Whats this talk about foam in limb cores

[mooseman76]

Thanks for the info, Bob.  What constitutes a short draw limb for a 29.5" draw?  Maybe better question would be what would be the right length for a 29.5" draw?  Thanks...Mike

[Bob Morrison]

Getting a limb marked for 26" and pulling 29.5". The limb was not built for 29" it may work for 1 arrow or 10000. But you are definatly pushing your luck. Usually 30+ should have over 62" bow with a longer limb.

[amar911]

Mike,

I have the same draw length you do at 29 1/2". I have 7 or 8 Morrisons, some with boo cores, some with foam cores, and some with foam cores and carbon backing. My shortest has a 14" ILF riser with the "C" foam/carbon longbow limbs for a total AMO length of 56". It is a little over 50# and shoots very well for me. I have shot thousands of arrows through it with no problems. It is as smooth and accurate as any bow I have. I have hunted with Bob Morrison with that bow and he agrees it fits me well. I also have the first foam core Shrew ever built -- a Classic Hunter longbow that is also 56" AMO and a little over 50#. Both these bows are among the best I have ever shot, as are other foam core bows I own. You don't have to use a lengthy bow at your draw length, but you must pick carefully to get the right design in a shorter bow. Try to stay with a "C" limb or longer in a Morrison at your draw. If you want to be conservative but stay fairly short, a "D" limb on a Mini-14 ILF riser gives you a 58" bow that is very smooth to more than 30" and shoots like a dream. Either the foam/carbon longbow limbs or the foam core recurve limbs will perform similarly; it just depends on your personal preference as to which works best for you.

There is everything right with the top actionwood and actionboo core bows like the Bracks, but even the great bowyers like Bill Howland recognize some of the desirable qualities of the synthetic materials. The important thing is to buy from a top notch bowyer who uses what he knows will work well and then stands behind his products. You can't go wrong with guys like Morrison, Howland, Coffey, Johnson, Sarrels, Holm (just to mention a few) and a number of the other top bowyers out there who make the beautiful bows we shoot.

By the way, I agree with Bob Morrison about the concept of giving away bows for testing. We have the best test crew in the world here at TradGang, and we spend our own money to buy the bows to do the tests. We also have the largest audience, thanks to Terry and the moderators. I like the idea of the bows going to a paying customer or a worthy cause of the bowyer's choice.

Allan

[Sid]

Here are our observations.
 
We have been making ILF target limbs for about 25 years and bows since 1940 and composite cored limbs for around 12 and so we have some experience. Here are our observations and thoughts.
 
Twelve years ago we started looking at composite cores as they were though to be the pinnacle of limb development. Syntactic foam was being used. Syntactic foam is used as a void filler in composite mouldings most commonly used in boat building it is not specifically intended to be temperature stable and can be worked in several ways. It can be in expanding form or inert.  You take a resin normally epoxy can be another and a light weight powder consisting of micro glass spheres. The spheres I assume have a gaseous core and so are light weight and you mix these to the resin until you get the characteristics you want weight versus strength.
 
The resin normally has a density of 1.1 or there about and hard maple although it varies is normally quoted at 0.72. And so you mix the microshperers to get what you are looking for the more you add the lower the mass you get and the weaker the material becomes. Getting below 0.72 density become problematic as the materials ability to withstand compression and it also becomes weak and brittle too many spheres and too little resin. And hence some of the observations noted.
 
We did not use Syntactic foam for our products but a solid epoxy matrix that is designed for temperature dimensional stability. It has a density of 0.55 or 23% less than Maple and I say this as it seems to be a great weight saving but I also have to point out that this great saving is from the lightest part of the limb structure and so you have a big saving of very little. The other point here is that you have to make massive savings in limb mass to gain very little extra arrow speed. and so we see speed improvements over maple of only 1 to 3 FPS depending on bow weight bow length and drawlength.
 
As far as meaningful speed measurements you can easily loose 3 fps on bow tune and limbs to make specific weights can be fat on tolerance or skinny on tolerance and so easily 2 fps can vary on the same limbs same weight and length. and so comparing limbs to define a 2 fps advantage is not that convincing The 2 fps is there but you may not record it. If it is two different limb models the brace height changes etc etc etc all contrive to motivate a wrong conclusion.
 
Which is best for what purpose
 
If you are shooting 6 dozen arrows at 90 meters, you are looking for consistency and dropping your arrow group 2" or 3" at that distance can easily cost you the competition and so temp stability is a definite plus.  Shooting one arrow only at up to 40 yards on unmarked distances now how can you tell where the advantage is and 2" variance at 90 meters is insignificant to 20 and 40 yards and the difficulty in estimating yardage is even less consistent and so what is the advantage???  If you have dollars to burn then by all means go for the absolute but for me and all practical considerations you are not handicapped at all practically by going to a quality high performance limb with a wood core for hunting and all unmarked distance shooting. Don't get me wrong the higher the price tag is always the salesman game but not always the customers benefit.
 
Smooth draw.  We can find absolutely no difference in the DFC between wood and composite the DFC is dominated by string angles and that is controlled by the shape of the limb. There is a consideration that core tapers can affect this but when put to the DFC you are not able to make  a perceptible difference. If there is no difference in the DFC then the limbs draw equally.
 
Durability
 
This in practical terms seems to be equal with the material that we use and I would assume Syntactic foam. In the bow limbs the material is in the neutral axis and protected  by the bow facings and so it works well. Comparing the materials out of the limb the wood is much more robust.
 
These are our experiences we make about 1000 bows per year and have so for the last 10 years or so all types from self wood bows to Olympic target limbs.
 
 
Sid

[SteveB]

Great info Sid.

Thanks
Steve

[Bob Morrison]

We don't build anyways near 1000 bows a year. All the experts have voiced there opinions.We all win,everyone has another choice,be it foam cores, different carbons or some majical new design.A year ago then I was try to find foam cores to try I couldn't get it anywhere and Then I find a bowyer that had it and none to share. After a long hard try I got some made for me, used it for several months and after few other USA bowyer wanted to try it. Thats when I Got with OMC so others could try it. It is available to everyone now, not cheap, but you can get it.

[vermonster13]

You done good Bob. Thank you for not being afraid to experiment and push on.    

[Hawkeye]

My hat is certainly off to all of you who keep trying to improve what is available and are willing to take the time, trouble, and expense to figure it all out.

Seems like all you have to be is an engineer... and a lab technician... and an artist... and a scientist... and craftsman... and an inventor... and, well, more stuff than that!

Thanks to all who make the bows that help keep this SO interesting!

Now, back to my secret work on the "water limb core."    :eek:    Not going too well so far!!  ;^)

Daryl

[Ron LaClair]

It's human nature to push ahead to continually try to build a better mouse trap.     That's how the compound bow got developed, but as it turned out instead of a mouse trap it was a rat trap...    

My hat is off to you Gentleman...  

[Ron LaClair]

Bob Morrison has always been willing to share his ideas with Gregg and I...sometimes it takes a little doing to get him to open up. At the Expo last month I had to bribe him with buffalo sausage to get him to tell us some trade secrets....  

[O.L. Adcock]

Well said Ron, Sid, Bill, Bob,and you, all good folks trying to do something that isn't easy!   ....O.L.

[Ron LaClair]

trying to do something that isn't easy!  ....O.L.

I think that's what drives us folks in traditional archery...the fact that it's NOT easy. In my case I've always taken the harder road. It's more  challenging and a lot more FUN.    

Here's a quote that I like that may be appropriate here.

  " There is a destiny that makes us Brothers,
  No goes their way alone.
  All that we send into the hearts of others
  comes back into our own"

[Bill Howland]

I'm with Big Ron on this one: Bob's good folk. The set of foam cores that I laid up came from Bob's inventory. Get this...He sent them to me no charge. I didn't feel right about that so I did send him a check for the cores not knowing how much they are. Bob, Did I send enough? Hope so and thanks for your help. One thing I'd like to address though...above you mentioned the experts have given their opinion. I'm Surely not an expert!

Gotta also say thanks to OL..He's helped me a lot over the years with my small brain teasers, bow designs and has never ask for anything in return.

Larry Hatfield if you're lurking thanks for your help and chats also.

Dave and Beth Windauer deserves a thank you also. Along with countless others out there that have taken the time from their busy schedules to chat with me about bow designs, processes, finishes and business in general.

But you're right Ron, I think it's very important to share information back and forth. We just don't have the man hours being smaller shops or the funds to do all the projects that are running through our minds. And if someone has tried something that I've been thinking about why recreate the same process via trial and error. When good folks out there are willing to share their experiences. Just not enough time in a day to do all.

Just hope one of these days I can help folks with what I've learned.

Thanks guys!      

[Bill Howland]

As I think about this! Some of the most important folks I need to thank are my customers over the years!      

If I didn't have their support and push to make the best bow I know how for them I certainly would not be here today!

Thank you!

[amar911]

Talk, talk, talk. Bill, get off the computer, get back in your shop, and build my bow!!!!!!!!!!!!                    

Allan