lower limb problems

[dragonman]

one problem I have been having repeatedly, with practically every bow I've made. The lower limb always ends up more stressed than the upper, and bends more, putting the tiller out. I've tried making the lower limbs wider, this didn't work,nor when I made it thicker or shorter. Now I've read to make it longer? I believe the problem is caused because the knocking point is above centre on the string??
  I would be very interested to hear how others have solved this problem, it might help me with my next bow. Has any one tried the longer option?

[bcbull]

 dragonman  did you add 1 inch  from center  when you layed out ur handel  on the bow ?   we need to see some pic s brock

[dragonman]

the pics are on the way, my sons a computer wiz, he'll be here in a few days .

can you clarify the 1" from centre??

[Pat B]

The bottom limb always gets more stress. That's why you make it a slight bit heavier so it bends a little less than the upper. I set my bows up symmetrical and try to get the bottom limb bending less...but I am not always successful. The nice thing about a symmetrical bow and a bulbous handle is it the bottom limb over stresses you just flip it over and make it the upper.    Pat

[dragonman]

thats exactly what I've been doing, I just keep turning them over, untill the tiller eventually balances, but my last bow, had an arrow shelf and grip and couldn't be revervsed, so I would like to get on top of the problem.

[artcher1]

Sounds like you're not stressing both limbs evenly as you tiller out your bow. Think in terms of evenly stressing both limbs from the flooring stage to the shooting-in stage. If at any point you overstress one limb over the other then you'll create more set in that limb. I suspect you're overstressing the upper limb while tillering out your bow and then overstressing the lower limb during the shooting-in stage. Overstressing the lower limb is caused by the bow hand pressure created by the upward angle of the drawing hand  (Not here: this will not cause uneven stress on either limb if even stress on both limbs is maintained during the tillering process). 

So, to keep a long story short, it sounds like you're not stressing the lower limb enough during the tillering stage and then overstressing it to much during the shooting stage. 

Are you using a tillering board/tree? ART B

[dragonman]

archer1, I 'm not sure  how I'm overstressing the bows during the tillering or the shooting in process?, I tiller on a tillering tree untill both limbs are equal at brace height then slowly increase the draw, usually by the time I reach full draw this way the tiller is reasonable, then I shoot some arrows after about 50-100 arrows, the bottom limb has  took more set than the top, but I dont understand why the shooting in would over stress the bottom limb more than the top. and why is there more upwards stress on the bottom limb? I'm not saying your wrong I'm just trying to understand!

[Jim Davis]

I've wrestled with this "lower limb is stressed more" for years and couldn't make sense of it.

I think I may have figured it out. IN MY CASE (your mileage may vary) I stress the lower limb more when stringing the bow.

I use the centuries-old push-pull method. When I pull at the handle, my pushing hand is only about 3/4 of the way up the upper limb. That means pretty much all the bend is in the lower limb. I can see it is bent too much when I'm doing it.

So, now I put my pulling hand at the top fade when stringing. It won't bring back any of my overstressed lower limbs, but it may keep from overstressing new ones.

Reparrow man

[artcher1]

Dragonman, I was referring to stressing one limb more then the other, not overstressing your bow. Sorry I didn't make that clear.  There are several reasons why the lower limb gets out of tiller. One is from over heeling the bow or in simpler terms, improper grip per arrow pass layout.  Example: using a low wrist or full hand contact on a bow designed for a straight wrist or low contact grip. Another is unequal moisture content created by standing ones bow upright in a corner for an extended period of time. But I doubt if the latter is your cause.

To give you a better understanding of what I'm talking about as far as that upward angle causing extra stress to the lower limb try this. String one of your bows and as you draw it back apply some heel pressure to the heel of your handle. You will see that it naturally places extra stress on the lower limb.

That's the reason for positive tiller using a slightly stiffer lower limb to compensate for the extra stress.

Are you setting your bows with an even tiller or positive? ART B

[dragonman]

that is very interesting, I hadn't really considered the influence of a full hand or partial grip, on the stresses of the bow! you could be onto something there.
by a posotive tiller, I presume you mean making the lower limb stiffer? I do try to this, but they have still ended up over stressed. then I compensate later by taking more off the upper limb, but this brings the weight down.  Thanks for the imput, theres stuff for me to think about there.

[Gordon]

I tiller my bows so the lower limb is stiffer than the upper limb - that typically manifests itself as a 1/4" positive tiller.

[Eric Krewson]

The lower limb getting weaker over time is a common problem. I make my bow limbs of equal length so if this happened I can pike the lower limb an inch and bring the tiller back in line without loosing any poundage.

[artcher1]

I'm starting to see more benefits to equal limbs (handle dead center) as well Eric. Better for piking as you mentioned. Easier to achieve even limb mass which promotes better limb timing. Better odds of holding tiller profile over time (for the bows I give away). And easier to tiller out (at least for me). 

My upper and lower limbs are predetermined (I build my bows as they stand in the tree) even with same length limbs. But for those that like to build their bows and then swap ends  as needed, this is another benefit.

But a good understanding of the different forces applied (from the hand grip and tillering tree) to the upper and lower limbs  during the tillering and shooting-in phases will help with eliminating lower limb problems.-ART B