Laminated bow limb timing?

[Swissbow]

You don't need any high tech gadgets to check if you got a nice shooting bow or not. First thing after sanding the limbs is checking the tiller. I do this by measuring the distance from both ends of the riser onto the string.

 

Since I want a slightly positive tiller, the distance at the lower end of the riser should by a little less than at the upper end of the riser ( approx. 1/4" ).

If the draw weight is still to high I reduce it at about 2-3lbs above the target weight. While doing this I always check if the tiller is still correct. Then I shoot a few arrows that are rather on the light weighted side, because heavy arrows will absorb some of the eventually remaining vibrations. If limb timing is not correct or the limb masses are not equal the bow will show by more or less vibration while shooting. Now comes the hardest part, that is to find out where and how much to sand off. I usually start by giving one limb 10 strokes with 180 sanding paper on each side of the outer third of the limb. Then I check again if it got better or worse. If the vibrations decrease I know that I'm on the right track. If not I know I have to work the other limb. I go slowly and always check if it's getting better. At the same time it's also important not to forget the tiller. It may sound complicated, but in fact it is not that difficult. You just have to try and with some bows under the belt you'll gain more experience how it works.

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Andy

[Brock]

okay i think we all get the tiller...timing is the topic.

so you cause the limbs to vibrate and sand until it stops decreasing, hoping to not go too far...and while also trying to not affect the tiller?

so if timing is not having both limbs traveling at same rate and in synchronized movement...is it really timing?

From descriptions it sounds like we have tiller...which we know is a mainstay of bow building.  Then we have something that is really HARMONICS.....not timing it appears from latest description of how to identify and deal with it.

[longrifle]

I'm still getting confused.So is perfectly tillered bow,a perfectly timed bow as well?

[LC]

I guess I'm just lucky but if I get the tiller right I'm usually dead nuts on with a great shooting bow! If not I'd sand till it was right. BUT I've never ran into that. YET! Based on the poundage I bareshaft shoot some arrows! I've never been lucky before is what is weird, if I was gona be lucky I wish it was on the winning the lottery!

[Bowjunkie]

Brock, syncronized limbs return to brace at precisely the same instant, but aren't necessarily sync'd in movement or appearance througbout the draw.

Suppose unbraced one limb has deflex and the other has reflex... this bow can be tillered to bring the nock of the arrow straight back without wanting to tip in the hand, but the limbs won't be mirrored images of one another... and won't look as if prescribed to a tiller measurement 'standard' at brace. So too with a bow that has one limb longer than the other. Its limbs travel different distances, one in a tighter radius than the other, but need to return to brace in sync. The Japanese Yumi bows take this to an extreme, but the same applies to bows with much less difference between limbs.

I'm afraid many folks believe tillering to mean only 'to cause the limbs to bend in nice even arcs'... and nothing more. Maybe they'll also cause all of their bows to show 1/4 or 1/8" positive tiller, and then assume they're well-tillered/sync'd, but I've found that's not always the case. It's my opinion that limbs should be 'tillered' to bring the nock of the arrow straight back and send it straight forward. The only way that's going to happen is with limbs that apply equal tension to the string... relative to our grips on handle and string... and when that is our destination, and our compass that steers our efforts, the result is a perfectly tillered bow, regardless of what its brace height measurement are... and vary they will. Those measurements aren't completely useless however. They can be taken after the bow is tillered, and before shot-in. Then used as reference during shooting in and early life to reveal any tiller shift that might occur. As I mentioned before, those measurements should be the final product of our efforts, not a factor that at all steers them. I don't take those measurements until the bow is completely tillered and ready to be shot at full draw... and then I take the tape measure to the bales with me to make occasional checks to ensure the tiller isn't changing as she's shot in... which as a general rule, it never does.

Longrifle, yes, a perfectly tillered bow is, among other things,  perfectly 'timed'.

[Swissbow]

I take these measurements as a starting point and in general I'm already pretty close. Timing of the limbs has a lot to do with the mass of the limbs. The heavier they are, the slower they move forward and the more energy is used to do so. The tiller of a bow may look perfect, but if the mass of the limbs is not properly balanced, you'll still get vibrations, because the limbs don't work in synchrony.

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Andy

[dfrois]

Okay, this is interesting, but how do you balance limbs that are imbalanced, if not by tillering? Or, to put it another way, what can you do to the limbs, to rectify balance, that does not afect the tiller of the bow?

The only thing I can think of is to add weights, in the right place, to the faster limb (the one that gets to brace sooner). A bit like balancing car wheels...Of course, finding out how much weight, and where to put it, would be very difficult, I think...or is there something else?

DF