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Crossbows - Everything about Building, Modding, and Using your Crossbow Gear

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+2
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jrdallmann
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    RDT crossbow project

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    jrdallmann
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    Post by jrdallmann Tue Oct 28, 2014 6:10 pm

    First topic message reminder :

    Hello folks!
    First of all, I'm from Brazil, so sorry my bad English. I'm planning to build my first crossbow on next vacation, which begins within about a month. I've been doing a lot of research about it for the last few months. Since I own a car shop, I got everything I need to build my crossbow. 
    I'm inspiring myself on patandjali's rdt model. Today I started to search for components for my crossbow. I found a spring leaf from an old Willys which will be my prod and removed the valves and the valve guides from a VW engine head to use as axle and sleeve for the cams.

    RDT crossbow project - Page 2 Img_2011

    RDT crossbow project - Page 2 Img_2010
    The leaf is 40" long

    It's not a project I wanna do in a hurry, so I'll take my time. I'm open for suggestions.
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    Post by ali.j Fri Nov 21, 2014 5:47 am

    today...

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    Post by jrdallmann Mon Dec 01, 2014 4:04 pm

    Hi guys. My vacation is coming soon, so I'm preparing everything to start working on my project. I already have almost everything I need. But, today, while working at my garage, I've thought about something.. what if instead of using an aluminum plate and working on it to build the cams, I use a pulley like the one below? I'd just have to work the "teeth" off and cut it to make the "entrance" for the string. what do you guys think?

    RDT crossbow project - Page 2 Polia-original-do-comando-vw-motor-ap-16-18-20-gol-parat-14402-MLB233374678_7914-O
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    Post by ali.j Tue Dec 02, 2014 3:06 am

    no. Not working. You just have to like me, you use cams. meterial appropriate for made cam is al Alloys. no 5000 or 6000 or 7075.

    this clip It may help you in making.
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    Post by jrdallmann Tue Dec 02, 2014 7:50 am

    So the bowstring material kit i've bought just arrived yesterday. Since this will be my first time at making a bow string,I just want to clarify something.. In the picture below, the purple thread is dacron b 50 while the black one is serving material, right?

    RDT crossbow project - Page 2 Img_2010
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    Post by Hermit Tue Dec 02, 2014 8:04 am

    Hi Jrd,Ali is right your gear wheel won't work.A gear wheel has to rotate eccentrically(in balance,like a car wheel).Acam rotates eccentrically(out of balance)it would be just about impossible to modify a gear wheel,you will have to make the cams yourself.
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    Post by jrdallmann Tue Dec 02, 2014 2:55 pm

    I got it, haven't thought about that.. and what about the threads?
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    Post by Hermit Thu Dec 04, 2014 9:17 am

    Looking at my spool of Dacron(It's grey in colour)I would say that the purple is the Dacron.
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    Post by jrdallmann Fri Dec 05, 2014 7:55 am

    ali.j why are there two holes in the center of your cams?
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    Post by ali.j Sun Dec 07, 2014 12:10 pm

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    Post by jrdallmann Mon Dec 08, 2014 5:50 pm

    hey ali.j, can you tell me why there are 2 "center holes" in your cams?
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    Post by Hermit Mon Dec 08, 2014 7:23 pm

    The central hole is for the cam pivot pin,the off centre hole is for the string anchor pin.
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    Post by hullutiedemies Tue Dec 09, 2014 2:28 am

    jrdallmann wrote:Hi guys. My vacation is coming soon, so I'm preparing everything to start working on my project. I already have almost everything I need. But, today, while working at my garage, I've thought about something.. what if instead of using an aluminum plate and working on it to build the cams, I use a pulley like the one below? I'd just have to work the "teeth" off and cut it to make the "entrance" for the string. what do you guys think?
    ..

    You could use pulleys. Here is one apparently succesful build for example :
    https://thearbalistguild.forumotion.com/t774-compound-project

    but it is going to be a bit different design.
    Force-draw curve will not be as efficient. But you can have longer power stroke since pulleys can turn multiple revolutions.
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    Post by jrdallmann Thu Dec 11, 2014 5:50 pm

    thanks for replying flinstone, but i'm not gonna use that kind of pulleys. Today I finally startes my crossbow. I decided to start from the most difficult part: cams. I mean, it's not that difficult, but toilsome. I wasn't able to finish them today because I only have time to work on my crossbow after job, and december is madness in my auto shop. However, is going well. I'm just a little bit worried because my aluminum plates are not exactly 8mm thick, they're little thinner, around 7mm, but  I guess that's no problem. Just to make sure, what is the thickness (approximately) of a crossbow string?
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    Post by jrdallmann Tue Apr 21, 2015 12:43 pm

    hey guys, I had to put my crossbow project aside for a while due to college, work and stuff. Yet, I finished my first cam and would like you to take a look and tell me waht u think, I'm a little worried about the thickness..

    RDT crossbow project - Page 2 Img_2011

    RDT crossbow project - Page 2 Img_2010

    PS: not finished, i still have to drill it and do the second little cam
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    Post by ali.j Thu Apr 23, 2015 3:31 pm

    Very Happy



    shooting test. 165 lbs/300 fps  Laughing






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