limb vibrations on R/D longbow

reini · October 08, 2019, 03:31:42 AM

Hi guys,
having problems with the latest laminated longbow i built.

I've already built many bows, but this one is the first one showing vibrating limbs.
After shooting an arrow, both limbs are doing strong vibrations for about 3-5 seconds.
It's not a handshock, just these vibrations in both limbs.
Varying the brace height didn't change much.
The tiller i think, is ok too.

Thinking about string material (BCY 8125G), but i'm always using the same and never had this problem on any other bow.

Any ideas out there on how to solve this problem?
Thx Reini

Crooked Stic · October 08, 2019, 07:19:00 AM

Are the limbs bending the same all thru the draw.. In other words limb timing. both ends back to brace at the same time.

reini · October 08, 2019, 07:43:58 AM

Quote from: Crooked Stic on October 08, 2019, 07:19:00 AM
Are the limbs bending the same all thru the draw.. In other words limb timing. both ends back to brace at the same time.

... yes they do, i've checked some positions on the tillerboard.
And there's almost no handshock, so limb timing should be ok.
It's just the strong vibrations on both limbs for a few seconds after the shot.

I can feel and see it vibrating, it's stronger at the end of the limbs, would say the outer halves.
And i think i can exclude the tips, they are really small and lightweight.

Thx Reini

Mad Max · October 08, 2019, 07:53:34 AM

What # bow are you shooting and how heavy are the arrows?

reini · October 08, 2019, 08:03:32 AM

Quote from: Mad Max on October 08, 2019, 07:53:34 AM
What # bow are you shooting and how heavy are the arrows?

draw weight is 40#@30"
bow length 67", R/D glass longbow
Arrows are at 10gpp

Mad Max · October 08, 2019, 08:30:20 AM

I did a search and all I can find is to make a new string with something different.

reini · October 08, 2019, 08:59:53 AM

I'll build a FF+ today and see if it's getting better.
Thx Reini

Flem · October 08, 2019, 10:37:08 AM

Can you post a video of the bow being shot?

Crooked Stic · October 08, 2019, 11:24:15 AM

Yep try a low stretch string first.

Wolftrail · October 09, 2019, 08:03:24 PM

Had a recurve that sung and shook like a stuck goat, changed the string from endless loop FF to a Flemish and also installed furries on the strings. Reduced the noise by 85%.

reini · October 10, 2019, 01:09:17 AM

So, put on a FF+ with silencers and it's MUCH better now.
But it's not gone, still annoying.
Just wondering what the reason is, to avoid it in the future ....

Thx Reini

Crooked Stic · October 10, 2019, 05:13:14 AM

May take about 100 arrows for the string to settle in good if you did not stretch it first.

Mad Max · October 10, 2019, 06:40:55 AM

Move the nock up or down on the string and shoot some

Mad Max · October 11, 2019, 08:45:42 AM

Maybe it needs a little tillering on one limb