SBO 2022 - The Tailgate Trifecta

[RichterScale]

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"

I ended up stopping and renting a floor sander on the way home from work and then spent the evening sanding a floor.
I still plan to test a few different carbon shafts. If not tomorrow then over the weekend for sure. I even have some small free weights in the garage that the stepson left behind. I don't have any of the CF stiffeners made for necks, so hopefully someone has some and can do a bendy test.
What's the diameter on the crossbow bolts?
I've never used a crossbow, but I thought they used a shorter, larger diameter shaft than a typical bow(?)

 

[RichterScale]

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?

I'm no expert, but the gist of it is that they wrap resin soaked CF strands around a tube, bake it, pull it off the tube, grind it and polish it. There's a lot of "top secret" propriety methods that the arrow makers don't divulge. But they basically wrap the fibers at an angle and change the angle at different points of the shaft to create more or less stiffness/flexibility and strength at different points. The rabbit holes are deep in archery.

 

[AK4570]

Deep rabbit holes indeed... and perhaps more myth than truth.

These are .350 diameter

 

[NKBassman]

@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.

All my engineering textbooks are at the office and I'm working from home today, but I would assume that a solid rectangular beam would be better at resisting bending than a hollow tube. However, it will be highly dependent on the specific geometry of the cross sections (ie beam depth/width VS tube diameter/wall thickness).

 

[Durham52]

Does that mean I now must recant my position and instead advocate for aluminum?

Kidding. Aluminum works fine, and is nice and light. I used it once instead of a truss rod (shhhh, don’t tell anyone).

Nothing wrong with that, back in the late 70's I did a few electric guitar necks with two aluminum stripe in them, sort of aiming for a poor mans Kramer, or Travis Bean, but without the cold feel of the aluminum coming through the wood. I still have one of the guitars, it's been fine all these years. (I also did one with brass strips imbedded. Hey, everything was brass back then! I can safely say that all it added to the guitar was weight....)

 

[NKBassman]

Nothing wrong with that, back in the late 70's I did a few electric guitar necks with two aluminum stripe in them, sort of aiming for a poor mans Kramer, or Travis Bean, but without the cold feel of the aluminum coming through the wood. I still have one of the guitars, it's been fine all these years. (I also did one with brass strips imbedded. Hey, everything was brass back then! I can safely say that all it added to the guitar was weight....)

Were the aluminum "stripes" visible in the neck, like laminations between wood? That would look pretty cool and would probably add a lot of stiffness. Just need to make sure that whatever glue you use provides good bond between the wood and the aluminum.

 

[AK4570]

@NKBassman , I agree with your theory that the beam would exhibit greater stiffness than the tube, dependent, of course, on wall thickness, strand orientation, etc. Additionally, a CF "beam" closely encased in wood and affixed with epoxy should demonstrate even greater resistance to bending forces.

All of that to say that I do not have any CF "beams" but do have some arrow shafts that may (or may not) get inlet into a second neck beam and bolted onto a body for testing purposes. Since the extra neck blanks I have laying around the shop are 5-piece laminations, it's anyone's best guess what they will add or detract but which does make for some interesting discussion.

Thanks again to everyone that contributed theories, thoughts, and experiments

Best regards,
John

 

[RichterScale]

Even if a CF hollow tube didn't add any stiffness to the neck, it would be a good way to reduce weight in the neck and not lose strength.
You'd essentially have 2 hollow, CF lined chambers in the neck.
Although, by the time you epoxied the tubes into the neck, the weight might add back up to the original wood removed.
The larger diameter the tube, the bigger the weight savings. Although I'm a little skeptical of .350" (almost 3/8). That seems large for either side of the TR, unless the neck is super wide and thick, no?

 

[Flamingo21]

I am working in a position with an organization that brings me more joy than I’ve ever experienced in a job prior.

I’m having more fun and living a better “me” than I can ever remember being.

This makes me so happy.

 

[NKBassman]

@NKBassman , I agree with your theory that the beam would exhibit greater stiffness than the tube, dependent, of course, on wall thickness, strand orientation, etc. Additionally, a CF "beam" closely encased in wood and affixed with epoxy should demonstrate even greater resistance to bending forces.

All of that to say that I do not have any CF "beams" but do have some arrow shafts that may (or may not) get inlet into a second neck beam and bolted onto a body for testing purposes. Since the extra neck blanks I have laying around the shop are 5-piece laminations, it's anyone's best guess what they will add or detract but which does make for some interesting discussion.

Thanks again to everyone that contributed theories, thoughts, and experiments

Best regards,
John

It's an interesting experiment and I'm curious to see how/if it comes together. Carry on

 

[RichterScale]

I'm done working for the day and home. Unfortunately, I couldn't avoid a bunch of physical labor today,....sooo, as I lay here and recoup for a bit, I'm trying to build an experiment in my head for later.
A cantilever test is good and easy to do, but I'd also like to test the arrows in a config that simulates weight pulling in the same direction as string tension. And use much more than 5 lbs.
Give me a few hours to come up with something and post pics of broken CF arrows and CF splinters stuck in my hand.

 

[TFM94]

Even if a CF hollow tube didn't add any stiffness to the neck, it would be a good way to reduce weight in the neck and not lose strength.

That's true. The purpose of CF is not only to make the neck stiffer, but to replace some wood in the neck with something that is not susceptible to humidity and temperatures. Despite it's great strength/weight ratio solid carbon fiber is still much denser than wood, so using tubes is an excellent way to save weight. I have used 1/4" hollow square tubes in the past and I suppose the 3/8" arrow shafts would work well.

 

[boxerrider]

A cantilever test is good and easy to do, but I'd also like to test the arrows in a config that simulates weight pulling in the same direction as string tension. And use much more than 5 lbs.
Give me a few hours to come up with something and post pics of broken CF arrows and CF splinters stuck in my hand.

I've done similar tests by hanging a five-gallon bucket in the middle and adding water to it. I was testing to failure, so I poured water in until it failed then weighed the bucket.
A board behind the shaft with a ruler clamped to it would be sensitive enough to provide meaningful measurements.

 

[BishopJP]

Everything I "know" about carbon fiber is based on what I understand of what someone else has told, so "grain-of-salt..." and whatnot.

Seems to me that a carbon fiber arrow shaft, split length wise and epoxied into a neck underneath the truss rod would be a good way to stiffen a neck. Maybe?

Otherwise, it seems like a 3/8" tube would get awfully close to back of the neck.

In any case, I look forward to seeing the results of the experiments!

 

[RichterScale]

Well, a bit of a buzz kill. I have a whole heap of different brand and size shafts from over the years. Even some I experimented with that are something crazy like 1/2" diameter.
That heap is not here. I do have a bunch of finished arrows for shooting, but don't want to destroy them, or rip the fletching off, etc.
So, I took the 2 slimmest arrows (.265" OD, roughly 1mm wall thickness) and clamped vertically in the the vice at the 24" mark.
I'll need to built an actual jig to hold these things, but for now, I learned that there are 3 sections: we'll call it head, mid, tail.
It's stiffer in the head section and flexes more at the 2/3 point between the mid and tail. And it deflects roughly 8" before it doesn't want to go any more. I'll have to make a jig to see exactly how much weight it takes to deflect 8".
I wish I had some CF bars made for necks to compare.

 

[AK4570]

@RichterScale can you post a picture of your setup? It would allow us to potentially conduct similar test in a roughly standardized manner.

And if not, no worries!

I think I'm going to proceed with installing a couple in a 34in scale, Stingray style 5-string neck and go from there.

 

[RichterScale]

Yeah, I just clamped one in the vise and basically just pulled on it. I want to drill holes in wood blocks so I can put the block in the vise and stick the arrow in the hole. I'll do that tomorrow and snap some pics.
These shafts are pretty stiff. The ones I tested are designed to be shot from a 55-70 lb compound bow. 70 lbs is what it takes to pull the bow back. The force exerted on the arrow when the string is released is mind boggling. I can't imagine a little flat stock of CF being stronger than one of these arrow shafts. The big factor here is the volume they take up in the neck.
They do flex some, but always want to go back to straight. And being glued and locked in place inside the neck, I can't imagine they wouldn't add at least some strength.

 

[AK4570]

I concur. Win, lose, or draw. And, since they're made almost totally from salvage wood and a couple pennies worth of glue along with arrow shafts that came out of the trash, the only real investment is time I would have spent doing this stuff anyway.

Ain't science fun!?

...OK, ok... I guess I'll have to include a truss rod and some fret wire as well.

 

[1n3]

Interesting thread. Puts my crappy "workshop" in better perspective. I salute your ingenuity.

Re: carbon fiber vs aluminum stiffeners... Having been around pedal steel guitars with aluminum necks in cold winters, it comes to mind that aluminum's coefficient of thermal expansion is a lot higher than wood. Don't know the numbers for a cf composite, but I'd bet it's closer to wood. Not claiming that's relevant in this use.

The most appealing idea I've seen on stiffening comes from Bruce - stuffing a slot with tow fiber and epoxy. Haven't tried it myself, but sounds pretty cheap & simple.

 

[Durham52]

Were the aluminum "stripes" visible in the neck, like laminations between wood? That would look pretty cool and would probably add a lot of stiffness. Just need to make sure that whatever glue you use provides good bond between the wood and the aluminum.

No. I didn't have the aluminum showing through, I left between 3 and 5 mm of wood, allowing for the taper from nut to heel. I scored the aluminum sides to give the glue a little extra bite and roughness to cling on to and used epoxy to glue them in. The only example I still have is 44 years old and still solid. I agree, the deeper the strip/rod is the better, at least in terms of resisting bending forward under string tension. depth equals strength and rigidity under those forces. adding two strips in a multi lam neck, with opposing growth ring/grain directions, makes for a pretty twist resistant neck too.