Face or back

[EvilDogBeast]

Flem, it's kind of a half and half venture.  We have a fully equipped sheet metal shop, complete with 12 foot power shears, brakes, and presses.  Our career field also encompasses all of the composite and paint work for the aircraft.  The pictures from the bow swap last year are taken inside the paint hangar for the C-17, to give you an idea of what we have available.  We are able to utilize the shop space and equipment for small tasks as long as we provide all of our own labor and materials.  The graphite pre-preg we have can't be used on aircraft once it expires, so it will technically be trash or used for training projects.  For the things I can't do at home I can most likely do at work.  This was more necessary in previous years because I was building bows in my garage.  We bought a bow sho.. err.. house last year so now I have my own space to work, and will probably only paint at work now.

[Longcruise]

Since life forms are carbon based, doesn't a osage self bow have a higher percentage of carbon than a glass bow?   

[Roy from Pa]

Since life forms are carbon based, doesn't a osage self bow have a higher percentage of carbon than a glass bow?   

Just don't you worry about that ole timer...

 

[Longcruise]

Since life forms are carbon based, doesn't a osage self bow have a higher percentage of carbon than a glass bow?   

Just don't you worry about that ole timer...

 

Just got outta bed.  Kept me awake till 5:30 AM. 

[Flem]

Chris, I have been trying to figure out how to incorporate pre-preg into a lay-up. Then I re-read your post.
So you cure it first, then incorporate it into a lay-up?
 

[EvilDogBeast]

You can do it both ways.  It really depends on what is easier for you to work.  For instance, if I am rebuilding a honeycomb panel with full thickness damage I will typically pre-form and cure the patches first.  Once that is done I can bond them to the part as needed without having to worry about the plies sliding all over the place.  This also prevents me from having to build ridiculous vacuum bags that end up sucking my repairs through the damage cutout.  If it's just damage to one face I'll cut, stack/orient my plies, and bond them to the part in one shot since there is nothing else to mess with.

It really boils down to an ease-of-maintenance type thing.  The only downside to pre-curing is you then need to use a separate adhesive to bond it to something else.

I really enjoy composite work as you may have gathered.  Feel free to ask whatever questions you may have.  If you want to see pictures of the non-bowyer related work we do here, PM me your number and I'll text some your way.

[Longcruise]

Chris, I have been trying to figure out how to incorporate pre-preg into a lay-up. Then I re-read your post.
So you cure it first, then incorporate it into a lay-up?
 

What would be the advantage of prepreg over hexcell?

[williwaw]

Here's a question that I've been trying to muddle through on my own.   I'm not going to throw my opinion out there because I'm more interested in the opinions of our esteemed conclave of Bowyers.

This is in regard to glass/wood lam bows.

Which side of the bow should be optimized for to obtain highest performance?  IOW is it better to have more tension than compression or vice versa.   Or, should the two be in perfect balance?

What do you think and why?

upon giving the original question some thought and research, perhaps one should minimize the amount of glass used, ie as little as necessary, which might be a different amount for the face or back.

https://www.tradgang.com/tgsmf/index.php?topic=156814.msg2706768#msg2706768

I asked the same question to Bingham Projects a little while ago because I was unsure about it and am planning to build a glass lam recurve.

Here is the response I got from them copy/pasted:

"Thanks for your e-mail.  For a given limb thickness, there is no difference in draw weight with different thickness of glass.  If the total limb thickness is the same, the weight will be the same.  The best way to most closely hit draw weights is to use a micrometer to measure your limb thickness.  If you measure to .001”, then your weights will be pretty consistent.  It will never be 100%.  There are always those bows that surprise you but the vast majority will be pretty consistent."
https://www.tradgang.com/tgsmf/index.php?topic=147846.msg2573501#msg2573501

[Mad Max]

Why doesn’t someone build a relatively simple bow. Perfectly flat limbs, with a perfectly centered riser. .040 glass one side, .030 other. Cut string grooves so bow can be strung and drawn either direction.

And before anyone says it........I have time to think about, not to do it.

Bvas is the smartest one here

[Roy from Pa]

Bvas is the smartest one here..

LMFAO

 

 

[Flem]

Brads suggestion is a good one, but it only addresses a small segment of the question. I agree with Willie, perhaps we should be custom tuning the amount of laminate we are using. Do we really need a composite with 120,000psi compressive strength when a couple of classic woods like Osage and Yew, proven over thousands of years, come in at around 1/10 of that strength?

Chris, I have been trying to figure out how to incorporate pre-preg into a lay-up. Then I re-read your post.
So you cure it first, then incorporate it into a lay-up?
 

What would be the advantage of prepreg over hexcell?

Mike are you referring to Hexel honeycomb? Maybe Chris can shed some light. I don't know about pre-preg because I don't have the facilities to pressure cure the stuff at elevated temperatures for hours.

[mmattockx]

upon giving the original question some thought and research, perhaps one should minimize the amount of glass used, ie as little as necessary, which might be a different amount for the face or back.

Yes! This is why I asked about using different lam thickness a while back. The back should need less glass to carry the loads than the belly and you always want to minimize the limb weight. Since glass is approximately twice the weight of wood, using the smallest amount of it possible seems like a very good idea.

One other thing to consider (Alan Case has mentioned this) is the strains on the core wood. Thicker glass lowers the strain on the core, while thinner glass increases it. So going too thin on the glass can cause problems with set.

Like almost every real world design problem, there are a bunch of competing factors to balance off and a careful compromise is required to maximize performance with longevity.

Brads suggestion is a good one, but it only addresses a small segment of the question.

I would like someone to explain what they expect that experimental bow to demonstrate? Unless it is heavily strained to near failure I wouldn't expect it to shoot any differently either way. I'm willing to make one but it will be a while before I am set up to do that.

Do we really need a composite with 120,000psi compressive strength when a couple of classic woods like Osage and Yew, proven over thousands of years, come in at around 1/10 of that strength?

Do we NEED it? Of course not. Yew, osage, ipe and the various junipers are all great bow woods that perform extremely well. But glass bows can be strained to significantly higher levels than any wood can be. This allows different limb profiles and a bit higher performance than wood bows with greater consistency and reliability and less tillering skill required to get there.


Mark

[EvilDogBeast]

What would be the advantage of prepreg over hexcell?

Sorry I missed this yesterday.  I'm not sure what hexcell is.  The career field is littered with trade names, do you have a picture or a description of what it is?

[Flem]

"Yes! This is why I asked about using different lam thickness a while back. The back should need less glass to carry the loads than the belly and you always want to minimize the limb weight. Since glass is approximately twice the weight of wood, using the smallest amount of it possible seems like a very good idea."

"Do we NEED it? Of course not. Yew, osage, ipe and the various junipers are all great bow woods that perform extremely well. But glass bows can be strained to significantly higher levels than any wood can be. This allows different limb profiles and a bit higher performance than wood bows with greater consistency and reliability and less tillering skill required to get there."

Mixed messages

[mmattockx]

Mixed messages

Can you explain what is mixed?


Mark

[Flem]

Sure, so if using the "smallest amount of it (glass) possible" equates to no more than necessary, then the excessive strain which can be sustained is rendered moot.

[mmattockx]

Sure, so if using the "smallest amount of it (glass) possible" equates to no more than necessary, then the excessive strain which can be sustained is rendered moot.

Hmmm, how to explain?

Many glass bows are very overbuilt, that would be where using less glass would have a benefit. It would be optimizing the amount of glass needed for that particular design.

On the other side of things, you can design far more extreme bows using glass than with wood, which is where the ability to survive higher strains can be used.


Mark

[Longcruise]

Mike are you referring to Hexel honeycomb? Maybe Chris can shed some light. I don't know about pre-preg because I don't have the facilities to pressure cure the stuff at elevated temperatures for hours.

No I was referring to the 45/45 weave that you illustrated from envision composites.

Managing set in wood/glass ASLs is what got me thinking about the "face/back" question.  With thick cores, I think the use of glass thicknesses that are are appropriate for given bow weights in r/d and rc bows is reducing the glass wood ratio to a point where set becomes inevitable.   You will see it on many if not all "hill style" bows.  Sometimes it's a smooth arc resulting in a string follow effect and often it's abrupt in the face area.

It's not that they aren't good bows,  but any time the bow gives up preload to set it results in a loss of efficiency.

I have an unfinished bow on the bench in which the belly glass is enhanced for a kinda unscientific test of the concept.   We'll see,  but about the only thing that can be actually measured with certainty is the change in profile.

[Mad Max]

This one is for roy.
Remind me not to click on this topic again

[Roy from Pa]