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    Question about prod specs

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    Daniel Levesque
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    Question about prod specs

    Post by Daniel Levesque on Mon Jan 16, 2017 8:43 am

    Hello everyone,

    For now at least, I give up the idea of working on a wood prod. I'll build a composite one in the future though.

    So, I wanna build a spring steel prod (there's a metal shop nearby who sells 5160 springsteel flatbars...lucky me Smile )

    Anyway, I want to use the same tiller I was to use with my wood prod... it's quite massive but I'm a big guy as well. The draw length would be 12,5 inches (I'd say I'd brace the prod at 3-4 inches and the rest would be the power stroke. The prod should be 2" at the centre and tapered toward the knocks but I'm not quite sure how I should do it (I would work it carefuly with an angle-grinder and have someone at the shop to heat-treat it. In the final, I'd like the bow to be around 250-300 pounds of draw weight. I guess the prod knock to knock should be around 34-35 inches to be safe ?

    Any ideas about the specs ? I did some research but I'm still pretty much in the dark right now...
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    Re: Question about prod specs

    Post by OrienM on Mon Jan 16, 2017 12:18 pm

    Have you seen this? Probably a good place to start:

    http://crossbow.wikia.com/wiki/Plan_for_a_simple_leaf-spring_prod

    Don't lengthen the prod if you want high draw weight out of 1/4" stock; the above design produces 150#, but could be widened and/or shortened a bit overall to increase the pull.

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    Re: Question about prod specs

    Post by c sitas on Mon Jan 16, 2017 1:52 pm

    Orien, I made that design. only difference was I cut it out of an old crosscut saw.Made a eight piece laminate. Ended up heavy . It shot alright but had a real after shock.My lam ended up at about 225#.Ended up going to glass. Pretty much the same as Kenh built.Much calmer to shoot, and no after shock.Ken used 1/4" thick stock.That wiki is a good one ,it tells just about all there is on the subject.
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    Re: Question about prod specs

    Post by Geezer on Mon Jan 16, 2017 10:04 pm

    About prod shock (recoil) If you're getting lots of prod shock or recoil at the end of a stroke, try increasing the bolt weight.  If that doesn't help, a heavier stock can improve things.  Geezer.
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    Re: Question about prod specs

    Post by OrienM on Tue Jan 17, 2017 8:10 am

    I made a prod based on the wiki plan as well, but much shorter, and used it in this little crossbow: http://thearbalistguild.forumotion.com/t1249-my-second-crossbow-the-little-devil?highlight=little+devil

    This prod is only 15" overall, and pulls 150# with a 2" brace and 3" powerstroke. It deals well with a heavy projectile, but shoots rather sluggishly overall, which apparently is fairly typical of a steel prod. The bow is also rather 'kicky', even with heavy bolts.

    With old steel prods you often see very short draw lengths used, usually about 2X the brace height...I'd be careful about going much past that, proportionally speaking.

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    Re: Question about prod specs

    Post by c sitas on Tue Jan 17, 2017 8:37 am

    For my self,after shooting both types of material ,glass and steel,I'll take the glass. Just my opinion though.Not a purest either. I don't use factory prods either.The steel one I made kicked like a rifle. I think what I use is called pulltruded or something on that order. It's factory made flat stock. I've even had great luck with glass fence post. Not hard to get over 200#  there. Orien, that bow you built and showed is a work of art. Has all the right qualities.Being an archer is my problem. I build to get shooting. I make all types and use mostly crap left behind from someone.
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    Re: Question about prod specs

    Post by OrienM on Tue Jan 17, 2017 9:26 am

    Thanks! Personally I'll take a wood/sinew prod over a steel one...I could never quite get comfortable with any of my steel-prod efforts, and already had some experience with simple composites from making archery bows. Wood/sinew fails in a different way than steel, folding up rather than snapping...longer draw lengths are do-able, and the prods are light and snappy-shooting.I think draw weights up to 250# or so are pretty do-able, above that horn bellies are probably required.

    They certainly take much longer than steel prods to make, though, and can't deal with anything like the super-high draw weights that steel can potentially provide.

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    Re: Question about prod specs

    Post by c sitas on Tue Jan 17, 2017 10:33 am

    Orien, I surely envy you and your abilities . A wooden prod would surely be the way to go. Light ,fast ,and quiet. Never shot crossbow with one but over time I've had my share of stick bows and compounds.I'm 74 but I still can get excited over a deer. With some sort of weapon in your hand , the hunt is on.It's even fun to hunt with a fence post.
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    Re: Question about prod specs

    Post by Daniel Levesque on Tue Jan 17, 2017 11:46 am

    You're amazing guys !

    Orien, I'll certainly try a wood/sinew prod instead of wood/rawhide (which is no good) but I'll back off a bit on the draw weight... going to 300 pounds was waaaay too much for my (in)experience with crossbows anyway. I tried I guess. My next try is going to be around 150 lbs or so (sounds do-able).

    For the steel prod, I want to give it a try anyway (I'll probably build another tiller for this one since woodcrafting has been my addiction lately). I found a place where I can get 8 foot flatbars of 5160 springsteel 2" x 3/8"... I'm still waiting for the guy to give me a price though... I just hope I'm not going to be disapointed.
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    Re: Question about prod specs

    Post by OrienM on Tue Jan 17, 2017 12:33 pm

    Yeah, I don't mean to get off-topic into composites!

    I'd say 3/8" thick steel will work better than 1/4", especially if you want to get 300# and add a bit of length to the prod. Nice that it is new flat stock, not old springs with their holes and potential stress cracks.

    You're going to want to bend some deflex into the prod before heat-treating, too...maybe 3" or so of deflex for a brace height of 4". It makes for a fairly low initial string tension, but a much safer prod; with stiff enough limbs, draw weight still goes up quickly as the string is pulled back.

    BTW the same general ideas (stiffening limbs, adding deflex, and using a proportionally short draw length) seem to be beneficial with all-wood and wood-sinew prods, too. The belly wood can fail (or steel bows can explode!) if limbs are pre-loaded too much.

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    Re: Question about prod specs

    Post by c sitas on Tue Jan 17, 2017 12:55 pm

    Daniel, I found some on  knife makers sight. He wanted $2.85 a foot for 5160 spring steel. If he had to ship apiece over 48" ,he wanted an extra 10 dollars .I imagine for some extra boxing . Didn't see anything for freight,but that would vary by lo-cal.
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    Re: Question about prod specs

    Post by Daniel Levesque on Tue Jan 17, 2017 1:22 pm

    Wow... that's awesome price-wise, it's cheap enough for me at least Razz

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    Re: Question about prod specs

    Post by c sitas on Tue Jan 17, 2017 3:51 pm

    Darn it Dan, I my haste to type I screwed up. It's supposed to be 12.85 NOT 2.85. Dumb me .Sorry to get your blood moving.
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    Re: Question about prod specs

    Post by Daniel Levesque on Tue Jan 17, 2017 7:19 pm

    Oh..noooo !! I'll still probably buy some, maybe not as much.

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    Re: Question about prod specs

    Post by c sitas on Wed Jan 18, 2017 11:12 am

    Stop and think , two feet is less than half of ready made.But, you have to add shipping and that depends on where you live. Corse, you have to have shipping no matter what or where  you buy.
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    Re: Question about prod specs

    Post by Daniel Levesque on Wed Jan 18, 2017 11:24 am

    Thought about that. I think I'll just buy a premade prod from slobows. I can get one for about 90 $ (CAN dollars sucks) including shipping rate. If I buy the steel, I'll need 3 feet at least, shape the prod and have a machine shop to heat-treat it (including additionnal charge for that), It 's bound to get pricey anyway.

    I'll still buy a couple of feet of springsteel to forge some knives though Wink
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    Re: Question about prod specs

    Post by Daniel Levesque on Wed Jan 18, 2017 12:21 pm

    Sorry all, just one more question here :

    I know that for steel prod, the top won't be narrowed down, it'll just be flat and it's the bottom from center to tips that will be narrowed (kinda like an inverted pyramid) to reduce tension and friction for the string on the tiller. Is it the same for a wooden prod or should it be narrowed down equally (top and bottom will be the same) ? (my guess would be NO because of uneven tension (possible torsion) along the bow but since i'm new to this, I prefer to ask).

    BTW, sorry if the structure of my sentences seems off a bit sometimes, French is my main language.

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    Re: Question about prod specs

    Post by c sitas on Wed Jan 18, 2017 2:35 pm

    I'm not a expert but,  have never seen this narrowing as you mention for a wooden bow. All the final shaping is called tillering,and that is to make all the tension equal,and make the string come right down the center of the mass.Some of the shaping you are mentioning for steel serves the purpose of  kind of jacking  the string up to relieve pressure on the rail of the stock so you can make a strong mount for the bow.  ---I think .If you would draw out a full size picture the way wiki tells you, you would see what I'm trying to say. Pay real close attension to the way they lay it out to start with.   Orein would know sure.He makes wooden stuff. There are others here also.
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    Re: Question about prod specs

    Post by OrienM on Sat Jan 21, 2017 9:03 am

    Hey, apologies for my slow response; my computer was in the shop.

    Personally I've been making my wooden prods with a shape very similar to steel ones. They're asymmetrical; the upper edge of the prod is flat, the bottom side curved/tapered.

    It does induce some limb twist, but helps a great deal to reduce string pressure on the tiller. I actually think twist is inevitable in crossbow prods...no matter what you do, you'll still be drawing the bow off-axis. A moderate asymmetrical profile seems to be a good compromise; the other option is to increase the angle (forward tilt) of the prod in the tiller, which also increases limb twist and can cause dry-firing, as well.

    With steel, you can actually lift the tips even higher, making a concave upper edge; it improves string geometry to a point, but also increases twisting forces at the prod mounting. Go too extreme, and you can split the tiller, or tear out the bridle holding the prod in.
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    Re: Question about prod specs

    Post by OrienM on Sun Jan 22, 2017 12:12 pm

    Found this old thread here with some excellent info about designing prods; it's focused on wooden prods, but also delves into steel-prod design: http://thearbalistguild.forumotion.com/t1387-wood-prods
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    Re: Question about prod specs

    Post by Daniel Levesque on Mon Jan 23, 2017 6:57 am

    Thanks Orien, I already saw that link (very good info) but I was more interested to get your views on a flot top prod. I wasn't so sure about the limb twist but since you've done it before and it seems to work, I'll give it a try. I just didn't want to invest time in something that would be doomed to fail from the start. I'll begin work on my prod (sinew backed hickory prod) this week. I'll keep you guys updated. Thanks again for your good advices.

    By the way, I know hickory is a solid wood for backings but it performs so-so for the belly. What kind of wood should I use if I want to make a laminate prod with a hickory backing (and please, don't tell me Osage Orange, it's not available where I live) ?
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    Re: Question about prod specs

    Post by OrienM on Mon Jan 23, 2017 7:32 am

    Unfortunately I don't have much experience with wood-backed laminates; I've made a few archery bows of Ipe wood with bamboo or hickory backs that shot well.

    Some of the better bowyery woods (besides osage Wink) would include mulberry, elm, black locust, hickory, and hophornbeam (AKA ironwood). Ipe is also good (its portugese name is Pau D'Arco, or bow wood), but it's also incredibly dense...I don't know if it steam-bends very well, either. Hickory can be a very good choice, but in my experience it varies quite a lot...a particularly hard, heavy example can make an excellent bow.

    IMHO there's no real reason to laminate a prod if it will be sinew-backed as well. The sinew takes over the function of backing, and is much stronger in the job than any wood, or even bamboo.
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    Re: Question about prod specs

    Post by Daniel Levesque on Mon Jan 23, 2017 7:57 am

    Understood ! Thanks for the advice. Wink

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