Correcting Limb Twist

[Slackbunny]

How do you do it? I tried to search the subject but couldn't find a good thread about it.

I have made a couple successful longbows but everytime I try my hand at a shorter flatbow, I end up getting some serious limb twist. Then in the process of trying to correct it I usually have to remove more material than I want, and end up coming in way underweight, or snapping the bow. I've tried a few different things with mostly poor results.

So how do you guys deal with limb twist?

[gstoneberg]

If the stave itself is twisted, a little limb twist isn't a big deal unless it bothers you or the string slips off the nocks.  It's more important to get the string through the handle.  For serious twist I take the bow to not quite floor tiller stage and then use a heat gun to heat the belly and gently take the twist out adding rocks to a bucket while I'm heating the limb.  Most people build a form or caul, heat the bow, and then clamp it flat to the form.  Either way you're doing the same thing.



George

[Gordon]

If you are consistently experiencing limb twist problems, then most likely it is a result of how you tiller.  Specifically you are favoring one edge of the limb over the other when removing wood. It's really easy to do if you are not aware of it and the wider the limb the more pronounced the effect. When I tiller I am periodically comparing edge thickness on both sides of a limb to make sure they are even.

[4est Trekker]

Assuming it's the result of tillering, here's a link that may help:

http://www.primitivearcher.com/smf/index.php/topic,27206.msg364029.html#msg364029

[Pat B]

I agree with Gordon. If the twist develops during tillering one side of the limb is slightly thicker than the other. Feel the thickness across the limb between your thumb and fingers and you will feel the difference.

[George Tsoukalas]

If the twist was present in the stave and less than 30 degrees I leave it. If I caused it by uneven wood removal I fix it by wood removal. It twists toward the weak side which is the side closest to the string if the bow is strung. Remove wood in small increments from the other or high side. Exercise the stave at very short pulls for changes to register. Continue. Jawge

[Slackbunny]

I will have to keep a better eye on my tillering to make sure I am removing material evenly, I have a feeling that this is the problem. And I never thought of heat treating for limb twist.

Thanks for the help guys. I will keep these in mind.

[George Tsoukalas]

I remember the last yew bow I made years ago. Yew doesn't grow on tress in NH so I was very careful about removing wood equally from both sides of each of the limb...to the point where I checked each side  with calipers. I strung it for the first time. I had a twisted bow that leaned to one side despite even wood removal. So I had to fix it by removing wood from the other sides. You never know. Wood has a mind of its own speaking anthropomorphically. Jawge

[Alpinbogen]

I don't worry about a little twist, but prefer my bows to be pretty straight.  I use an arrangement very similar to gstonebergs picture.  Also as mentioned, it's worthy to take note of your left-right wood removal.  Especially if you're making a wide, flat limbed bow, it could be a tillering issue.

[Prarie Bowyer]

YOu think the heat method would work on a laminated bow with URAC as glue?

[Pat B]

I have heard of folks using light heat to correct twisted lambows, especially if you used Urac.

[crooketarrow]

  You'd have to really be off on your tillering t0 have a limb stwist. I straighten up light swists tillering the bow. Or like GEORGE said it it's less than 30% for get it. It dos'nt look good but no ill affect.
  If your talking about takeing the swist out of your stave before you build your bow. If so I cut it down to bow form and clamp it down heat swisted part and use a pipe wrench to unstwist. Let it cool while your holding out the swist. If it's not straight enough do it again.
 

[Prarie Bowyer]

My twist is coming from the drawing.  Unflexed it's straight.  I looked closer at some shavings from the wood it came from and thoe bend strangely also.  I'm 90% certain it's a grain thing.  Direct Side tillering and agressive belly removal in the high areas removed most of the problem.

I think I finaly understand what is going on here.

[Pat B]

I use my fingers to feel for thickness differences. Your fingers are more sensative to this than your eyes can see. Lightly hold the limb between your thumb and fingers and move down the limb. You will feel the thickness difference as you go. Now go from one side to the other along the limb. If there is a difference in thickness from one side to the other, you will feel it.
  You can also use a tillering Gizmo to check for limb twist. Run the gizmo down both sides of the belly of the drawn limb. It will mark the stiff spots that you need to scrape to remove or reduce twist.

[Prarie Bowyer]

Is there a pic of this tillering gizmo?