SBO 2022 - The Tailgate Trifecta

[RichterScale]

I was actually wondering the same thing, as I have tons of carbon arrows shafts.
My assumption is that they wouldn't serve the purpose well, as they're hollow and flexible. Where as a solid rod or TOW laid in resin would end up much stiffer.
Plus, the arrow shafts are much bigger, requiring much bigger channels and material loss in the neck, making their flexibility even more of a handicap.
That's my theory.

 

[AK4570]

@RichterScale , that was my initial thought as well. Alternatively, a carbon shaft is (should be?) stiffer than a similarly sized cylinder of maple... I think. Also, these are .350 crossbow shafts so slightly less than 3/8 diameter. My thought was to bed them into round-bottomed slots in the neck blank using epoxy and then affix similarly shaped filets of wood atop of them/the whole rigamarole...

But I'm more than happy to have my completely unscientific thoughts shot down in flames during discussion rather than ending up with a neck that folds in the middle.

Embarrassing doesn't quite cover that eventuality

 

[2groggy]

This needs testing. Or at least thinking about posting about testing.

 

[boxerrider]

Can you split the arrows and then laminate the halves together?
Go from this O, to this ( ), to this ((

I have no archery experience. Are carbon fiber shafts really stiffer than the wooden ones, or is their advantage light weight and stability?

 

[RichterScale]

Are carbon fiber shafts really stiffer than the wooden ones, or is their advantage light weight and stability?

Typical CF advantages. Strength to weight ratio. Different stiffnesses/spine strength for different poundage bows can be controlled easily in the manufacturing process. Straightness tolerances are more controlled and within smaller ranges too.
Also, it just about takes shooting one into a concrete wall at 300 fps to get it to fail.
Cutting them is messy and splintery. Cutting them lengthwise would be a nightmare.
Even the super skinny shafts seem a bit large to fit into a neck. Plus they flex.
I'm assuming they flex a lot more than the solid carbon rods/bars made for neck stiffening.
All that said, I'm a big fan of experimenting.

 

[Max Bogosity]

A hollow cylinder is a great shape for resisting bending from any direction, but it’s mostly wasted in a case like this where the stress is always in the same direction.

Boxerrider’s suggestion is a good one. If you split them into even narrower strips they’ll be nearly flat and easier to bury in a straight flat slot close to the back of the neck.

 

[boxerrider]

I agree with experimenting as well. I don't want to be the one to split them apart!

 

[RichterScale]

If anyone has CF neck stiffening rods/bars that are in the 28-30" range, maybe we can devise a simple test. Clamp it in a vise at one end and hang a specific weight at the other and measure how much it bends(?)
Then I can do the same with a few different size CF arrow shafts when I get home later.
Then compare.

 

[2groggy]

If anyone has CF neck stiffening rods/bars that are in the 28-30" range, maybe we can devise a simple test. Clamp it in a vise at one end and hang a specific weight at the other and measure how much it bends(?)
Then I can do the same with a few different size CF arrow shafts when I get home later.
Then compare.

Also test wood of the same length and cross-section for comparison.

 

[RichterScale]

I think I have some maple dowels that are a similar diameter.
Also, I think a better test would be to support both ends like a bridge and hang a weight in the center. Then measure next to a straight edge.

 

[2groggy]

I like your first idea better. Stiffness would be the same for the combination of material, cross-section, and grain orientation. It's easier to measure the deflection of a cantilever than a 3-point bend because the deflection would be larger.

 

[RichterScale]

Fine. You don't have to yell at me

 

[AK4570]

I was in a.meetong so @RichterScale beat me to it... I would love to see some experimentation along these lines and would be happy to contribute as I'm able.

I do agree that bridge-type deflection measurements would best reflect what we are trying to accomplish.

Here's my parameter proposal: end points at 24 inches, 5lbs of free-hanging weight, right angle deflection measurement.

I'll get onto it shortly with the shafts I've got and report back.

 

[2groggy]

I just tried. The dowel broke because of grain runout.

Edit - Before the dowel broke, it was clearly more flexible (ie less stiff) than the arrow.

 

[AK4570]

Run-out. There's a variable I didn't account for...

 

[ctmullins]

Run-out. There's a variable I didn't account for...

So true. You never know when @2groggy will just "run out" and try it before you get a chance!!

 

[AK4570]

Double entendre... another variable unaccounted for!

 

[BishopJP]

Is the intent to use the arrow shafts on either side of the truss rod like the CF stiffening bars?

Also, I don't have any experience with CF arrows, are they made from a CF weave or a multi-directional laminate? I'm guessing the laminate so they don't explode under compression?

 

[Max Bogosity]

I did a cantilever bend test with the bamboo I used in my EUB, compared against cedar and maple rods of the same cross-section. Cantilevered partially because the greater deflection makes it easier to measure (as 2groggy said), and partly because it more closely resembles the intended application -- a neck is supported at one end and loaded at the other.

 

[AK4570]

@BishopJP , in answer to your question: yes, if these crossbow shafts prove worthwhile, they would be inlet into the neck in the normal position(s) on either side of the truss rod.

Based on the limited testing that others are reporting, it appears as if they may actually provide some limited reinforcement, although I would love to see a deflection measurement of the carbon fibre "beams" sold for the purpose to be able to quantify (obviously on a limited scale) each design's ability to resist bending forces.