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Main Boards => PowWow => Topic started by: jkm97 on July 19, 2013, 09:59:00 AM

Title: How much will a 1/2" longer shaft weaken spine?
Post by: jkm97 on July 19, 2013, 09:59:00 AM

My 28" Axis .340 is just a tad stiff with a 75 grain insert and a 125 grain head. In addition, I need a touch more length for broadhead clearance, so I was thinking of killing two birds with one stone. But I'm not sure how much 1/2" will weaken my shaft, and don't want to go too far.

Title: Re: How much will a 1/2" longer shaft weaken spine?
Post by: JimB on July 19, 2013, 10:39:00 AM

A rough rule of thumb would be 1"=5#=25 grs of point weight but the truth is,every setup is different and you would just have to cut one and tune to know for sure.Starting at 28",I suspect a 1/2" difference would be fairly noticeable.Playing around with Stu's calculator might give you a feel for how much that would change things.You would still need to tune to confirm.Good luck with it.

Title: Re: How much will a 1/2" longer shaft weaken spine?
Post by: Easykeeper on July 19, 2013, 11:02:00 AM

If you want to keep the same tip setup, 75 grain insert and 125 grain head, the only way to know for sure is leave them long and slowly cut them back in small sections until you get a good bare shaft tune.  Easy if you have a cutoff saw, less practical if you don't.

If you aren't committed to that exact point weight I would just add the length you need for broadhead clearance and retune letting the point weight fall where it might.  

I wouldn't even hesitate to make a guess on how much longer you need to go, carbons seem to respond pretty quickly to a change in length.  When in doubt it's better to leave them long and cut back...can't put it back on once it's cut off.

Title: Re: How much will a 1/2" longer shaft weaken spine?
Post by: SCATTERSHOT on July 19, 2013, 11:10:00 AM

I doubt you would notice much difference, but if you did you could build out your sideplate a smidgen to compensate.

Title: Re: How much will a 1/2" longer shaft weaken spine?
Post by: Sharpster on July 19, 2013, 11:20:00 AM

I'm with Scattershot... Don't think you'll see much difference at all (if any) with carbons.

Ron

Title: Re: How much will a 1/2" longer shaft weaken spine?
Post by: jkm97 on July 19, 2013, 11:40:00 AM

Thanks guys. I'm close enough that I know I can play with point weight and make it work at 28", but I might cut my finger off with a broadhead attached. 28.5" should work for clearance, and I'll tune with point weight from there.

Title: Re: How much will a 1/2" longer shaft weaken spine?
Post by: Yellow Dog on July 19, 2013, 01:11:00 PM

I've slowly over the last couple of years been dropping in bow weight. I draw 30" and a 31" 5575 Gold Tip worked perfect at 52/53@30. Now that I'm down to 47/48@30 a 32 1/2" 5575 bare shafts perfectly. I'm here to tell you a 32 1/2" arrow with a broadhead on it is a mighty long arrow.