Stu Miller Spine Calc.?

[goldflinger]

Ok Guys, how long, in inches, does a 75 grain Muzzy brass insert adapter add to the length of the shaft? I assume I use the standard 1" in the footing length of the calculator, but how much do I add to the BOP Length? Thanks in advance for your response!

[xtrema312]

It doesn’t add length to the shaft.  BOP lenth would be nock notch to the back of the adapter part at the end of the shaft.  It adds weight to the insert and point.

Footing would be a good question for Stu.  I don't have a clue exactly how he would figure that one, and I am not sure exactly how he applies the footing section of the calculator.  I have been planning to ask about that.  I kind of think he figures each arrow with a standard to that arrow insert, and then adds footing for the extra.  He could just intert all the length of the insert as footing.  I should run some numbers on an old vs. new calculator to see what works out.  Standard insert vary a lot in length.  I know he uses it for inserts as well as external footing.  

There are so many variables that it is hard to tell how it would work out exactly.  I typically only figure footing for the amount of the insert that is longer than a standard insert.  I find that weight ahead of the shaft has more effect than the same weight in the shaft.  I get real close allowing for that when I have a base line arrow to work from.  I have found that the insert vs. point weight doesn’t change the output if the numbers add up the same. In reality it does change the arrow.   I would guess on that part.  Then start a good amount weak and test a lot then cut a little.

[goldflinger]

Do you know anything about the gold tip screw weights? Do they screw in to the adapter which is glued into the shaft, thereby increasing the length of the arrow? Then I guess you screw in the breadhead to the weight.  Thinking you just screw those into the alum. inserts. I could be wrong and they are screwed into the the back of the insert? Wish I could see these in person to figure out how they work. Not sure if the screw in's go in front of or behind the insert, and if you can screw two together (ie a 50gr. and a 20gr) to make 70 grains.

[xtrema312]

They screw into the back of the insert.  Point screws into the front of the insert.  They add insert weight not arrow length. However, more arrow length and insert weight both weaken the dynamic spine so it is kind of the same unless your arrows are too short.  You can use hot melt on the insert to change stuff or get one of those real long tools to do it from the nock.  I don't fool with them, but I have thought about it a lot.  For the cost of them and all the fuss I would just as soon get a point 25 gr. lighter or heavier or make a change to the arrow length.  They really are only for fine tuning to add a little weight.  80% of the time I end up with brass so they are not useful because I would have to start with the aluminum insert and add a bunch of the weight to get up to the brass one in the first place.

[sffar]

Hello,
I love Stu's calculator. I'm new at this, and with new bows I'm spending a lot of time trying to concoct various arrows for them.
I'm also a bit confused by the insert and footing inputs in Stu's calculator. I find the results can vary a lot depending on how components get defined. I've been including the visible 1/4" of brass insert, for example, into the BOP length, not as part of the point. Otherwise you'd have to guesstimate what each section of the insert weighs. Also, if you leave the insert field blank and just call an insert a footing it gives a different result than if you attempt to add the additional length of the insert as footing. The insert field seems like the hassle as it seems like it makes assumptions I'm unaware of. By playing with these inputs I can sometimes massage results to get what I'd like, but don't know if the result is accurate. The instructions are a little unclear to me on these points. If an insert (if included at all) assumes a length, for example, does it also assume some weight also?
I hope Stu can set me straight on these questions. The calculator's the greatest thing, especially with the cost of components, miscut shafts and so forth.
Sam

[metsastaja]

If using inserts any length over 1 inch the additional length becomes the footing length and a yes should be entered into the footing box.  Do not add any weight as that is calculated in the insert weight.

100g brass inserts measure a total of 1.5 inches so yes would be checked for footing and length would be 0.50
50g brass inserts measure a total of 1.0 inches treat as a insert only

Both inserts extend approx 1/4 inch beyond the shaft and should be included in the bop length.

you can download stu's directions as well as his tips in PDF at    http://www.heilakka.com/stumiller/  
the direction download is just to the right of the calculator download.

[sffar]

Thanks for the link, though I have read the tips/directions and am still a confused over things as mentioned above.
If I leave the insert field blank, enter 1.5" for the footing w/100 grs footing weight I get a different result than putting 100 grs as "insert, then 0.5" (or 0.6") into footing length and zero as footing weight
Glad to hear I was entering the BOP information properly!
Sam

[sffar]

Is this correct?
1) An insert of .9" is assumed whenever any shaft other than wood is selected.
2) Any footing weight, other than for wood, is entered as insert weight.
3) Only for a wood shaft, or perhaps for an additional external footing over any other shaft, is a weight value added for footing weight.
4) Footing length for all shafts other than wood is length which surpasses the automatic .9" insert value.
Thanks,
Sam

[sffar]

Can anyone help set this straight?

[xtrema312]

Stu will probably be along soon to help out.  It is the deer opener so maybe he is out hunting.

[sffar]

xtrema,
Thanks for the info. I've noticed he's usually paying attention when questions come up. First things first!
Sam

[xtrema312]

I have done things a little different in the past, but I tried this with a few arrows that work on my different bows and got really close on the numbers.

Carbon arrows
Put insert weight in insert weight area.  
Input point weight
Arrow length from base of nock to face of insert.
Turn on footing and add or deduct amount insert is different than 1"

I use standard inserts that are all different between CE, GT, and Beman.  Also brass that are 50 and 100.  My 50's are about the same at the CE and GT length, but they are a little different.  100 brass and Beman inserts are 1 1/4".

For external footings I would add only the footing part that is longer than the insert and add the weight as footing weight.  That has been close for me in the past.  However, you need to account for the fact that external footing makes the arrow larger in diameter, and that changes the center cut of the bow a little and stiffens the shaft more than just what the footing number does.

Don't forget  silencers, brace height, bow quivers and the like make big differences.  I got a new to me LB a while ago with good size wool silencers. The arrow I thought would shoot close in it was way stiff 12" at 20 yd.  I took those silencers off and put on some small cat whiskers.  The arrow was then weak about 4-6" at 20 yd.  That is a big difference.  

I also recently realized I was getting lazy with my deep hook.  I tightened that up and notices some dynamic stiffening due to a better release.

[sffar]

Thanks, extrema312. I've started using the same input assumptions you're using. I still wonder about the inputs for footing weight–seems like it can only apply to wood arrows, as the calculator apparently assumes a footing with all other materials (even when left blank). To me a footing and an insert seem like the same thing. I agree that making sure all measurements are accurate and variables accounted for is essential. Besides the examples you gave, knowing precisely how far to center the bow's cut, and the actual draw weight are things it can take some effort to determine. If you used a wood arrow with an extra inch for length, then added an aluminum sleeve to that inch, presumably you'd use the footing length/weight inputs, the insert field would not figure, and the arrow thickness/center cut would remain the same as you'd only be resting the wood against the riser and not the aluminum sleeve. I think! Fiberglas arrows would be another matter!!! Inserts for glue on broadheads would probably have to have the weight divided between insert and point weights
I just want to make sure I'm using the calculator properly.