Help with selecting spine using Stu Miller's V2 calculator

[rodlonq]

Hopefully some of you have been over the ground I am covering now and all comments/advice will be appreciated. I have seen many references to Stu Miller's dynamic spine calculator on Ozbow so I thought it must be worth giving it a go.

I have most of the values I need on hand but I am a bit baffled how to treat my points. I would like to use a combination of a 50 gn aluminium glue on - screw in adaptor with a 125 gn broad head or field tip as required. I would like to practice with my hunting arrows without damaging sharpened broad heads or smashing the target butt. (see attached picture - note, broad head not sharpened yet).

ScrewInAdaptorPic1.jpg (70.08 KiB) Viewed 1168 times

Note the balance point (centre of mass/gravity or COG) of the two options is only about 1/8" apart. The adaptors are 1 1/2" long and set the tip of the points about an inch forward of a traditional glue on point. I would assume that regardless of calculated FOC the two options should fly much the same?

Perhaps some of you have used the calculator before for a similar purpose and have some feedback, please.

Would it be more"correct" to assume the assembled adaptor and point is the "point" with 175 gn weight? or would it be more correct to assume the adaptor is part of the shaft and only the screw in tip is the "point". I am a little confused with the definition of the "back of the point or BOP". Is an arrow similar to a bow in that the "back" is away from the archer and so the BOP is the very tip of the arrow - or is the BOP the transition where the glue on adaptor or head meets the wooden shaft.

If the latter is true then would the BOP measurement be taken to the start of the adaptor or to the start of the point?

If the former is true then the calculation of FOC uses the total arrow length, as Jeff C. has pointed out many times is a more meaningful measure of FOC. Because of this I am guessing the latter is true, however, as I said, I am confused by the unclear reference to the "back" of the point.

The difficulty in separating the point and adaptor in the calculator is there is no "box" in which to put the mass of the adaptor when dealing with a wooden shaft - it is not the same as an insert used with a hollow carbon or ally shaft where the mass of the two are superimposed.

As always the proof will be in the pudding, but I need to make a decision on what shaft spine to try first. I know it is good to have a go at tuning using various lengths of shaft, spines and point weights etc. however it is much easier and cheaper to front load the process with a calculated estimate done during lunch breaks. Hopefully the very first selection will be the right one at the target butt.

Cheers........ Rod

[Stickbow Hunter]

Rod,

BOP has always meant where the point starts (closest to the archer). I have never used adapters but with your example I would say BOP would be at the start of the adapter and I would include the weight of the adapter as part of your point weight just as the ferrule is part of the broadhead weight. Not sure if that is how to use that calculator but that is how I would do it.

Jeff

[Dennis La Varenne]

Crivvens, syntharrows are so complicated. I think I will stick to my Bunnings hardwood dowel.

[looseplucker]

Crivvens, syntharrows are so complicated. I think I will stick to my Bunnings hardwood dowel.

I've made some damn nice arrows with that stuff. Last lot was overspined but I left them a tad longer.

For the synthetics there is this programme called Bill Bowe - I send him an email with all the parameters and he tells me what I need.