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Andy Fletcher





Joined: 25 Nov 2009

Posts: 1

PostPosted: Sat 16 Oct, 2010 5:59 pm    Post subject: Scrap Yard source Crossbow Components         Reply with quote

Hi folks:

Need advice on fabricating a homemade steel crossbow.

I have the plans and specs of auto spring thicknesses for any bow to 400#, but I would settle for 120-250#. The string I will use is 6 cord flax and will make myself a string loop jig with wooden dowels. I know they use dacron now and that is an option. I came across sno mobile front sled springs of 5/32 thickness and an initial set of 3.6inches with nicely looped ends with 1/2inch holes for the spring retainers. Springs are 24inches.

The springs also come with a doubler spring of 12 inches, which sits over these main springs. These are for shock absorption I would guess, since the machines can slam down pretty hard in a jump. A problem is that there are two bolts holes spaced 3inches apart, and not the center single hole. My specs tell me that with a 5/32 spring and a taper cut on the prod of 5/8in to 1-1/2in, can get me a 126 lbs pull.

I was thinking of making use of the shock spring and use it has a doubler has it was designed, but cut them off an inch or so after the holes then bolt them together with self lock nuts. The doubler should reinforce the stress at the holes, at the same time giving me more stiffness of the bow possibly adding 20 or more pounds of pull.

The two holes of course makes it a problem in attaching it to the end of the stock. I would need to weld together a special mount bracket I presume. I have also carbon welding rod (blue) that I once used to repair car springs. I could weld shut the existing holes and drill out a center hole. Problem is I'm not sure if the effect of expanding heat would remove the temper of the rest of the prod which would be dangerous to me.

The other option is to use a car spring, which will give me a single hole, but I can't find a modern car (probably a compact) that has springs under 1/4inch thick.

Thanks for the advice.

Picture of the setup included.

Andy



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