Power Lams & Tip Wedges

[BK in Wisconsin]

Lets get some good info & discussions on Power Lams & Tip Wedges in one thread.
I'd like to move it to our new FAQ forum when were done.

So....who wants to tackle a few common questions:

1) What is a Power Lam?
2) What is a tip Wedge?
3) What do they do (simple answer)?
4) What do they do (complex answer)?
5) When should you use them?
6) When should you not use them?
7) How thick & how long?
8) How much is too much?
9) Other questions?

After someone answers, please feel free to add to or comment on their answers. And as always...ask more questions!

[Jess Stuart]

Well, I probably shouldn't be the first to go, I don't have allot of experience with them. My limited experience with both p/l and tip wedges have been positive to say the least.

What is a power lam? A short lam extending past the end of the riser by a few inches.
What is tip wedge? A short lam inserted at limb tip.
What do they do? P/L has the same effect as a longer riser, tip wedge stiffens the outer portion of the limb.
What do they do? (complex) They both provide a method of manipulating where and how much a limb will bend. P/L pushes the bend away from the riser, tip wedges push bend inward towards the riser. Tip wedges help to maintain a good string angle resulting in smooth draw.
When should you use them? Anytime you want to change the way your limb bends, or you want to shorten the amount of limb that is bending.
When should you not use them? When you are happy with the design that you have assuming it doesn't use them. I know I was never really interested in using them until I discovered this site. I didn't see any advantage, boy was I wrong! They made a huge difference in the way my bow shoots.
How thick and how long? I guess that would depend on your design and what you want them to do. As I said early I have little experience. My p/l is 11" long and about 1/16". I have been using a seven inch tip wedge that tapers from 1/16 to zero.
How much is too much? I don't know, some of that would again depend on design and draw length. I assume if you go to far your limb will in effect be too short and overly stressed. Would have a negative effect on how smooth it would draw etc.

[badger5149]

I think the tip wedges and power wedges also let a custom bowyer design a bow very much for what it was intended. If an archer shot a 45# bow and indicated he wanted to shoot very heavy arrows like 15 grains per pound you could shorten the power wedge for instance. I think the primary function of the power wedge is increeasing efficiency in a bow by reducing vibration. The heavier arrow one shoots the less need for this and conversely if the bow is intended as a target bow shooting maybe 7 grains per pound you could extend the power wedge out further to accomadate this at a slight loss of stored energy but more than make that up in effiency. The tip wedge as said earlier simply helps to maintain string angles and can also be used in customizing a bow according to the job it will be doing. To see very dramatic results shooting very light arrows around 4 or 5 grains per pound will help demonstrate this. Steve

[jwillis]

1) What is a Power Lam?

A power lam is a short, forward tapered lamination located at each end of the riser.

2) What is a tip Wedge?

A tip wedge is a short, reverse tapered lamination located at each of the limb tips.

3) What do they do (simple answer)?

Power lams effectively lengthen the riser by extending the length of the fade-outs. This thickens and stiffens the limb near the fade-outs and pushes the working area of the limb out farther towards the mid-limb or mid-outer-limb. This reduces moving mass which speeds up the limb as it recovers during the power stroke. Tip wedges gradually thicken towards the tips, keeping the outer four-to-six inches of the limbs stiffer during the draw. Stiffening the tips reduces the limb angle during the draw, allowing the bow to stress the working area more and store more energy. It also reduces stacking , which enhances the sweet spot of the draw and extends the draw length.

[Kirkll]

good stuff here guys, and its already been pointed out what these wedges can do.... i think badgers analogy of the use of them is excellent. i does allow the custom bowyer the option of taking one form and making many different kinds of limbs for each intended purpose and draw length.

now i'll chip in a few thoughts about how to use them. every design has a little different geometry which bends differently depending on taper rate of your lams, and the weight being drawn, and the amount of R/D. The tip wedge thickness , and stiffness of the power lam you use changes depending on what the weight and draw length. for example i'll use an .040 TW on a 50 pound bow. and only a .030 on a 40 pound bow. if i have a 65# i'll go up to .050 on the same length limb. the lighter poundage bows i shorten the length in proportion from 4 to 5" down past the TN.

with a power lams, i've experimented with different taper rates, and different lengths extending past the fade tips and even TD wedges that i call a "cant", which is short for cantilever. this extra length of the fade tip does more than just push the working limb out further too. like Steve mentioned it has a shock absorber effect that relieves the stress point on the fades, and i believe stores energy that is recovered rather than going into the riser in the form of shock.
i vary my taper rate on my PW's from .013 to .009 depending on what i'm trying to accomplish, and slip the cant past the fades from 2-4" depending on the material used for the PW itself.

Are these wedges necessary to build a good shooting bow? Absolutely not.....if you had the right machinery and sleds set up to grind multi tapered lams, once you have the design dialed in you could eliminate the wedges completely, and alter the stiffness in direct proportion to the poundage with different materials and thickness of your stack..... theoretically .... i say theoretically because i haven't played with multi taper sleds, but i know some bowyers who do production bows this way that swear by it.

there's my .02 cents

[Sixby]

Excellent information. Jim you basically nailed it down so anyone could understand. Good stuff from Steve and Kirk. Nothing to add here except agreement. I certainly agree with Kirk about the shock absorber effect. I have not lost a single carbon limb since I started using power wedges. they are the best insurance against carbon blowup you could have if you remember that carbon hates curves and does not compress.

[jwillis]

I like what Kirk said about Badger's analogy, which also brings something else to mind... Power lams and tip wedges are a good way for a composite bowyer to adjust the thickness of the limb in specific areas like a wood bow maker does when he scrapes the belly of the limbs to make them bend evenly and to reach the intended draw weight. The real challenge and disadvantage of using them in a composite bow is you can't adjust them once they are built into the bow. To make an adjustment, you have to take notes and change their thickness, length, etc., on the next bow. Still, I see them as a necessary tool for dialing in the limb thickness because the thickness of the limb determines the most how the limb will bend. Jim