Adjustable string nock, spine, deflection etc

[GrahameA]

Afternoon All

That is the reason why the compounders always have to have pressure buttons against arrows ....]

I don't. I use a drop-away and if you apply any side pressure to the arrow it will fall off the rest. (Even a strong wind will blow it off the rest.)

... build yourself a spine tester.

Now there is a really good piece of advice for those who want make their own arrows ... or modify arrows the already have.

[Dennis La Varenne]

Fanto,

I hope i am not annoying you with all this discussion about bow setup! I dont just sit and meddle with these bows and nothing more - I do shoot huge numbers of arrows each day and im striving for better and better shooting.

Absolutely not. It seems to me that there is a great deal of information 'out there' which, for some reason, makes the fundamentally simple business of shooting an arrow at a mark into something fraught with complications.

The science surrounding the how and why of archery is detailed and fascinating, but somehow, many people seem unable to distil basic principles from that knowledge and end up not being able to see the forest of information is made up of individual trees. In the modern enthusiasm for acquiring huge banks of knowledge, people seem to lose sight of the fact that actually shooting a bow is a fairly simple affair requiring a fairly basic knowledge set.

Very few archers these days understand the basic principle of controlling the paradox phenomenon by having something against which the passing arrow must push itself away. The basic principle requires that for an arrow of given spine, the degree to which the arrow plate is positive (wide of the bow's centreline toward the arrow) is what actually controls how the arrow leaves the bow. It is the combination of spine AND positive arrow plate which controls arrow flight, NOT spine alone which is the mistake commonly made.

They go to the spine charts, read up on the required spine for that draw weight/draw length/arrow head mass combination and completely ignore quite innocently, the crucial importance of how much side pressure the arrow plate puts against the arrow as it launches and instigates the paradox bending. That side pressure is completely passive because in a conventional trad bow, it cannot be altered easily short of packing it out or rasping some off.

That spine jig article I posted is based on an arrow plate cut no deeper than the string line which means that the arrow point on such a bow will always lie outside the string line at brace height. Hence, the principle that for every 1/8 inch further outside the string line (away from the arrow plate), the required spine of the arrow is reduced (bigger number) by one spine grading (5 lbs).

After that beginning, for every 10 grains extra head mass greater than 125 grains, the required spine must be increased (smaller number) by one spine grade. For practical purposes, each spine grade is equivalent to 50 thou.

So, the process is -
1. You select the nominal spine grade from the charts I supplied above which are based on a 125 gn head mass and a 28 inch draw length;
2. Using the figure worked out from 1. above, you then assess how much the arrow plate of your bow is outside of centreshot and allow one spine grade for each 1/8 inch (about 2mm) outside centreshot;
3. Using the figure worked out from 2. above, you then increase or decrease that spine rating by one spine grade for every 10 grains greater or less than 125 grains head mass.

So, applying the above for an exercise - Joe Blow has a 50lbs long bow and draws 28 inches. His bow is outside centreshot by 1/4" and he wants to use a 200 grain head (because he is a great fan of high FoC), so

1. Nominally, he requires and arrow which bends 650 - 640 thou on the spine jig (assuming the arrow has a 125gn head).
2. Because his bow is 1/4 inch outside centreshot, he will need to drop his required spine down by 2 spine grades (100 thou) to approximately 750 - 740 thou.
3. But because he wishes to use a 200 grain head, he will then need to increase the spine rating of his shafts calculated at 2. by around 7 spine grades (350 thou) to around the 400 - 350 thou mark.

TO INCREASE SPINE GRADE - SUBTRACT THE NUMBER OF THOU. TO DECREASE SPINE GRADE - ADD THE NUMBER OF THOU because more thou equals more bend or less stiffness and fewer thou equals less bend and greater stiffness.

If Joe was to alter his draw length different to 28 inches, that would have to be taken into account at stage 1. of this calculation. Every inch of draw length change requires one spine grade decrease (bigger number) for every inch shorter than 28 inches and one spine grade increase (lower number) for every inch longer than 28 inches.

This process may spin your head a bit at first, but once you get the hang of it, it is not very difficult. BUT, SO YOU DON'T CONFUSE YOURSELF, YOU MUST FOLLOW THIS SAME PROCESS FOR EACH AND EVERY BOW. You also need to get your head around the concept that increasing the spine grade means that there is less deflection, which means that the spine number is smaller, not bigger.

If you do a few hypothetical calculations as an exercise, you will soon get the hang of it, but I repeat, you must follow the same sequence in the calculations or you will get nowhere except profoundly confused.

All of this above applies to a minimum required spine rating for a bow held vertically. If you cant your bow, then you will find that you can use shafts greatly in excess of the above without problem. I use my spine jig these days only to see what is going on or for testing purposes or to ensure that all of my shafts are the same stiffness. Long ago, I realised that so long as my shafts could stand in my bow, I had no problems.

(I need a cup of tea.)

[Fanto]

Gday Dennis

cheers again for the insight. I printed out and made up the sliding spine chart, and I plan to make a spine jig and thereafter, some dowel arrows.

Just for interest's sake, I compared Stu Miller's calculator results with the AMO chart, (i worked with a 50lb recurve, cut 1/8 before, B50 string on Stu's)

Change___AMO___Stu
1" draw___5.5lb___5 lb
10gr___1.5lb___2.5lb
1/8___n/a___8lb


regards

Fanto

[Dennis La Varenne]

Fanto,

Let's see how things work out for you.

Nobody knows why Kev Whiting and John Ursem designed this jig based on 27 inch supports when there was already an international standard based on 26 inches, but that small problem can be got around easily enough.

[discord]

Possibly a stupid question, but does shaft diameter make a difference to this calculation? It seems to me that the centre of a small diameter shaft would be in a different position to a larger one when they sit against the plate...

[Fanto]

Discord

Stu's calculator takes diameter into account. That is all i know on the subject.

(It may seem I am "singing the praises" of this calculator, Im not. Just an observation)

[Dennis La Varenne]

discord,

This is the kind of technical nitpicking which I was referring to earlier. People invent problems for themselves which just aren't there. For practical purposes, unless you are an olympic grade shooter in the top dozen or so international shooters - ignore shaft diameter. The quality of your loose will give you far more problems than the diameter of your arrows every time.

I commented on increments of 1/8 inch or close to 2mm requiring one spine grade allowance.

Just think through what you are proposing for a minute.

If you go from an 11/32 (8.73mm) shaft to a 23/64 (9.128mm) shaft, you have a diameter which is 0.398mm greater. That difference in shaft diameter will move the centre of a 23/64 shaft 0.199mm further out than an 11/32 shaft.

Just how do you propose to allow for such an incredibly small amount as that and be able to tell the difference for any practical purpose?

It just doesn't matter.

[discord]

lol, I'm still using the cheap carbons that came with my first bow... I only asked out of curiosity. I haven't used wooden arrows, but was thinking more of the difference in carbons, where there can be up to 5mm variation.

Anyway, stupid question status confirmed

[Dennis La Varenne]

discord,

If what you say is correct about the variation in carbons, I still would not concern myself unless the 'half-diameter' is 2mm or greater. As with woods, small differences in diameter have a much greater effect on spine rating and that would be a primary concern. I suspect also that on a bow of constant draw weight, I would be surprised if you are going to be using arrows with up to 5mm diameter (2.5mm half diameter) from the one bow.

[GrahameA]

Hi Dennis.

This is the kind of technical nitpicking which I was referring to earlier. People invent problems for themselves which just aren't there.

It gives them excuses.

The quality of your loose will give you far more problems than the diameter of your arrows every time.

Dennis you can say that a 1000 times and most people will still not take any notice. Evidence suggests that a bad release will cause a variation of up 20fps on 50 lb bow.

[scuzz]

Dennis you can say that a 1000 times and most people will still not take any notice. Evidence suggests that a bad release will cause a variation of up 20fps on 50 lb bow.

That is interesting evidence. I shot a trad bow for a constant 5years with quite a bit of practice, and i cant say i ever thought of improving my release. Something to keep in mind! Thanks.

Scuzz

[Fanto]

I dont think we could have de-railed this thread any more comprehensively, even if we set out to do so!

[Buranurra]

I dont think we could have de-railed this thread any more comprehensively, even if we set out to do so!

No dramas to me I am very happy for the thread drift, as there are plenty of gems in the responses.

[GrahameA]

Afternoon All.

lol, I'm still using the cheap carbons that came with my first bow... I only asked out of curiosity. I haven't used wooden arrows, but was thinking more of the difference in carbons, where there can be up to 5mm variation.

My questionable mind finds that variation between carbons perplexing. Can you back that claim up with some numbers?? Perhaps running a Micrometer over a dozen shafts would be interesting to get an idea of the variations in a set of the "same" shafts

The 2012 Easton catalogue does not quote a tolerance for shaft size and experience suggests that they usuall are with a few thou of their quoted size. The best I could find is that they offer that their carbons are straight to +/- 0.003" which implies that their tolerances are fine. (They go finer if you want to pay more.)

CArbon Expree run their shafts out 3 decimal places - so one would expect variation of half a thou.
http://www.carbonexpressarrows.com/arch ... ws/nano-xr
http://www.carbonexpressarrows.com/arch ... ws/cxl-pro

For Dennis The catalogue also gives spine deflection values

For those who would like to read the catalogue it can be downloaded from here: http://www.eastonarchery.com/downloads

[little arrows]

When custom making arrows the diameter of the arrow is not the main criteria to set for an arrow. The shaft spine comes first followed by the weight. The diameter can vary slightly when a micrometer is used. However choice of timber dictates the final weight and diameter. Steve may make a set of 5/16 Oregon shafts that are spined to 65# or 70# and weight 560gn. The next set may be Hoop Pine 23/64 spined at 40# but weight only 390gns. The shafts are custom built to suit bow weight and draw length. He tends to build durability into a beginners arrow by making them thicker, not necessarity heavier, and people don't understand that. They just see a thick shaft and presume it is heavy when it may not be. I am only speaking for custom made arrows that are done here, not mass produced arrows, purchased in store.
I have no experience with aluminiums or carbons, so can not help in that area.

cheers
sue

[greybeard]

For what it is worth the following arrow [wood] charts are from the AMO standards 2000 edition.

AMO Spine Selection Charts..doc

(123.5 KiB) Downloaded 116 times

Daryl.

[Fanto]

Afternoon All.

lol, I'm still using the cheap carbons that came with my first bow... I only asked out of curiosity. I haven't used wooden arrows, but was thinking more of the difference in carbons, where there can be up to 5mm variation.

My questionable mind finds that variation between carbons perplexing. Can you back that claim up with some numbers?? Perhaps running a Micrometer over a dozen shafts would be interesting to get an idea of the variations in a set of the "same" shafts

The 2012 Easton catalogue does not quote a tolerance for shaft size and experience suggests that they usuall are with a few thou of their quoted size. The best I could find is that they offer that their carbons are straight to +/- 0.003" which implies that their tolerances are fine. (They go finer if you want to pay more.)

CArbon Expree run their shafts out 3 decimal places - so one would expect variation of half a thou.
http://www.carbonexpressarrows.com/arch ... ws/nano-xr
http://www.carbonexpressarrows.com/arch ... ws/cxl-pro

For Dennis The catalogue also gives spine deflection values

For those who would like to read the catalogue it can be downloaded from here: http://www.eastonarchery.com/downloads

The difference in diameter in question refers to the different diameter shafts available which have the same spine, for example compare the indoor target carbons which are .421 dia compared with the easton axis and also Beman shafts which are .250 dia.

surely carbon shafts of the same model and spine are all the some outside diameter +/- 2/5ths of 4/8ths of stuff all

[GrahameA]

Morning.

The difference in diameter in question refers to the different diameter shafts available which have the same spine, for example compare the indoor target carbons which are .421 dia compared with the easton axis and also Beman shafts which are .250 dia.

Comparing different models/brands of shaft is not a valid comparison. It is like comparing shafts made from WRC with those made from Ironbark.

surely carbon shafts of the same model and spine are all the some outside diameter +/- 2/5ths of 4/8ths of stuff all

IMHO they are even better than that.

However others have claimed

... I haven't used wooden arrows, but was thinking more of the difference in carbons, where there can be up to 5mm variation. ....

[discord]

The difference in diameter in question refers to the different diameter shafts available which have the same spine, for example compare the indoor target carbons which are .421 dia compared with the easton axis and also Beman shafts which are .250 dia.

This is what I meant... Should have been more specific

[GrahameA]

The difference in diameter in question refers to the different diameter shafts available which have the same spine, for example compare the indoor target carbons which are .421 dia compared with the easton axis and also Beman shafts which are .250 dia.

This is what I meant... Should have been more specific

Understatement of the Year.

As an example, Which Beman Shafts are you talking about?? Different purpose arrows come in different sizes eg Beman Flash compared to Beman Hunters. Both Carbon with different intended end use and production methods.

Have a look http://beman.com/shaft-selector/

[Fanto]

Possibly a stupid question, but does shaft diameter make a difference to this calculation? It seems to me that the centre of a small diameter shaft would be in a different position to a larger one when they sit against the plate...

Discord,

I understood exactly what you meant when you wrote about a small diameter shaft versus a larger one. small dia shafts include easton Axis, Beman MFX etc large Dia are the X-cutter goldtips etc and the .300-.320 such as goldtip trads are the mid or standard diameter carbons.

cheers

[discord]

That is the reason why the compounders always have to have pressure buttons against arrows ....]

I don't. I use a drop-away and if you apply any side pressure to the arrow it will fall off the rest. (Even a strong wind will blow it off the rest.)

I'm a bit reluctant to bump this 'heated' thread to the top again, but regarding this, Dennis, the Easton tuning guide says that arrows of compounders using release aids (as opposed to finger release) bend vertically, so the nodes stay in alignment down the centre of the string. This alleviates the need for sideways pressure.