Limb timing problems

[mikkekeswick]

So I read the thread on timing the limbs via a moveable lower pulley and a straight line in the correct place with regards to finger placement on the string. It makes sense and I would like to get the method dialed!
However i'm having problems with the shape of the bow handle cradle. Should I make the cradle fit the pistol grip of my riser exactly? I have done this and when I place the bow on it sits nicely. When I pull on the rope the upper limb immediately tips down (due to the physical weight of the bow) but if I continue to pull on the rope the hook drifts back to the line and then parallels it to full draw.
I'll try and take some pictures to show what I mean better!

[mikkekeswick]

Also my bow making past has always been with wood only bows/horn bows and I have never had a problem making a bow that is 'dead in the hand' upon shooting....a few months ago I started making glass bows and just can't seem to get the same feeling? They always seem to have a bit of 'buzz' to them? Is it possible to make glass bows totally free of any handshock? Or am I chasing an impossible goal? I've never shot anybody else's glass bows so I don't really have a reference!

[Roy from Pa]

Mike it sounds like it's ok if the hook comes back and tows the line. Remember, we are pulling more towards the top limb as we pull the trees pull rope so that applies more pressure to the top limb. And if the top limb is a little longer than the bottom limb it compounds the pressure applied also. But the bottom line in limb timing is having the pull rope tow the line as it comes down the tree. I leave my grip area alone till after the bow is done being tillered. Look at the picture I attached and you can see how my riser and cradle are matched evenly. The bow sits in the cradle perfectly flat. When I first put a bow in the cradle, I will adjust the riser by removing a little wood off one side or the other depending which end of the bow is higher, till I have the bow laying perfectly level. That doesn't require very much wood removal.. Look closely at the cradle ends and you can see how it's cut at a slight angle and the riser is cut to the same angle.

     

 

[Bowjunkie]

Mike, you said when you pull the string, the top limb tilts down... If it does so sharply, that sounds like what happens when a symmetrically made bow is 'properly' drawn on a tree because the string is pulled far above center(its static balance point). Ultimately, if we balance the limbs well enough, it will drift closer to the line the farther it's drawn and somewhere prior to full draw, it should be right on the line... i.e. dynamically balanced at full draw... if we do our part balancing the limbs by wood removal.

What you are seeing is the beginning of 'the shift' between static and dynamic balances that happens when many bows are drawn. Even asymmetrical bows will do it to a lesser degree if the longitudinal center and string fulcrums are separated.(as mine often are). I find this shift, if bad enough, can negatively affect how a bow feels during the draw and release, and even think it affects arrow flight and tuning ease/difficulty. Its severity depends on location of longitudinal center relative to string hand fulcrum, and can be greatly reduced, even virtually eliminated by designing these factors in close proximity to one another, or even at the exact same spot in some instances.... and these, if the limbs are in fact balanced relative to the archer's holds, make the most predictable, inherently tuned, sweetest drawing and shooting bows, imho.

Does your bow have same length limbs, or a shorter bottom? Do you shoot split finger, three under, or?

[fujimo]

wha....??!!?
gotta read that again- slower this time   :D

[Bowjunkie]

I'll add... the farther the string hand fulcrum is above the bow's center, the greater the shift, AND the more difficult it will be to navigate to dynamic balance at full draw.

The converse is true as well.

...the closer they are, the easier it is, and the sooner in the tillering process balance can be sought.

[Bowjunkie]

Oh... hi Wayne    

[Bowjunkie]

A couple of for instances....

A symmetrically designed bow, shot split finger puts the string fulcrum almost 2" above bow center. BIG shift.

While an asymmetrical bow, shot three under can put the string fulcrum and bow center in the exact same spot. NO shift.

Even if both bows are tillered so they're balanced at full draw relative to the archers, the second bow will feel and shoot better.

[Bowjunkie]

I'll add... the farther the string hand fulcrum is above the bow's center, the greater the shift, AND the more difficult it will be to navigate to dynamic balance at full draw.

The converse is true as well.

...the closer they are, the easier it is, and the sooner in the tillering process balance can be sought.

[Roy from Pa]

I suppose you could be correct a little bit there, Bowjunkie..  
I've put bows on the tree and have had to work on them to progress through the shift, and I've put bows on the tree and they were balanced right from the very first pull of the tree rope. Those latter bows were more balanced because I learned about the shift and the more pressure applied to the top limb through experience after tillering so many bows for equal limb timing. So to help with the shift and limb balance from the start of tillering, I began over building the top limb thickness by about 1/16th of an inch. It has helped immensely. And it results in a more even brace height look. Before doing this, a bow that's timed would look odd to me, having such a negative tiller at brace. Even though at full draw the tiller looked even and perfect, which is more important than how it looks at brace. And since tillering for equal limb timing, it amazes me how smooth, quiet, and accurate my bows shoot.
Right Wayne?  

And that IS exactly why I shoot three under..  

[LittleBen]

I remember watching a TV show about the physicists Stephen Hawkins and Leonard Suskind debating the nature of black holes and the destruction of information from the universe in them. I get a similar feeling when the talk about tilering along the line starts.

[fujimo]

[mikkekeswick]

Thanks for the replies guys.