Handshock

[Jesse]

I think a sure fire way to find out would be to get 2 bows of similar design and weight one with lots of shock and one without and pull them to the same draw by the same person and film it with a super high speed camera. I think it would be clear what was causing the shock.  Jesse

[George Tsoukalas]

Marc, perhaps we can agree on this. Limb timing as evidenced by a rope and pulley or by shooting the bow and sensing hand pressure on the handle, is another aid to make sure the bow's limbs are in tiller. Tiller off means limbs are not timed. Tiller is not so easy to judge in a character bow. Jawge
http://mysite.verizon.net/georgeandjoni/tillercheck0002.jpg

[Marc St Louis]

George
Perhaps we are thinking of the same thing but using different words to convey our thoughts.

To me if a bow pivots, whether on your rope and pulley or by pulling by hand, it's because one limb is stronger than the other. To me this would make the bow out of tiller. Generally we make bows with 1/8" positive tiller and at that the bow stays steady in the hand when drawn. Increase the positive tiller to 1/4" or even 1/2" and then the bow will pivot. The limbs would still return in unison when shot because both limbs are tied together by the string and when pulled back.

You can move the nocking point up by 2" and the limbs would still come back in unison, they have to because they are tied together and the hand pulls them back in accordance with their requirements. The stronger limb would travel less and be under less strain than the weaker but it would also have more mass, that could increase handshock but still not necessarily so. The weaker limb would be lighter and be under more strain so will come back faster. They both will meet at brace at exactly the same time.

There are external forces that can affect the return, such as if one limbs is much wider than the other and becomes affected by wind resistance.

Tell me I'm wrong

[Kviljo]

The limbs can have a different tiller, and when checked on the tiller, they will always return at the same time. But drawing it and letting it down slowly isn't the same as shooting it with an arrow or dryshooting it. If one limb is faster than the other, it will return faster, and go beyond brace height. When that happens, the string slams tight when one limb has gone past braceheight*, and the other has not reached braceheight* yet. Then the limbs have to return to the normal braced position after the string is tight, giving handshock.

[Jesse]

I am not the expert but Kviljo's explanation makes the most sense to me.    Jesse

[Marc St Louis]

The limbs can have a different tiller, and when checked on the tiller, they will always return at the same time. But drawing it and letting it down slowly isn't the same as shooting it with an arrow or dryshooting it. If one limb is faster than the other, it will return faster, and go beyond brace height. When that happens, the string slams tight when one limb has gone past braceheight*, and the other has not reached braceheight* yet. Then the limbs have to return to the normal braced position after the string is tight, giving handshock.

The one that returns faster will be the limb that is stressed more and that will be the weaker limb but it also has to travel farther because it is bent further. I'm sorry but I still stand by my explanation as the most logical one, until somebody has one that shoots mine down.

[Eric Krewson]

I was tillering a bow yesterday.  It was a new bow that was tillered, shooting sweet and the top limb relaxed a little and the bow got out of tiller. Hand shock went from "0" to toe nail jarring. As I scraped a little of the bottom limb, shooting a couple dozen arrows between scraping the hand shock diminished. When I had the limbs back in time the hand shock was mostly gone. It is limb timing for me that determines most of the hand shock with overbuilt limb mass being second.   

[Badger]

Mark, I tend to agree with yours, I honestly have struggled with this for several years. I can look at a bow now and almost tell for sure if it will have handshock or not but not really sure what I am looking at. I know that makes no sense. I think Eric brings up some good points as well. An overbuilt bow can be deceiving as well. I recently built about 1/2 dozen boo backed osage bows, most of them are near 1 1/2" and slightly less at the fades. The most overbuilt one of them is less than 1" wide near the fades and by far has the lowest mass but because of it's tiller shape it was slightly overbuilt and had the worst handshock. I slightly narrowed the just past mid limb section changing the tiller shape and the handshock was gone. I think most of the handshock takes place because of the near midlimb section of wood not bending according to it's width in relation to the rest of the bow. Steve

[Justin Snyder]

The limbs can have a different tiller, and when checked on the tiller, they will always return at the same time. But drawing it and letting it down slowly isn't the same as shooting it with an arrow or dryshooting it. If one limb is faster than the other, it will return faster, and go beyond brace height. When that happens, the string slams tight when one limb has gone past braceheight*, and the other has not reached braceheight* yet. Then the limbs have to return to the normal braced position after the string is tight, giving handshock.

The one that returns faster will be the limb that is stressed more and that will be the weaker limb but it also has to travel farther because it is bent further. I'm sorry but I still stand by my explanation as the most logical one, until somebody has one that shoots mine down.

My thought goes right along with Steve's mass calculator.  If one limb is wider and thinner it can bend the exact same distance as the other that is narrower but thicker.  The first limb will have more mass and return slower to the original brace even though it is the same poundage of limb.  It is still a 60# limb but is inefficient because it wasn't built to the best dimensions for the wood.  If it is possible to conceive 2 bows that shoot 150 fps and 180 fps with the same length, draw weight and arrow weight, why not conceivable to have two like limbs with some variance? Justin

[George Tsoukalas]

I haven't had time to respond to your post Marc but I will asap. been at church  Gotta go now too. Jawge

[Kviljo]

The limbs can have a different tiller, and when checked on the tiller, they will always return at the same time. But drawing it and letting it down slowly isn't the same as shooting it with an arrow or dryshooting it. If one limb is faster than the other, it will return faster, and go beyond brace height. When that happens, the string slams tight when one limb has gone past braceheight*, and the other has not reached braceheight* yet. Then the limbs have to return to the normal braced position after the string is tight, giving handshock.

The one that returns faster will be the limb that is stressed more and that will be the weaker limb but it also has to travel farther because it is bent further. I'm sorry but I still stand by my explanation as the most logical one, until somebody has one that shoots mine down.

Just to be sure that I understand your argument: you are saying that the limbs of a bow, when shot, will regardless of tiller and mass placement return to the same position as the braced, without one limb going past braced position?

I think that one could be shot down quite easily with a badly made bow filmed by a high speed camera
Shooting it down with words will be a bit more difficult. But I don't think it is correct that the faster limb will be the one that is stressed the most. Imagine an extreme case, where you have a bow with two identical limbs. Both are equally fast, untill you add some dead weight wood to the tip of one the limbs. Now they won't be equally fast, and you could even stress the limb with the dead weight more without making it faster. The one with the dead weight will travel a lot slower, and the string will slam tight before the slow limb has returned to it's (non-motion) braced position.

This could be tested quiite easily, just taping a small weight to the tip of one limb on a bow that has no handshock. It should gain handshock. And the other way around, one should be able to take a bow with handshock, and remove the handshock by adding weights to one limb. - that is, if the handshock was due to timing between the limbs in the first place, and not due to the tiller of the bow.

Interesting discussion!

[artcher1]

What Kviljo said ! That's a why when you lose your positive tiller your arrow's trajectory drops. Here the top limb is stronger and gets home first throwing the path of the arrow downward. Not only do I set my positive tiller while shooting the bow in but I can also adjust my arrow's impact with said tiller. -ART B

[Jesse]

I almost hate to keep weighing in on this but I am trying to learn. It seems to me that when you are drawing back pulling on the string the limbs have to move at the same timing because they are being pulled by the string but when you release all bets are off because now the bow limbs are pulling the string and if they are going different speeds I could see that being a problem. An exact weight on one tip should demonstrate this as was said. I think some experimenting is due   Jesse

[Marc St Louis]

Mark, I tend to agree with yours, I honestly have struggled with this for several years. I can look at a bow now and almost tell for sure if it will have handshock or not but not really sure what I am looking at. I know that makes no sense. I think Eric brings up some good points as well. An overbuilt bow can be deceiving as well. I recently built about 1/2 dozen boo backed osage bows, most of them are near 1 1/2" and slightly less at the fades. The most overbuilt one of them is less than 1" wide near the fades and by far has the lowest mass but because of it's tiller shape it was slightly overbuilt and had the worst handshock. I slightly narrowed the just past mid limb section changing the tiller shape and the handshock was gone. I think most of the handshock takes place because of the near midlimb section of wood not bending according to it's width in relation to the rest of the bow. Steve

Exactly what I mean Steve. By changing the tiller to have the wood work more mid limb you reduced handshock.

[Marc St Louis]

I think that one could be shot down quite easily with a badly made bow filmed by a high speed camera
Shooting it down with words will be a bit more difficult. But I don't think it is correct that the faster limb will be the one that is stressed the most. Imagine an extreme case, where you have a bow with two identical limbs. Both are equally fast, untill you add some dead weight wood to the tip of one the limbs. Now they won't be equally fast, and you could even stress the limb with the dead weight more without making it faster. The one with the dead weight will travel a lot slower, and the string will slam tight before the slow limb has returned to it's (non-motion) braced position.

This could be tested quiite easily, just taping a small weight to the tip of one limb on a bow that has no handshock. It should gain handshock. And the other way around, one should be able to take a bow with handshock, and remove the handshock by adding weights to one limb. - that is, if the handshock was due to timing between the limbs in the first place, and not due to the tiller of the bow.

Interesting discussion!

You are assuming here that a high speed camera would shoot my argument down. An assumption and facts are 2 different things

Adding weight to the tips would slow the limb down but what does that have to do with this? All you are describing here is one limb that has too much mass and another that is well built. I do see your point though. You would have to have a bow that looks extremely odd to have the statistics that you are talking about but you never know. There may be bowyers out there that are unable to see the difference.

By your arguments a bow with unequal length limbs would have tremendous handshock.