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Phoenix, AZ
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Can anyone tell me what type of behavior would you expect in regards to adjustment of your cushion plunger:

- Plunger too far out (ex. arrow fully outside of center-shot)?

- Plunger too far in (ex. arrow fully inside center-shot)?


What I'm looking for is the expected behavior you would expect to see when trying to bare shaft tune under these conditions.
 

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Plunger out too far - If the arrow spine is well matched to your limb weight and draw length (holding weight), then Plunger too far out will make the bare shafts act too stiff and you'll get 'nock right' at impact. If you have to have the plunger button way outside of centershot to get the bare shafts to impact at the same angle of entry as the fletched arrows, then that indicates to me an arrow spine that is too weak for your holding weight, and you're trying to compensate for that weak arrow by running it outside centershot to make it act stiffer.

Plunger in too close - the reverse of above .... If arrow spine is well matched to holding weight, then plunger inside centershot will result in 'nock left' at impact. If you have to have the plunger button way in of centershot to get the bare shafts to impact at the same angle of entry as the fletched arrows, then that indicates to me an arrow spine that is too stiff for your holding weight, and you're trying compensate for that stiff arrow by running it inside centershot to make it act weaker.

The problem with both scenarios is that arrow is not then seeking the target in a straight line, but in a horizontal arc, so changing distances will necessitate changes in your 'windage' on your bow sight to try and 'time the arc intersection with the new distance'. Like the difference between a straight fastball and a curveball - move the plate back 3 feet and the fastball is still over the plate, whereas the curveball at the new distance will require a new vector from the mound in order to intersect/be over the plate.

(I hope I got this right).
 

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As above. However I don't think adjusting center shot is a good idea for basic (bare shaft) tuning. More sensible to set and forget and use the button spring for tuning adjustment. Have heard that center shot adjustment is suggested as an ultra-fine tuning method to adjust arrow shaft bow exit alignment but this is way above my pay grade so no opinion.
 

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As above. However I don't think adjusting center shot is a good idea for basic (bare shaft) tuning. More sensible to set and forget and use the button spring for tuning adjustment. Have heard that center shot adjustment is suggested as an ultra-fine tuning method to adjust arrow shaft bow exit alignment but this is way above my pay grade so no opinion.
It seems to me that center shot can be adjusted using the spring or the plunger position and I'm a bit confused as to which to use. I discovered your (Joe T's) suggestion that plunger tension should be in the range of 300 to 500 gram-weight equivalent force, which is a bit higher than I've usually used. What if I find that plunger tension is much lower than this range with the correct center shot. Does that mean that my arrows are too stiff?
 

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Can anyone tell me what type of behavior would you expect in regards to adjustment of your cushion plunger:

- Plunger too far out (ex. arrow fully outside of center-shot)?

- Plunger too far in (ex. arrow fully inside center-shot)?


What I'm looking for is the expected behavior you would expect to see when trying to bare shaft tune under these conditions.
Rick McKinney’s book has a good write-up on this problem. First, you have to distinguish between fishtailing and planing. Planing can mask fishtailing, which in my personal experience can cause a tuning death spiral.

If the center shot is significantly off, a bareshaft nock will kick left (too far in) or right (too far out) upon release and will seem to hang there momentarily and then begin a wide, sweeping back and forth motion. This is very different from fishtailing which is much more rapid. Once you have experienced both the difference is unmistakable. The amount and speed of either of these can vary of course, and everyone will have an exception to the rule, but this has been my experience.

The remarkable thing about planing is that your arrow can be a perfect match or set up for the wrong spine and you won’t know it because planing dominates. If the arrow is correct and your bare shaft planes, adjusting center shot to eliminate it will have immediate, pleasing results. You may still have to do some tuning, but your arrows will be flying straight and all is good.

If the arrow spine is incorrect, eliminating a center shot/planing problem should result in fishtailing. This was a eureka! moment for me years ago when no matter what I did I could not get the expected results from adjusting…everything else. I thought planing was the same as fishtailing and I couldn’t get rid of it. Read "The Simple Art..." , got the correct center shot and the arrow suddenly fishtailed on the very next arrow (eureka!) and then, and only then, did I start to get the expected results from adjusting limb weight and plunger tension.

Distinguishing between planing and fishtailing is best done at longer distances, so this problem may be harder to address if you are only tuning at 18m.

(The preceding is another reason why “The Simple Art of Winning” should be a part of every archer’s library, imho). :)
 

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It seems to me that center shot can be adjusted using the spring or the plunger position and I'm a bit confused as to which to use. I discovered your (Joe T's) suggestion that plunger tension should be in the range of 300 to 500 gram-weight equivalent force, which is a bit higher than I've usually used. What if I find that plunger tension is much lower than this range with the correct center shot. Does that mean that my arrows are too stiff?
Although playing about with button tension and center shot have a similar effect on relative hit positions of fletched shaft and bare shaft they are not the same in terms of the cause. Button spring tension is about the lateral force on the arrow from the riser contact whereas center shot is about the lateral force on the arrow from the bow string. Center shot also ties into the archer arrow release and the arrow alignment so I prefer to stick to the simpler button tension as regards basic tuning - archer's choice as ever :).

The 200-300 gram suggestion was only for initial bow set up i.e. having a button that would not effect the draw weight adjustment for the bow set up (a button spring that's too stiff or too soft will end up giving you the wrong draw weight for matching the arrow to the bow). Actual spring button tension resulting from tuning depends on the draw weight - the higher the draw weight the higher the required button spring tension. Don't know but guessing the actual range across everybody might be 150 - 600 grams. Having a lower spring tension (i.e. a sensible center shot) where the spring has "less to do" seems to me a good idea. This is why I prefer to "fix" and leave center shot in the standard position - it results in an acceptable spring tension.

The minimum spring tension is the one where the button is not depressed by the action of the clicker on the shaft. If you bend your clicker blade against a grain scale it gives you a number for the minimum spring setting - something less than 100 gram typically. Not an issue unless you have a very low draw weight.
 

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Although playing about with button tension and center shot have a similar effect on relative hit positions of fletched shaft and bare shaft they are not the same in terms of the cause. Button spring tension is about the lateral force on the arrow from the riser contact whereas center shot is about the lateral force on the arrow from the bow string. Center shot also ties into the archer arrow release and the arrow alignment so I prefer to stick to the simpler button tension as regards basic tuning - archer's choice as ever :).

The 200-300 gram suggestion was only for initial bow set up i.e. having a button that would not effect the draw weight adjustment for the bow set up (a button spring that's too stiff or too soft will end up giving you the wrong draw weight for matching the arrow to the bow). Actual spring button tension resulting from tuning depends on the draw weight - the higher the draw weight the higher the required button spring tension. Don't know but guessing the actual range across everybody might be 150 - 600 grams. Having a lower spring tension (i.e. a sensible center shot) where the spring has "less to do" seems to me a good idea. This is why I prefer to "fix" and leave center shot in the standard position - it results in an acceptable spring tension.

The minimum spring tension is the one where the button is not depressed by the action of the clicker on the shaft. If you bend your clicker blade against a grain scale it gives you a number for the minimum spring setting - something less than 100 gram typically. Not an issue unless you have a very low draw weight.
Thanks for the excellent and thoughtful explanation.
 

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Genesis 21:20
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Centershot adjustment is critical. But I'll also add that there is a very good reason we have adjustable limb bolts on our risers too... ;)
 
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