ILF Questions

[Turkeys Fear Me]

Originally posted by Blake Dustin Adams:

It might surprise you just how strong some bolt are when being pulled.  Working as a machinist, working on cars and other mechanical objects most my life, and now being a helicopter mechanic I have seen a lot more bolts sheared than I have broken in any other way.

Also when I saw all that connects a 2,000 HP turbine engine to an input module is a few (3-6 depending on model) approximately 6mm bolts and a flex pack, and they fly without being replaced for hundreds of hours, it makes you a believer in high grade bolts.

Seeing that there really isn't any lateral stress on the limb bolt, any talk of failure, as long as you have the proper strength depth, is kind of overblown it seems.

[Bob Morrison]

The ILF bolt does have some lateral stress to them, the farther a bolt is backed out the more stress on that bolt. I have not seen it happen yet but it could be possible to bend the bolt, I don't think you could ever break it.

[Ray Lyon]

I've not been to Africa, nor hunted anything biggger than elk, however I'm wondering about the need for a 90 to 100 pound bow for even the biggest game in Africa???? Howard Hill and Bob Swinehart were tackling elephants with 100 pound bows that were not using the same materials nor quality of design of todays bowyers. I'm speculating a little here, but thinking along the lines of a set of Dryad Epic static limbs at 80 lbs. with fast flight string and weighted skinny carbon arrow (1,000 grain plus)with Grizzly 160 broadhead would be no less potent than what was used back in the fifties and sixties by Hill, Bear and Swinehart.

[Ray Lyon]

oops, I meant to add extreme FOC to my parameters

[Steelhead]

I dont think thier would be any problem with that setup for Africa and Cape buffalo or lion.As long as your arrows are flying true and properly reinforced at the business end for dangerous game it would be a wicked setup.Probably step up the broadhead to a heavier Abowyer,Ashby 300 gr. or grizzly 190 grain or maybe a steelforce African head.Those are some thick heads with tonto style tips.

I think Hill killed one of his elephants with around a 125# bow?Might have been his 1st one with a very long arrow from what I remember.

[Turkeys Fear Me]

Originally posted by vermonster13:
You would be better served going with a conventional takedown for the 90-100 limbs. The ILF risers won't be rated for that much weight, even the metal ones. David set a limit of 70# or so on his Dalaa risers I believe.

I've been thinking a lot about this statement over the last couple days, wondering why DAS might have set a weight limit on his riser and I think I may have figured it out.

If you look at the way the Dalaa is desgned, because of the position of the thumbscrew, the area of the limb pad that is under the most stress (under the limb rocker) is extended past the beefy part of the riser.  There is no reinforcement under that area so the thinner limb pad (with a hole in it for the thumb screw) takes all the stress.

 


On the other hand, notice that the ILF connection is integrated into the riser so the stress is carried on the beefy part of the riser, not on a pad that is "cantilevered" beyond the beefy part of the riser.
 

 
 
 


It's understandable (at least to me) why there would be weight restrictions on one design, and not so on the others.

Make any sense?

[Turkeys Fear Me]

Even if you look at the ILF target risers, the always seems to be reinforcement under the rocker.

Hoyt

 

Samick

 

Bernardini

 

[Bob Morrison]

In heavy weight limbs, most of the pressure is on the main limb bolt. The limb acting like a pry bar. A steel insert and 5/16" bolt with 1/2" threads will hold just fine. taped in to wood and its going to need to be much longer. This is the reason most bowyer will use larger steel inserts, we use 1/2" od x 1" and a courser thread stainless insert on our wood riser. Our metal is less than 1/2" because it is in aluminum, but still has a stainless insert (stronger than the aluminum) to make it so we can adjust poundage or tiller with bow strung and not glaud and lock the bolt to where you can not remove it.

[stik&string]

Thanks for this post, it has been very useful and informative.

[Turkeys Fear Me]

Originally posted by Bowbldr:
In heavy weight limbs, most of the pressure is on the main limb bolt. The limb acting like a pry bar.

True.  However with the limb acting as a "pry bar," the limb bolt holds one end of the lever (pry bar) down, exerting more pressure on the fulcrum which is directly under the rocker of the limb.  In the case of the thumb bolt system, this would be the weakest point.

Think of it in terms of a claw hammer pulling out a nail.  The nail is the limb bolt, the round part of the claw is the limb rocker and the hammer handle is the limb tip.  The board that the nail is in is of course the limb pad.

If the nail pulls out easily, the round part of the claw doesnt put much pressure on the wood.  If however the nail is stuck (like the limb bolt), the harder you pull on the hammer handle (as in heavier weight limbs) the more damage the hammer does to the wood.

So, with the limb pad unsupported under the rocker, (cantilever) if anything is going to give, it's going to be that pad, especially if there is a hole through that section.

Make any sense?

I'm not saying that it will ever be an issue with normal weight limbs, I'm just speculating as to why DAS would have put weight limits on his riser.  This would be the only logical reason in my mind.

[Bob Morrison]

In an ILF limb the rocker area is the thickest part of the wedge taking care of that problem in the limb. and I doubt that the plate in the das is going to bent either, at worst that is all that could happen it would bend and not break. I would be more concerned in the bolt pull out of the riser or the end of the limb around the bolt letting loose and breaking. This is not a problem in lower pounds 70-. heavy will need to be thicker in the bolt area, and the bolt may need beefed up may grade 8. and as long as possible in aluminum thread holes.

[Turkeys Fear Me]

You are probably right Bowbldr, I don't happen to think it would be an issue either.  I was just trying to speculate as to why, as vermoster13 said, DAS would put a weight limit on his system, and that is the only thing I could think of.

You have to think about something when you're in a treestand...

Makes for an interesting discussion though.

[Bob Morrison]

I came up with most of my bow design sitting in treestands.