Centering the string.

[Prarie Bowyer]

GRRRRR...

At this point I'm 98% certain that the bulk of limb twist issues are grain related.  So I have a R/d bow coming along.  Loks NICE.  Tiller bending looks good.  Got into the home streach and ther is a tad of limb twist.  The limb rotates and the tipp is pulled off center.  Now if it were a shoot off the knuckle I'd just flip the bow over and leave it.  Unfortunately the guy wanted a cut in arrow shelf.  Naturaly the off centered string can't go towards the shelf but the other side.

My plan to fix it has been adjust hte nocks a tad.  Shave wood from the side of the bow in the area opposite the string  focusing at areas across and just above where the limb is pulled off center.  I did this once and seemed to work well. 

This time My bow belly is clearly different thicknesses when viewed from the side.  BUT it's flexing toward the thick side almost as if it's not reduced enough. 

I keep this level tapered piece of maple that has crazy grain to remaind me what is gong on .  I can flex it and feel the twist happening and I can see what needs to be reduced to fix the limb twist.  Then I look at my bow and it gets a bit muddy.

Is this the right approach?  Reduce the fat side of the bow, cut one nock slot deeper to help center up the string and shave the belly in the area just before the twist on the opposite side? 

As I do this I dn't see that much change happening so I loose confidance in my understanding of how to fix it.

[randman]

Whatever side it is twisting or flexing TOWARD is the weak side. It's taken me a while and a few experiments (and a good post on this site) to figure that one out. Do a search on here and you will find that simple example of how the limb twist thing works.

[dwardo]

I have a yew bow that was giving me the same kind of grief. I too experienced the bow leaning towards the thick side rather than thin as you would expect.
For me the problem came from the unbraced view, basicaly the twist was in the recurve unbraced and became more apparent in the draw. I heat treated the bow for a last time last night and whilst heat treating i removed most of the limb twist using C clamps whilst heat treating at the same time.

Seems to have helped.

[Prarie Bowyer]

I'm making a triple laminate.  So I'm cautious to heat treat.  Pluss Ipe is the belly wood and it doesnt respond to heat like that.

[druid]

Twisting do not have to be caused by different thickness. When (for some reason) string moves just a little to one side it causes bow to twist to that side, no matter what thickness is on that side. Then we suspect thickness for twisting but reason could be different. It is more obvious on narrow bows, longbow for example.

[k-hat]

How does the grain run on your limbs?  I had one where the rings ran straight from tip to tip, but it began to propeller twist.  Upon closer inspection, i saw that the radial grain actually ran at an angle that pretty well matched the twist i was seeing when braced and drawn.  Limbs were evenly tapered. 

Just a thought.

[Prarie Bowyer]

K-hat.

That is what I'm talking about.  if Looking at the limb a grain line does not go the full length of the bow.  And if there is run out on the narrow edge it can be an issue also.

Now I test bend each lamination before I glue up.   If one wants to twist one way and the other lam wants to do it also I flip them so they aren't on the same side.  Hopefully a propelering core will be over powered by a straight belly.