Okay, here’s a ‘scoop’, Part of the next Update will have a section on how I apply bare shaft tuning. Since that portion of the Update is pretty much finished I’ll post it here.
A well tuned Extreme FOC arrow requires that the dynamic spine be tuned to the specific bow AND SHOOTER; i.e. it’s something that only you can develop yourself; if you want to get good results. What this means is that you have to bare shaft tune the shaft’s dynamic spine to get the precise degree of actual deflection at launch that gives perfect paradox recovery. Only you can do that because it depends on more than just the bow used. How you hold the bow and how you shoot makes a difference. The pattern of your hand pressure on the bow is important. The quality of your release affects it; and so do things such as your follow-through after the shot.
Bare shaft tuning Extreme FOC arrows is actually a very easy process. Many folks make it more difficult than it is, simply because they don’t seem to understand what they are trying to do, and they often try to mix different tuning methods. That adds layers of confusion in their mind; muddling the decision making process and leading to mistakes in tuning adjustments.
First, understand what you can expect from a weak and strong dynamic spine. If you are right handed, a shaft with weak dynamic spine will strike to the right of your aiming point. That’s because the shaft bends too far around the bow’s riser at release, and is not stiff enough to flex back into its original alignment at the time it was released. A dynamic spine that’s too stiff does not bend around the bow riser enough, and it will fly to the left of where you were pointing it at the time of release. If you’re left handed those impact positions are reversed.
If you are shooting off a fixed arrow rest a weak dynamic spine will also shoot lower than an arrow with the correct dynamic spine; and a dynamic spine too stiff will shoot high. That’s for the same reason as the left or right impact. We often speak of ‘arrow flex’ during paradox but it is actually arrow oscillation, with the flexion occurring in all planes. Thus the arrow not only bends around the riser, it also bends around the arrow shelf or arrow rest.
Here’s the bare shaft dynamic spine tuning process I use, as simply stated as I can manage.
1. Even if you normally shoot with your bow canted, do all bare shaft tuning with your bow held vertically. THIS IS IMPORTANT. If you cant your bow, strong-spine deflection then becomes ‘up and left’, and weak spine becomes ‘down and right’. Trying to separate up and down shooting errors from the spine’s influence is difficult when the bow is canted.
2. The best target for bare shaft tuning dynamic spine is a straight vertical line. A strip of tape on a piece of cardboard works well. I set this to true vertical on a backstop, using a plumb bob. Aim all your shots to align with the tape, as close as you possible can. Try your best to keep your arrow aligned with the tape, left and right. Don’t be concerned about the up and down impact.
3. When tuning dynamic spine, concern yourself ONLY with the left-right point of arrow impact in relation to the tape. Ignore any ‘nock kick’ (to either right or left). If the nocks consistently show way high or way low kick, adjust the nocking point of your string a bit to get them fairly level (up and down). For nocks too high, move your nocking point down, and vice versa.
4. Start out with the total tip weight setup you want to use. For most carbon arrows a total tip weight of around 350 grains will get you well up into the Extreme FOC range. This can be a 100 grain brass insert with a 125 grain point on a 125 grain steel BH adaptor; or any other combination of component weights that adds up to the total weight you wish to use. My “normal” point setup for my hunting arrows is a 190 gr. point (to match the Grizzly), a 125 grain steel BH adaptor with a 100 grain brass insert; for a total point weight of 415 grains. If I use this on CE 350 Heritage shafts or Grizzly Stik Safari shafts, and it gives about 26% to 28% FOC. The Heritage and Grizzly Stik are fairly heavy shafts (in grains per inch). The lighter your shaft (in grains per inch) the higher FOC you’ll end up with for a given point weight. That’s because the shaft’s weight towards the rear will be less than for a higher-mass shaft. A tapered shaft also helps up the FOC. With this point weight on a lighter shaft, such as a Gold Tip Ultra-Light, the FOC is up in the Ultra-EFOC range; above 30%.
5. Begin your bare shaft testing with a full length shaft. Start the testing from up close; about 12 to 15 yards. Shoot a group of shots and see where the group center is, in relation to your tape. It SHOULD be to the right (if you’re right handed). One thing you have to be on guard for here is that when the dynamic spine is WAY off, you can get false readings. These are commonly encountered when you first test, with the shaft still full length; especially the false strong spine impact. They are caused by the back of the shaft striking the riser, deflecting the arrows flight to the opposite direction from where the spine wants to take it. So, apply a bit of consideration of what you SHOULD be seeing initially. If it doesn’t show weak spine (impacting to the right) SUSPECT that the back end of the shaft is slapping your bow and go ahead and shorten the shaft a few times. Often the impact will suddenly jump from a false strong spine impact to a markedly weak spine impact; once the shaft’s rear stops slapping against the bow’s riser.
If you shorten the shaft all you can at this close range and the impact is still showing weak spine (a right impact), then the only cure is to start over with a shaft having a stiffer static spine.
6. From this close range, and assuming you’re not getting a false reading, your bare-shaft arrow should be impacting to the right side of the tape. Begin shortening your full length shaft in small increments. If the close-range dynamic spine is WAY weak I generally take off about ½” to 1″ at a time, cutting from the shaft’s rear end (to prevent having to remove the insert every time the shaft has to be cut), until the point of impact is getting a few inches from the tape. From there on, I shorten the shaft in 5mm increments – about 1/5 inch at a time. Stop shortening the shaft when the point of impact is still about 2″ right of the strip of tape. It’s important to not cross over to a strong spine impact. If you do that, the only cure is to add more point weight.
[NOTE: All parallel shafts can be shortened from the rear, and you’ll not need to remove the inserts to cut the shaft. On tapered carbon shafts you’ll need to make the cuts from the front of the shaft. This requires that you remove the insert before making each cut.]
7. Move back to 20 yards and repeat the process, again stopping when the point of impact shows about 2″ of right (weak spine) impact.
8. Progressively move farther and farther back, repeating the process to as far a distance as you have faith in the validity of your group’s accuracy; for determining the left-right ‘group center’. I tune my bare shafts back to 40 meters, about 44 yards. At that distance I leave the bare shaft group’s center showing about 1 ½” to no more than 2″ of weak-spine (right) impact. Adding fletching will have a slight stiffening effect on the dynamic spine.
9. Now fine tune your nocking point. Do this at fairly close range, about 10 yards, and on a target of uniform density (a fairly new foam-type target). If the nock kicks up on impact, move the string’s nocking point down; and vice versa. Get the arrows impacting with the nocks as straight (level, up and down) as you can.
10. Next, make up some more shafts matching those you’ve tuned and fletch them up. Use ample, but not excessive, fletching size; just enough to be certain it will stabilize whatever broadhead you intend to be using later. Shoot several groups to confirm that the fletched shafts impact into the same group as your bare shafts. If you normally shoot your bow canted, then go ahead and shoot these groups that way.
11. The final stage is to add broadheads onto matching fletched shafts and verify that they also impact the same as your bare shafts and the fletched field points.
The one factor I didn’t mention in the tuning process is that you can also use the degree of centershot on your bow as a tuning aid. Building the riser out (giving it less ‘centershot’) will allow a weaker dynamic spine to tune correctly. When I apply this technique during tuning I simply add layers of masking tape until I get the right thickness. Once I’ve determined the correct amount I peal the tape off and measure the thickness and build the riser out that far. Often all that’s required is a thicker arrow plate.
So far, when I’ve tuned the bare shafts this way I’ve yet to have the fletched arrows (both field points and broadheads) fail to match the flight the impact point for the bare shafts.
Once I have the setup tuned this way I then tune the fletching to give the smallest fletching that will stabilize the broadhead under all shooting conditions. I prefer the A&A fletching pattern, which utilizes a turbulator forward of the fletching. Here’s the process I use to tune the A&A fletching, but the same process works for determining the minimum size for any fletching pattern. Just as when bare shaft tuning, finding the minimum amount fletching is a step by step process.
1. Once you feel that you have the bare shaft tuned correctly, mount a matched-weight broadhead on one of the shafts. First use what you are absolutely certain is ample fletching to stabilize the broadhead and VERIFY that the fletched-shaft/broadhead has identical impact to the field-point tipped bare shaft. You can use any fletching pattern you like for this step.
2. Once your shaft tuning is verified begin, switch to the A&A pattern on the broadhead tipped shaft, starting at about 5” length if you are using 3-fletch, or 4” if using 4-fletch. DO NOT add the turbulator yet. Shoot the arrow several times and check the flight stability.
3. If all is well, begin to gradually decrease the length of the A&A fletchings until the point where you FIRST see a slight instability in the arrow’s flight. Be sure to shoot several shots before making a decision on the flight stability, and it helps if you can have another person also watching for flight instability too.
4. Now add the turbulator and check to be sure the flight is again completely stable. If addition of the turbulator does not completely stabilize the arrow’s flight increase the fletching length by ¼” and check again, with the turbulator in place.
Many factors affect what’s the minimum A&A fletching that will work FOR YOU. A big factor is quality of your release (mine’s poor). Other major factors are the type of broadhead (how much wind shear it generates) and the amount of FOC on the arrow and the shaft’s length. Your draw length on whatever length shaft you are using is also a factor. At a given amount of FOC, the longer the shaft the less fletching required; because of the lengthened rear steering arm. Your draw length vs. shaft length affects the point of maximum shaft flex upon release.
5. Once you feel you have the fletching at the minimum size for stability there’s only one task remaining; you will need to check arrow flight on a windy day. When checking for flight in windy conditions you will want to take shots as many angles to the wind, but at a minimum check the arrow’s flight in a full cross-wind and both quartering with and quartering into the wind. I’ve not found any problem when using the high MA single blade broadheads, because of their very low wind shear factor, but many of the wide-narrow broadheads require an increase in fletching area to achieve flight stability in quartering wind conditions.
This sounds like a lot of work, and it is, but it is a one time job for a given arrow setup. It’s analogous to a working up the very best handload for a rifle; and cheaper and easier to accomplish than finding the best rifle handload too!
Ed
