Stus Calculator

[Aaron2k5]

After using stus calculator for my howatt hunter 55@ 28 with a 29 1/2 inch draw, it says to use a 2117 with 125 grains to put me dead on.  Ive been told to buy 2018's or 2020's and now I'm all confused.  Every other chart ive also looked at says 2117's are way too much for my bow.

Im lost.

[Night Wing]

If you put all the correct info in all of the boxes, it will get you very close to the correct spined tunable arrow where you can fine tune by lowering or raising the brace height. But, if you put in incorrect info, it will throw you off.

Most people input the wrong info (distance) for the strike plate. They're not really sure if their bow is cut to center or if past center, how far past center. They also don't take into account the distance (thickness) of their strike plate.

Example: The shelf on my Blacktails are cut 3/16" past center so my start number is (-3/16). My strike plate's thickness is 2/16" which is really (+2/16). I have to take into account this thickness so the final distance for the input number is (-1/16) for my bows.

[petertschantz]

good point NightWing, and if you play with the center cut / strike plate numbers you can see what  a huge difference they make in the #s.

I've had good luck with the last set of arrows I got based on the calculator. I measured center cut etc myself and the suggested shaft & point are flying great.

Pete

[Swamp Yankee]

Well said and dead on.  
 

Originally posted by Night Wing:
If you put all the correct info in all of the boxes, it will get you very close to the correct spined tunable arrow where you can fine tune by lowering or raising the brace height. But, if you put in incorrect info, it will throw you off.

Most people input the wrong info (distance) for the strike plate. They're not really sure if their bow is cut to center, or if past center, how far past center. They also don't take into account the distance (thickness) of their strike plate.

Example: The shelf on my Blacktails are cut 3/16" past center so my start number is (-3/16). My strike plate's thickness is 2/16" which is really (+2/16). I have to take into account this thickness so the final distance for the input number is (-1/16) for my bows.

[Night Wing]

In my opinion, the "Center Cut/Strike Plate Position" is the most IMPORTANT and CRITICAL box on the calculator. Anyone putting the wrong distance in there is going to have a frustrating experience with an arrow which will most likely never tune (work). Then, they blame the calculator never realizing the incorrect distance they put in the box is the reason why the calculator isn't working for them.

[mrpenguin]

I have a Hunter as well. I input 1/16 past center on Stu's. I am pretty sure that is correct. I also use the "form" adjustment. Basically, I found that with my bow, carbon 500 epics with 175 up front cut to 29" shoot like darts. I adjusted the Personal Form for that to match and then input new arrow data to figure out the woodies.

Hope that helps!

[xtrema312]

The calculator is a start, but doesn't account for all things.  All bows are not created equal just based on type.  I shoot all carbon and suspect some of my experiences are due to the way carbon acts.  

I have had bows that get real close using the calculator, and I have others that do not match no matter how I calculate and tweak it.  My MOAB is about right on.  My new shrew is not even close.  The calculator says it needs 60# dynamic spine and it shoots an arrow at almost 12# lighter than that.  

I have also found that very long overhanging arrows don’t calculate the same as say an arrow with 1" overhang using different points and getting the same number in the calculator for dynamic spine. They just don’t act the same, but they are in the ball park, and I can fine tune for length.  Carbons seem to be very length sensitive.  

In addition, I have found that I can't match between all arrows of the same spine.  Some shafts just act a little different when shot regardless of the listed spine.   I shoot mostly GT 5575 and Beman 400.  In the calculator these are within one pound of the same spine.  In reality I have to have an extra ½” on the Beman or go up about 25 gr. on the point.  Again all manageable, but not exact.  

The calculator is a fun tool and helps, but it can’t account for everything.  Your form is a huge factor as is your release, what you used on your hand tab vs. glove and many other things I have found.  Use it to get close and leave yourself some options on cutting and points.  Then work it out by bare shafting.

[Night Wing]

I don't pay much attention to the Personal From Factor number until I'm through tuning both of my bows. Let me clarify.

I'm right handed and shoot right handed bows with a split finger one over, two under tab. With my 30" draw length, I shoot 32" BOP aluminum arrows. Never shorter, never longer. This is one reason why I don't bare shaft tune. I choose the point weights I want to shoot whether they are 75 grains, 80 grains, 85 grains, 90 grains, 100 grains, 125 grains, etc. This is another reason why I don't bare shaft tune. Stu's calculator does all the bare shaft work for me in one quarter of the time.

I then practice at 5, 10, 15 and 20 yards. If the arrow is hitting slightly to the left (stiff) or right (weak) of where I'm aiming at with field points, I raise or lower the brace height accordingly so the arrow hits where I'm aiming or looking at. When the field points are hitting where I'm aiming at, at these distances, then I remove the field points and shoot the same grain broadhead weight at the same yardages. The vast majority of the time, the broadheads are hitting in the same place as the field points.

Only then do I look at and deal with the Personal Form Factor. This is what I've found with both of my bows.

For my 42# recurve shooting a 2212 arrow with an overall arrow weight of 421 grains, with a 75 grain point weight, my Personal Form Factor is (0). I didn't have to adjust the PFF default number which is (0).

But; for my 37# recurve shooting the same 2212 arrow with the same overall arrow weight of 421 grains, with the same 75 grain point weight, I had to adjust the PFF default number from (0) and my Personal Form Factor number with this bow is (+9).

[Aaron2k5]

The calculator had the preset for Martin hunter. I added .175 for my velcro rest. I did guess at that. I'm at work now but ill try to run it again measuring with a caliper

[Eugene Slagle]

What I had to do was mark the center of the bow to help me determine my center shot location, like on my Zona with nothing on the shelf it is dead center but with the leather plate it sets +1/16, my Sky was way past center so I built it up to get her center with the plate on.

Now both bows with a slight BH difference will shoot the same GT Trads nearly identicle.

[Aaron2k5]

I'm pretty sure my bow is cut to center. I plugged in 1/16 and 1/8 and they both said I needed a heavier spine than 2020.  Should I just go ahead and just buy 2020s? I am very anal and because of it I gave my old arrows away and now I'm not shooting. I need to get back out there before I go nuts!

[Aaron2k5]

I bought the 2117s. I can always weight em down if need be

[Night Wing]

Aaron,

I'd be interested in seeing if the 2117s work out for you.

[Al Dean]

I shoot a pma lll 46# @ 30".  It shoots a
31 1/2" 2117 with 125 bare shaft perfect.
You are pulling 59-60#.  I would think anything over 30" on a 2117 might even be a little weak.

[Aaron2k5]

That confuses me because most people said to shoot 2018 or 2020. And the 2117 is weak?

[Night Wing]

Aaron,

The 2117 is a stiffer arrow than a 2018 or a 2020. The proof is in the numbers. When it comes to aluminum arrows, the lower the number, the stiffer the spine.

According to Easton's charts, a 2117 has a spine of (.407), but has a designation of 400 in a series.

The 2018 has a spine of (.464), which is the weakest of the three spine sizes. A 2020 has a spine of (.426) so it's in the middle.

The 2117 will need more point weight than either the 2018 or a 2020 because it's stiffer.

If it was me with with your 55# @ 28" bow, I'd cut a 2117 to 31" BOP (back of point) since you will be pulling around 58#-59 1/2# at your 29 1/2" draw length. This is predicated on adding 2#-3# per inch past 28".

As for point weight; since I don't know the parameters of your bow or what type of bowstring (fast flight or dacron) and the number of strands, experiment with shooting different point weights like 125 grains, 145 grains, 150 grains, 160 grains, etc. Don't forget about fine tuning by raising or lowering the brace height if the arrow is slightly stiff or weak depending on where you're aiming at 20 yards.

With a right handed bow, to the left of where you're aiming at is stiff and to the right is weak.

[Bud B.]

Kinda. It all depends on your length and tip weight.

The 21 is the diameter of the shaft. The 17 is the wall thickness (thinner than the 2018 and 2020).

Larger diameter means more metal. Thinner thickness means less. Longer means more weight i.e. lesser spine which translates to weaker shaft. So in a sense the 2117s can be weaker in dynamic spine. Shorten the shaft length and stiffen the dynamic spine. Add tip weight and it weakens the dynamic spine as well.

You may know this already but this is how I've decoded the shaft dia/thickness for me. Either way you've got to tinker with something no matter what shaft you use.

Muddy waters shaft dynamic spine is......

[Aaron2k5]

Thanks guys just got back in. I shot 140 grains and left them at 31 1/2 just to start. At 30 yards I shot pretty straight and some knock right. Im going to buy some 175, shoot, and maybe cut a little

[Aaron2k5]

So far cut down to 30 1/2. Shooting great.

[Night Wing]

Looks like Stu's calculator was right when it picked a 2117 for you.