Different Thickness FG Lams On Belly and Back?

[Shredd]

  i may have strict comparisons one or two times...  i can't remember on what...  but on my quest for performance the main thing that stayed a constant was  - my quest for performance -...    funny but partially true...

   my constants were...

  -  limb shape, because i am working on that one design and stuck with that form unless i decide to
        trash it and try another
  -  bows 40 to 45 pound draw, because that is the average weight that men shoot
  -  glass thickness  .040 / .040
  -  profile somewhat but could vary just a bit...  that last bit of sanding could change how your limb
        bends and could nock off 2 to 3 fps...  i have actually had a bow shoot very fast with fatter tips
         and when i sanded them down i lost speed
  -  bow length, riser length

   what i did change and experiment a lot with is taper rates and built in wedges for speed and pad
    angles for stability and quietness....

     once you reach what you think is optimal for that design you could change limb length or riser length or profile and then start all over with your tapers again...

[Roy from Pa]

Rich you have put in a lot time and effort into building fast bows that look awesome.

 

[Shredd]

thanks bro... that means a lot to me...  wanted to quit about a 100 times...  i am a bit of a nutcase / mad scientist when it comes to something i am passionate about... 

   one of my passions now is playing pool and i am working on an invention right now to improve my game...

[mmattockx]

   my constants were...

I was thinking of just for testing the difference between equal thickness lams and unequal thickness lams. Otherwise the options/choices are near limitless.


Mark

[kennym]

I would think same core lams with 40/40 glass vs 50/30 glass would tell the tale.

Maybe when hunting winds down a bit ....

[AndyTurner]

From an engineering standpoint there is no reason to use the same thickness of FG lams on both the belly and the back. The tension side is inherently stable and thinner glass can be used to utilize more of its potential. Yet almost everyone seems to use the same thickness of lam on both belly and back.

Hi Mark. Thank you for bringing this up. I'm new to this but was thinking exactly the same thing.

GC-70-ULZ has a Tensile strength of 243000PSI. Use this for the Back.
GC-70-ULS has a Compressive strength of 119000PSI. Use X2 strips of this on the Belly giving 238000PSI
This in my "simple head" would give you a "Balanced Spring".

Can a grown up confirm/deny if I'm woofing up the wrong tree please?

Many thanks,
Andy

[Flem]

thanks bro... that means a lot to me...  wanted to quit about a 100 times...  i am a bit of a nutcase / mad scientist when it comes to something i am passionate about... 

   one of my passions now is playing pool and i am working on an invention right now to improve my game...

Its a good thing to be passionate about you vocation or avocation. I suppose we all have our own "thing" that gets us excited to build the next bow. Does not really matter what you thing is, as long as you have one. My thing is to build a bow so smooth I have an out of body experience while shooting.

[Shredd]

   my constants were...

I was thinking of just for testing the difference between equal thickness lams and unequal thickness lams. Otherwise the options/choices are near limitless.


Mark

if i knew that and tested that i would have shared my info in the beginning of this thread...   

[Roy from Pa]

Flem..
Your thing is to build a bow so smooth, you have an out of body experience while shooting.

Depends for men can help:)

[Flem]

Well I was thinking more like my consciousness, but since I'm full of dodo, I guess its the same thing 

[Longcruise]

I'm probably in the dark on all this, but my goal is to prevent set or string follow.  I'm playing with more compression resistance than tension.   

[Mad Max]

Well I was thinking more like my consciousness, but since I'm full of dodo, I guess its the same thing 

You do hang up your diapers up on a clothesline

[mmattockx]

Can a grown up confirm/deny if I'm woofing up the wrong tree please?

It doesn't work that way. Stiffness is what you need to balance, not ultimate tensile strength. There is no reason to balance the back and belly lams like that anyway, if one side is stiffer than the other the neutral axis shifts and the bending stresses balance out internally. Also important to note is that compression will cause a failure before tension will, because compression causes buckling failures and those occur well below the tensile limit of the material.

The reason I asked is because we don't get close to really using the maximum available performance of the fibreglass lams in a hand held bow, so better performance comes from finding ways to get a bit closer to the maximum the materials offer. Using a thinner lam on the back will work it harder and get a bit extra out of it (on a per mass basis), while also reducing limb weight some (fibreglass is much heavier than the wood core).

I'm probably in the dark on all this, but my goal is to prevent set or string follow.  I'm playing with more compression resistance than tension.   

The primitive bow flight shooters would agree that minimizing set is very important to maximum performance. I agree that compression is the problem, because tension doesn't appear to cause any form of set. It is all on the compression side that the damage occurs and reduces the performance.


Mark

[AndyTurner]

Thanks Mark, that makes sense.