[The Phantom]

Bare shaft tuning indicates weak spine.
2008 Martin Bengal 29" DL / 52# DW
Beman Bowhunter 400 arrows 29" w/ 100gr tips.
Charts say this is the correct spine, but I can't get bare shafts close to fletched arrows. No matter how far I move the rest the bare shafts are far right.
I put a 75gr and a 125gr tip on the bare shafts and the 125 was slightly better. Any suggestions on an arrow?
Thanks

 

[psargeant]

Are you left or right handed?

Bare shaft right would indicate a weak spine for a right hander, (stiff for a lefty) but if the 125 grain point is showing better than the 75 grain point, that indicates a Stiff arrow.

Have you tried turning the bow up (or down) and seeing what that gets you?

If the 125 grain points are better, try using them and turning the bow up even more and see what you get...

You should also check for idler lean and make sure you don't have any clearance issues through your rest...

You could also chop 1" of carbon off your arrow if you are in fact weak. You should have plenty left and that will help to stiffen up the arrow's reaction...

 

[The Phantom]

Answers

Answers in blue.
Tahnks

Are you left or right handed?
Right handed.

Bare shaft right would indicate a weak spine for a right hander, (stiff for a lefty) but if the 125 grain point is showing better than the 75 grain point, that indicates a Stiff arrow.
I know, that threw me for a loop, not the results I expected.

Have you tried turning the bow up (or down) and seeing what that gets you?
No, I was hoping changing the weight would help me solve the problem since I shoot 100gr.

If the 125 grain points are better, try using them and turning the bow up even more and see what you get...

You should also check for idler lean and make sure you don't have any clearance issues through your rest...
Not sure how to check idler lean.
No rest contact. Sprayed foot powder on the four fletched arrows and shot them several times. No contact anywhere.

You could also chop 1" of carbon off your arrow if you are in fact weak. You should have plenty left and that will help to stiffen up the arrow's reaction...

 

[psargeant]

Idler lean...

Lay an arrow shaft against the idler and run it towards the center of the bow. If the idler is straight, the arrow will parallel the string, if its not, the arrow will either cross the string or move away from it. Add/remove twists to the split yoke to get the arrow to run parallel to the string...I am assuming this is the single cam one in your profile pictures...???

You've tried turning the bow up and down, moving the rest, with no change to bare shaft reaction? That just doesn't make sense...maybe the idler lean thing will play out...

Short of those things, I would guess its more of a form issue or something truly off the wall like a bent riser or twisted limb or something...

 

[The Phantom]

Thanks

again.

Idler lean...

Lay an arrow shaft against the idler and run it towards the center of the bow. If the idler is straight, the arrow will parallel the string, if its not, the arrow will either cross the string or move away from it. Add/remove twists to the split yoke to get the arrow to run parallel to the string...I am assuming this is the single cam one in your profile pictures...???
Yes, single cam Martin. So I lay the arrow against the idler and let it run towards the cam? Then based on position of arrow vs string I adjust the yoke? Sounds easy enough.

You've tried turning the bow up and down, moving the rest, with no change to bare shaft reaction? That just doesn't make sense...maybe the idler lean thing will play out...
Haven't adjusted DW, that's why I tried different weight tips. Thought it would do basically the same thing, make the arrow stiffer or weaker. Moving the rest helped to a point, now the fletched and bare shafts move about the same. I put a new cable and string on this weekend so it's possible I need to adjust for idler lean as you suggested.

Short of those things, I would guess its more of a form issue or something truly off the wall like a bent riser or twisted limb or something...

 

[tuneman]

i've yet to get rid of the same tail left in my moab, its 29" with 55lb draw and using 400 spine carbontechs and i've tryed everything and its still there so i just live with it

 

[psargeant]

again.

You need to work the draw weight to see what changes that makes. point weight already seems to make a difference indicating a possible spine issue. Knowing that working your draw weight until you find what happens can help you figure out what you've got, or may solve your problem altogether...

You likely do have some issues with idler lean if you haven't accounted for it after installing new strings...

 

[The Phantom]

Ok.

Working three 12s this weekend so probably won't get to it until Mon or Tues. Will check idler lean first, then adjust DW. Don't have a scale so will just take it about two turns each way and see how it works.

You need to work the draw weight to see what changes that makes. point weight already seems to make a difference indicating a possible spine issue. Knowing that working your draw weight until you find what happens can help you figure out what you've got, or may solve your problem altogether...

You likely do have some issues with idler lean if you haven't accounted for it after installing new strings...

 

[psargeant]

Working three 12s this weekend so probably won't get to it until Mon or Tues. Will check idler lean first, then adjust DW. Don't have a scale so will just take it about two turns each way and see how it works.

Take it a couple tunrs up and see what happens, if the point weight isn't lying to you, bare shaft should return to the middle...if turning it down makes it better, you know your arrow is weak. Cut another inch off and see what happens...

Let us know ok?

 

[The Phantom]

Idler lean

Didn't have to wait until Mon. Adjusted idler lean and still couldn't get bare shaft to hit close to fletched arrows. Took two or three turns off the limbs and this is what it looks like. This leaves me to believe I need a stiffer arrow, correct? Would a 340 be too stiff? Is there something between a 340 and a 400?
Thanks.

 

[The Phantom]

Ttt

so those helping will see the results.

Take it a couple tunrs up and see what happens, if the point weight isn't lying to you, bare shaft should return to the middle...if turning it down makes it better, you know your arrow is weak. Cut another inch off and see what happens...

Let us know ok?

 

[psargeant]

If you're not stuck on an all carbon arrow, you can find arrows between .400 and .340...

I still say you need to just lop 1" off the end of the arrows you have. They're much longer than they need to be, cutting off the extra inch should get you darn close...I'd at least try it before I spent the money on new arrows...

 

[jca]

I agree...Chop 1 in. off and the spine should be right on! You're only going to loose 9-10 grains.

 

[The Phantom]

So

to be safe I need to strip three arrows, have them and my unfletched arrow cut down an inch, refletch three, shoot a group and then the unfletched and see where I am?

Or just have the unfletched cut down, shoot it and see where it is in relation to the group from earlier?

Thanks

If you're not stuck on an all carbon arrow, you can find arrows between .400 and .340...

I still say you need to just lop 1" off the end of the arrows you have. They're much longer than they need to be, cutting off the extra inch should get you darn close...I'd at least try it before I spent the money on new arrows...

 

[birdman]

Sounds like you need to shorten the arrows..do you have your rest slid back from the riser as far as you can...that will let you shoot a shorter arrow too..if your a 29" draw length then you shouldn't have a arrow longer than 28"....JMO

 

[psargeant]

to be safe I need to strip three arrows, have them and my unfletched arrow cut down an inch, refletch three, shoot a group and then the unfletched and see where I am?

Or just have the unfletched cut down, shoot it and see where it is in relation to the group from earlier?

Thanks

I would pull the points, chop 1" of the point end, re-install the inserts and go from there. Much easier than refletching...If you used epoxy, you'll probably just have to cut the shafts and install new inserts...

You can probably get a good idea if it's going to help by just cutting your bare shaft, but to really know you're going to need to cut 3-4 of the fletched arrows too. It isn't like the arrows are doing you any good now anyways...

 

[The Phantom]

I like

to keep the broadhead at the front of the riser, that's why I shoot a 29" arrow. I could take almost 1 1/2" off and still have a little clearance from the rest.

Sounds like you need to shorten the arrows..do you have your rest slid back from the riser as far as you can...that will let you shoot a shorter arrow too..if your a 29" draw length then you shouldn't have a arrow longer than 28"....JMO

 

[The Phantom]

Thanks

I thought of that later and that's what I did. Had four cut down to 28". Now to wait for the rain to leave so I can try it again.

I would pull the points, chop 1" of the point end, re-install the inserts and go from there. Much easier than refletching...If you used epoxy, you'll probably just have to cut the shafts and install new inserts...

You can probably get a good idea if it's going to help by just cutting your bare shaft, but to really know you're going to need to cut 3-4 of the fletched arrows too. It isn't like the arrows are doing you any good now anyways...

 

[psargeant]

I thought of that later and that's what I did. Had four cut down to 28". Now to wait for the rain to leave so I can try it again.

let us know how the testing goes...