Reducing tips and such for speed

[DC]

I'm close to finishing an OS d/r and I thought i could reduce the tips a bit and gain a few FPS. The bow, without string, weighed 625 grams. I took the tips down to about 1/4" wide tapering back up the bow about 6". Tidied up a bit and now it weighs 615 grams. Before the reducing the bow shot 169-170 consistently. After reducing, 169-170 consistently. No change at all. 10 grams is 152 grains, almost one third the weight of an arrow. I was surprised I got no increase in speed. I was using an old string that was 10 strands of FF. It weighed 64 grains. So I made a new 8 strand FF string. It weighed 42 grains. It shot 172 FPS consistently. Speeds are tested on my machine and they are very consistent. Now I understand that the string is a lot closer to the action than the tips so it doesn't take as much weight change to make a difference. But this just seemed to far apart. Roughly half the string weight is at the tips, too. Unfortunately I can't go back and redo the first test.  Does this seem normal to you guys?

[Aaron H]

What does the new string weight?

[DC]

What does the new string weight?

Oops 42 grains, I fixed the OP.

[Badger]

  That's why I quit making my tips ultra skinny. It just doesn't make that much difference. When you accelerate the string you loose all that energy. You get some of the energy back that you used to accelerate the limbs. The forward momentum of the limbs is being resisted by the arrow. I feel as long as they are trimmed up pretty good that's good enough, If you were testing very light arrows you might notice a little more difference.

[bushboy]

You guys are breaking my bias filled heart!lol!

[wizardgoat]

Don a few years back when I first got my Chrony I also did a very similar test on a yew bow. I don’t have any numbers or anything and I didn’t weigh the difference, just narrowed the tips and I was surprised that there wasn’t a noiticable difference. You’d probably see more of a difference going from fairly fat and chunky tip down to very narrow ones. I know your bows have quite narrow tips to begin with!

[Weylin]

I slim my tips because they look nice. I don't think it makes any difference in bow speed. You'd have to have some pretty ridiculously fat tips tip start losing fps. Tiller and design are WAY more important.

[DC]

I'm just surprised that the weight change of the string(20 grains) made a difference and yet 152 grains on the tips made little or no difference. I have to make the assumption that the weight(mass) of every part of the bow that moves will make a difference in the speed of the arrow. The tips are the most massive part that moves the most other than the string. I was sure it would have more effect. I think I will tie some weights to the tips and see if I can back this up a bit. Something I thought might be interesting will be to put unequal weights on the tips and see if the imbalance affects the speed. I'm fairly confident in the machines ability. I get the same number over and over and I have to move the target a bit once in a while because the arrow keeps going in the same hole. I'll use the Chrony because it reads out tenths of a fps, the Caldwell just does fps. Take a few days away from scraping and rasping

[Badger]

  D/C, the virtual mass of a well made bow is only about 150 grains and 1/3 of that is your string. So your talking 100 grains of virtual mass to move the limbs. You get most of that back at the end of the stroke when the leverage changes favoring the arrow. Contrary to popular belief the limbs do not slam home on a well made bow.

[Del the cat]

Gotta remember the centre of the string moves at 3 times the speed of the tips of the bow.
That's why arrow and string weight are more important.
E.G at a 27 " draw the tips of the bow only come back about 9" but the string and tips both return to brace in the same time.
The logic of the experiment is also slightly flawed, reducing the tip mass must to some extent also effect draw weight.
A better test would be to add weights to the tips and see how much is needed to reduce speed by say 5fps. That way every other variable can be left the same.
Even if there is little measurable gain, reducing mass can't do any harm, and several small but barely measurable improvements can make a big difference.
I'm sure we've all re-worked a bow that isn't quite right and made it into a sweeter faster bow with a little work and some fiddling and fettling.

The other side of the coin is the sloppy approach of ... just leave it as it is, it doesn't make any difference. We know that's jut no good.
I often tell people, "It's easy to make bow, it's hard to make a good bow" 
Del

[Eric Garza]

Great thread! Always interesting to me that folks can come up with ideas about how things work, then over time people realize they made a mistake and revert to an earlier way of understanding things. String weight is definitely more important than the weight of tips. I generally make mine 10-15 mm wide where I carve the nocks. That seems to work fine. Not outlandishly heavy, but not outlandishly skinny either.

[DC]

A better test would be to add weights to the tips and see how much is needed to reduce speed by say 5fps.

That's the project for today.

[Badger]

  Tim Baker ran a test many years ago using lead tape on the tips. I don't remember much about the results except it took a lot to make a difference. I still keep mine slim at about 3/8 but the 1/4" tips I reserve only for light arrow flight bows. Lighter arrows do benefit more from lighter tips than hunting weight arrows.

[DC]

The thing that's bugging me is the amount of weight. Like Del said the string nock moves three times as much as the tips so you would expect 30 grains on the tips to have the same effect as 10 grams at the nock point. I wonder if there is some kind of exponential thing going on. Any engineers or physicists on board? I have to finish my coffee and get my hands limbered up and then I'll go play.

[Badger]

  DC, you are ignoring the biggest factor, you don't loose all the energy it takes to accelerate the limbs, most of it goes back into the arrow. I said a few posts up that a well made bow only has about 150 grains of virtual mass and about 50 of that is string mass. Your limbs weigh about 2,000 grains a piece, if it wasn't going back into the arrow your bows would have almost no power at all. 100 grains off your tip is more like 10 grains off of an arrow.