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Retrofitting Longer limb bolts

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Retrofitting Longer limb bolts

Old 04-15-2004, 12:22 PM
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Nontypical Buck
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Default Retrofitting Longer limb bolts

One thing I really like about older bow designs was the use of longer limb bolts to allow one to simply relax limb pressure by unscrewing the bolt until the string/cable(s) relaxed, eliminating the need for a bow press to do work.

I just learned that Newberry bows apparently does this, which is a big plus, in my book. I wonder why more manufactureres don't, not doing so makes little sense to me.

However, I'm left wondering why one can't simply have a qualifed machinist lengthen the limb bolt hole a bit and install longer bolts? If there is no big issue in doing so, how much longer of a bolt would it take to accomplish the desired no press needed feature?
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Old 04-15-2004, 01:23 PM
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Default RE: Retrofitting Longer limb bolts

It would depend on the design of the riser as to the possibility of "lengtheing the limb bolt hole". The process of doing this to a bow's riser would be a very tricky task and doubt if anyone would want to tackle it. The diameter of the drill must be smaller than the threads of the tap and I'd bet that you would damage the original threads while trying to maintain proper alignment necessary to avoid damage. Damaging the original threads would mean using a helicoil to repair it and if the riser wasn't wide enough to allow the use of a helicoil,,, you'd be SOL
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Old 04-15-2004, 01:40 PM
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Default RE: Retrofitting Longer limb bolts

Couldn't you just fill the hole with JB Weld and start all over?

I figured it'd be a very tricky process, but wanted to through this out for discussion anyway.
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Old 04-15-2004, 01:49 PM
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Default RE: Retrofitting Longer limb bolts

Why not just drill the hole to the desired depth and larger diameter and rethread it? Of course you would then require a larger diameter bolt. With a drill press it shouldn't be a huge deal. Heck you could drill all the way through the riser and use bolts as long as you want.
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Old 04-15-2004, 01:58 PM
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Default RE: Retrofitting Longer limb bolts

I guess it'd depend on how thick your riser was and if it would weaken it significantly by doing so. Also, you would want to make sure you don't also need to drill the limbs out to accomodate the wider bolt...

But I had that thought as well.
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Old 04-15-2004, 02:10 PM
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Default RE: Retrofitting Longer limb bolts

Well we are talking thousands of an inch here. I wouldn't think you would want to get real carried away when you were drilling it out. On many risers there isn't much extra to work with. You do make a good point though. You might run into issues with the hole in the limb being too small if you drilled out the riser.
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Old 04-16-2004, 12:48 AM
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Default RE: Retrofitting Longer limb bolts

With as much preload on some of today's bows, I'd worry about the limb rockers having enough height to be able to clear the limbs from the ends of the limb cups when letting the bow all the way down.
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Old 04-16-2004, 08:14 AM
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Default RE: Retrofitting Longer limb bolts

Personally I don't think I'd want to second guess the engineers who designed the riser. Maybe you're looking to have a riser snap at the limb bolt holes. There's a lot of stress on that hunk of aluminum. Years ago I had one come apart and hit me in the head. Doesn't feel good and almost makes ya feel like NOT drawing a bow for a while.
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Old 04-16-2004, 11:50 AM
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Default RE: Retrofitting Longer limb bolts

I once saw a PSE compound bow that a local machinist/bowhunter did extend the limb bolts for the purpose of relaxing the bow's limbs.

He machined the limb bolts out of high-grade steel. They were machined all-thread bolts and were slightly tapered at the outboard end, unthreaded, and shaped so that he could tighten the bolts with a small wrench. The bolts did (obviously) protrude but he had rubber sleeves over the exposed ends.

Keep in mind though; the limbs were longer (longer ATA) on his bow than most bows of today, and the string was attached to "teardrops." He said the system worked well. I cannot say it actually did or if he ever had tuning or breakage problems.
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Old 04-17-2004, 03:01 PM
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Default RE: Retrofitting Longer limb bolts

Its not as simple as that, with the current limb angles you will break the limb at the bolt slot if you were to back it out even as much as the current limb bolts allow. What will happen is the notched out area of the limb will eventually contact the limb bolt and splinter the under side of the limb.
BD
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