Arrows - too stiff or too weak?

brman

Member
I got my wife a flatbow for her birthday and volunteered to make some arrows for her (my first attempt at making arrows). All went well and she said they shot fine.

Except.......
I noticed there was a slight (but not terrible) fishtail and, more importantly, noticible marking where the shaft was hitting the bow (shelf upright protection piece). There were two marks, both very obvious (already wearing the varnish) and around 3 inch long. One about 6 inch back from the point and one just in front of the fletchings. Both the opposite side of the shaft from the cock feather, hence my assumption it is from the upright, not the shelf.

I have already canvassed opinion at the club but it would be nice to have some more opinions before I make yet more arrows!
So, spine too stiff or too weak?

I have deliberately not said what poundage bow etc as I am curious what people say with just the above info ;)
 


Timid Toad

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Sorry, need more info than that. Definitely either too stiff or too weak, but either can produce those results.
 


brman

Member
Sorry, need more info than that. Definitely either too stiff or too weak, but either can produce those results.
ok. I was hoping there would be an indication which way just based on the symptoms but it sounds like not. So... more info.....
The bow is a 62" flatbow, roughly 29lb at the fingers and just shy of 29" draw length. As best I can measure centre cut is around 1/8".
Arrows are spruce shafts, 5/16 dia, 30-35lb cut to 30inch (nock to end of shaft) with 3" feathers and 70gn points. Crude measurement of their spine (26" supports, 2lb weight) puts the shafts used in the 30 to 32lb range.
However I have found using this info a bit confusing. Most charts I have found would say they are too weak but if I put the figures into the 3riversarchery online calculator it suggests I actually need a weaker arrow. The centre cut figure makes a huge difference to the result......
 


JamesP

New member
Running through the numbers off the top of my head, that information makes it seem like they're probably slightly too weak, but I could be wrong on that front. I'm no expert when it comes to wooden arrow spines, and I'll admit that for the little spots of traditional archery I do - I prefer carbon.

Although, since you're making the arrows yourself, it might be worth making some extra for experimenting with high/low point weight and longer arrow lengths to find out what works best - longer lengths and heavier points weaken the arrow, and shorter lengths and lighter points stiffen it.

Yes, where the shelf is cut will have an effect on the tune, and some bow/arrow combinations will tune easier than others. It's always fun to experiment and find out. Good luck!🏹
 


Timid Toad

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Yes, I'd suggest weak. Go up a spine but cut them longer and be prepared to shorten as necessary.
 


brman

Member
Thanks Guys,
A guy in the club has volunteered to bring down a few varying spine arrows for my wife the try, that way hopefullly I can get the right spine without making too many arrows ;)
 


iandall

New member
Tuning to eliminate fishtailing and clearance are two different (but not independent) things. You choose the spine of the arrow to get it coming straight out of the bow. Clearance comes from synchronizing the speed of the arrow with the vibration frequency so that tail end of the arrow is at maximum deflection away from the riser at the time it passes the riser. Unfortunately this is hard to do. Luckily this sychronization doesn't have to be perfect - so long as there is clearance with a bit of margin, it doesn't really have to be maximum clearance. Also luckily, commercial arrows tend to work. If you are lucky, changing spine will get you something which is both matched to the draw weight of the bow and gives adequate clearance.

If not, you need to change the vibration frequency or the speed of the arrow. In which direction, I can't tell. You can change the vibration frequency by changing stiffness (spine) or arrow shaft weight, but the correct spine is determined by the bow and its draw weight and generally the shaft weight is determined by the spine so usually little room to move here unless you change materials or method of construction. You can speed up or slow down the arrow by changing point mass (with minimal effect on tune). You can have stiffer, and longer arrows, which will have the same tune and more mass to slow the arrows down, or less stiff, shorter arrows which will have less mass to speed them up.

You don't need to worry about the contact near the point, that is expected as the flexing arrow gets driven into the riser. Also, how good is your wife's form? That can definitely have an effect.
 


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