Jan 27, 2017 7:29 pm

    Thanks C,

    I was afraid it might come down to thinning the inner piece... sounds like work!
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    Re: loose laminate issues

    Post by kenh on Fri Jan 27, 2017 8:46 pm

    How long are your lams, Anatine?  I have one 28" and one 16"; at 3" brace they touch everywhere.  I'm getting more than 250# draw at 12".  There probably is some mathematical relationship describing the perfect lam relationships regardless of material. But math never was my strong suit.  

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    Re: loose laminate issues

    Post by c sitas on Fri Jan 27, 2017 9:24 pm

    Anatine,What ever you decide, if you have to do any tapering or grinding or sanding, be advised to protect "firstly your lungs,then secondly your skin from the dust.I'm an old corvette lover and can tell you that working with fiber glass can be murder. If you don't protect your self from the dust ,you might wish you were dead. It'll give you a case of the itches like you never had in your life. ALSO, be very careful of slivers. You'll get them but ,you can't see them,and they pick. Use leather gloves for the fine sanding. If you prepare as I say ,---not so bad. BUT I just want to make sure that you know what is involved for grinding ,sanding etc.It may sound slower but if you take some coarser sand paper and go by hand block, but  you'll go a long way in keeping the dust to minimum.Always use a block to support the paper. Nuff said.You'll have to make the call here as I can't see what you have.I try my best to keep the bow in a nice arc, like it was before you added the second piece.Sorry for the preaching.
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    Re: loose laminate issues

    Post by Anatine Duo on Sat Jan 28, 2017 3:08 am

    Hi Ken glad you showed up... It's your data that inspired this experiment!

    The lams are 26" and 20" and I am trying to draw nearly 14". 

    Ok so I'm going to try some math here...  The moving part of the limbs shall be the length measured from the string nock to the tiller on the outer lam, and from the tips of inner lams to the tiller.

    For Ken's we see approx 25:13 (going by numbers and photos) or 1.9 to 1 and nice contact along the lams at brace, nice poundage at 12" draw

    On my last attempt I had 1.4 to 1 and contact only at the tips at brace,  broke when drawing.

    On my first attempt I had about 2.2 to 1 and it started making funny sounds at full draw (13.8") but overall this prod was only 24" to start so much more highly stressed.  I have the failure on video, will post soon, after shortening.

    c. sitas has about 1.35 to 1 (haven't seen how wide your bridle area is) and you had to thin the inner lam to get a nice curve.

    Well ironically I had been going to shorten my inner lam but instead went the other way at the last minute, thinking I could always cut it shorter (NOT!  splintered to bits).

    Going out on a limb (teh heh) and predicting a 2:1 ratio will survive.  Considering this drawing

       http://vignette4.wikia.nocookie.net/crossbow/images/3/34/8_laminate_bow.png/revision/latest?cb=20110420064855

    that makes sense.  The lams are equal parts.  Using only 2 threw me off.

    C. thanks for the FG warning, I have experience with many laminates and huge amounts of silica, but every thread should mention the importance of protecting oneself (and family... don't bring that dust into the house on your clothes).  I use P100 filtration and wish I had used it when I started working as a kid.

    PS I blew up 2 more configurations this morning... it might be too much to ask of the material even with 25.5" nock to nock.


    Last edited by Anatine Duo on Sat Jan 28, 2017 9:52 am; edited 1 time in total (Reason for editing : ps)
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    Re: loose laminate issues

    Post by kenh on Sat Jan 28, 2017 7:22 am

    Yeah;  I'd say you are pushing the boundaries by trying to draw more than half the limb length.

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    Re: loose laminate issues

    Post by c sitas on Sat Jan 28, 2017 7:53 am

    Anatine, I don't feel you'll draw 14" with a 26" prod.  I feel I'm at my max of 13.5  using 30" prod. My stuff is slightly different. I'm 3/8" thick and 3/4 wide. Very stout stuff.
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    Re: loose laminate issues

    Post by Anatine Duo on Sun Jan 29, 2017 1:12 pm

    Yes you guys are right I can't get that draw length with this material in this thickness!  I tried it many ways... giving me a bucket of busted unidirectional f-glass.

    I did get stable results with a 27.5" ntn outer and a 13.75"  thickness tapered inner  (thickness tapering wasn't as bad as I anticipated... I was reluctant because if I was willing to thickness taper I wouldn't pick the loose laminate technique) 

    The problem it seems is in the material.  It is not stiff enough for this job, as together the two laminates draw 35lbs (yes 35 pounds, not kilos, not 135lbs ) LOL

    So, it gives 155fps with 200 gn bolts (the string is pretty heavy, just something I twisted up quickly) at 6"brace height.  Another configuration used nearly full length inner lam and that gave 175fps but looked pretty sketchy.

    Hope this saves someone some time!  Now, what am I going to use these bars for?

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    Re: loose laminate issues

    Post by c sitas on Sun Jan 29, 2017 3:47 pm

    Anatine; I can,t understand what type of fiber glass your using.My main prod is 30" By itself it will yield 140 pd. pull. Add my second one at 23 tapered, and i'mm over 225. At 13 inches pull. If you want to try something else ,try three pieces of 3/8" fiber glass fence post.Held in a diamond shape. Obtained at almost any hardware or farm store for about 1.00 each . Three will pull about 145#, at 30" long at 14 inches draw.I killed a nice whithetail fork horn with that this deer season.At about 22 yds, had a clean pass through.
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    Re: loose laminate issues

    Post by Anatine Duo on Mon Feb 06, 2017 12:44 pm

    AHA!  Some interesting results:

    I took the thickness tapered inner bar off and draw went to 25lb @ 14".  So all that thickness tapering only got me 10lb (keep in mind this is with 6" brace

    I filed out the mortise on the old Barnett so I can get 3 of my .5" by .25" tension bars in, same length outer as before, 2 evenly spaced inner, taped them in place (this might be significant as I hadn't secured the bars to each other previous) and now it draws 75lb at 14" with 1" of brace, no tapering required.    

    I have some boat canopy slats now to try for a full width limb but I had wanted to experiment with the cheap stuff first.  Good thing too as I broke so much of it!  So with 1" available in the mortise I believe I'll be getting well over 150 lb if the slats are similar in material properties.

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    Re: loose laminate issues

    Post by c sitas on Mon Feb 06, 2017 8:25 pm

    Anatine ; I think you've caught on here. The taping is all important.Tape where it looks like you need it.Once your set to try the scale, just come on it slowly, and watch close.I keep looking for the arc of the bow  to stay fairly smooth. No abrupt changes.Keep in mind also, lower brace is maybe a little more power or zip but, is a little noisier. I, without looking ,think I might be about 2.5 to three" brace.  Good to see your hanging in there. I recently found a good buy on E bay. Flat glass rod, 3/8 x 7/8" 54" long . Cheap also. Stop and think when your doing this stuff. Don't go by something you heard. Prove to yourself. Take my word for it, it's way cheaper.
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    Re: loose laminate issues

    Post by Anatine Duo on Wed Feb 08, 2017 3:35 pm

    With the current 75lb draw:

    255 gn arrow at 193 fps
    146gn at 226fps 

    I think more speed is available by lightening the tips, using better wraps instead of tape, and reducing friction between the laminates.  Also the string is for the full power 150lb lath so it's heavy, and I twisted it out of some waste fiber from a construction site so it's no fastflite.

    -11 C not sure what the effects of temperature are

    Already approaching the power of my "asian barnett clone" at about half the draw weight though I'm sure the clone was better with the heavier arrows.  More to come!

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    Re: loose laminate issues

    Post by c sitas on Wed Feb 08, 2017 5:23 pm

    Anatine, If I may ask ,where do you call home? I don't use fast flight or any of the newer dyneema fibers for crossbows because there is absolutely no stretch. You know what happens to a bow if it would be accidently discharged without an arrow to eat up the energy. That's why I use dacron . Most of the time there is just enough stretch to save he bow. I still would not reccomend doing so for fun. Take my word for it, I don't care whom you are ,you will dry fire. I do use the fast flight on my compound bows, as I make all my own strings. I made an electric winder so I could make my strings under about three hundred pounds of pull..  I leave the string stretched over night before I finish it. That is common practice now. By the way I don't think that -11 c is good for any thing .except ice fishing.
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    Re: loose laminate issues

    Post by Anatine Duo on Wed Feb 08, 2017 7:27 pm

    Home is Muskoka, Ontario, Canada.

    I agree with you about the dry fires... I had been researching for a new crossbow and I kept seeing "anti-dry-fire" and I thought to myself, why would I need that?  

    Soon after I had my first dry fire in 3 decades of crossbows!  Sheesh!

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    Re: loose laminate issues

    Post by c sitas on Wed Feb 08, 2017 8:41 pm

    Antine, I'm 74,and Ive been shooting competition archery and hunting for about 65 years. AND I'll still do it .That is why I try to cover myself.I have built 4 compound crossbows out of spare parts. Also three stand type crossbows. I constructed each with their own homemade trigger . Each time trying a different type but, I incorporated anti dry fire on all of them. Very easy to do. I've only had to use it once. Kind of crap to get the string free again but, it's still better than the other choice.You have access to string materials where you live?
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    Re: loose laminate issues

    Post by Anatine Duo on Thu Feb 09, 2017 4:49 am

    I bought a spool of Dacron but have been making Flemish-style strings out of the webbing that lumber is often strapped with.  It doesn't seem to have much stretch.  I wax with beeswax and serve with nylon.  Some of my paracord is polyester and the the inner strands get used too.  

    Did you post your anti-dry-fire here on thearbalistguild?

    The reason I may use one of the high tech fibers is to get the numbers the commercial crossbows advertise!  

    It appears much easier to get commercial string materials here than thick fiberglass bars.  Shipping from the USA is nuts.

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    Re: loose laminate issues

    Post by c sitas on Thu Feb 09, 2017 7:40 am

    Sounds; like your all set. Each area seems to have it's own little quirks eh?No, I never posted anything here.I'm photo challenged.Don't have the stuff to do it. Really all you need is a strong top cover over the latch area.My locks all use 1/8" steel. Then take a piece of 1/4" x about 2 and drill it so it is nose heavy. The nose is toward the roller and would fall down by itself to be lower than the string,almost touching the roller, thus catching the string. If an arrow is present it just hold the catch up and out of the way. Anything that can contact the string is polished perfect smooth. It pivots on a 10/32 screw.  If you don't catch on maybe, I could have someone around here send you something with email.
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    Re: loose laminate issues

    Post by Anatine Duo on Thu Feb 09, 2017 3:17 pm

    Your description gives me a ton of ideas!  Thanks...  I think anti-dry fire deserves its own thread.

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    Re: loose laminate issues

    Post by c sitas on Thu Feb 09, 2017 3:33 pm

    Anatine, just one more nudge. Just think of catching the string by the leaver I mention . It'll get pinned between the lever and the top of the lock case. To release it, just recock  the string. Alot of the factory deals almost become a song and dance to get  things back to normal.
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    Re: loose laminate issues

    Post by Anatine Duo on Sat Feb 18, 2017 6:41 pm

    My optimizing gave a tiny bit more speed with the 255 gn arrow giving 200fps but the the 146gn is stable at 224fps, which is interesting... going to make some even lighter arrows and see how close to dry fire it is.

    After optimizing, the draw weight is maybe lighter (hard to be accurate on a bathroom scale) or just smoother to draw.  Inner lams are no longer cutting into the outers, plus I don't have to listen to squeaking tape.

    Also these speeds are now with serving so that might have cost a couple fps.

    I really don't like the look on the Barnett so it will get a different limb and the looseleaf will go on a scratch built.

    I'm curious now about some hard width tapering using the 1.75" wide boat bow glass.


    Last edited by Anatine Duo on Sun Feb 19, 2017 4:03 am; edited 1 time in total (Reason for editing : adding image)

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