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Tuesday, 7 February 2012
Prod for New Crossbow
This is the prod I will be using temporarily on my new crossbow until I find a more suitable option.
The limbs were made of the front end of cross country skis. The cams were made of two roofing plates as shown in the last video these should be found at any hardware store or roofing outlet. The brackets holding the cams were made of a thick gauge sheet metal (not sure of the gauge exactly), and the string of some yellow nylon rope (will be swapped out latter for something else was thinking of the pull cord from an old lawn mower). The riser made of wood not sure what kind. Hope this helps anyone looking for prod options this cost about $10 to put together and is about 50lb draw. I may wrap the limbs in fibre glass and resin later to try and make it stronger. I will post any and all results
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You might want to correct "cams" to "pulleys", since cams have an offset center(hence the name - excentric cams) and have a unique force/draw curve that rises and drops...while pulleys simply give you a mechanical advantage over a load.
ReplyDeleteWrapping limbs in fiberglass won't help...in fact it will just make them weaker...do a search on "Laminated Bows" and how they are made...we use unidirectional fiberglass prepregs and some serious epoxy...it's a whole technology. ;)
You are right on the cam/pulley bit thanks :)
DeleteI must say it's a real advantage having someone as experienced as yourself viewing and commenting on my progress. I have said it before I am very new at this in comparison to others and appreciate the advice and knowledge of others and am glad I didn't waste my time and money wrapping this in fibreglass lol. I have attached it to an older crossbow and it makes for a nice little shooter.
No problem man. :) We never stop learning and I'm all for sharing what I've learned from other crossbow builders...take 5/6 years back...same thing...(calling pulleys - cams; and trying to use the 90/0(fiber oreintation) auto repair glass cloth/resin to make a bow :)))
ReplyDeleteSucks we can't post pictures as a part of a blog comment...I'd say more, but can't really do it without visual presentation.
Come to think of it, there was a guy on the tube who attempted a compound bow and then stopped by the forum where I posted some design notes...I'll go look for the topic and send you a link.
Ivo
...got it. :)
ReplyDeletehttp://thearbalistguild.forumotion.com/t424-i-need-some-helpwooden-compound-crossbow
If I were you, I'd cut a third of those skies off the tips, glue a reinforcement block (to the inner side of the limb) with a fade towards the center and cut a V in it like on the production bows. The pulley wheels are pretty thin, so the v gap in the now forked tips will not compromise anything(and the reinforcement block will give you another piece of mind).
If you do that, you will be able to take that bracket and mount it on the back of the bow.
[*back = side away from the shooter...outer; *belly = side towards the shooter...inner.]
The way it's mounted right now, the entire load is put on the screws/bolts used to attach it to the limb, but if you take it off and slip it *over* the limb, the load will be put directly onto the limb.
...you might even want to trim the bracket a bit and re-drill the axel holes (or even redo them completely - trust me it's worth it), now that the wheel center is much closer to the limb.
Don't know if this is going to come through, but here's a pic
http://i303.photobucket.com/albums/nn137/karman333/compundfork2.png
Also...Like in the topic, I suggest you lose the hole in the limb for mounting the string ends and use a yoke...I know there is a crossbow on the market(Parker Crossbows)that does it your way, but in the DIY world it's best to cover your ass with a riot shield. :P
Best of luck.
Ivo
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