limb profile dimension

[TC209X50]

How much does limb profile width dimension effect weight? For example, if your width is 1.85 at the widest point and you reduce the width to 1.75 at its widest point and carry that reduced amount throughout most of the profile how much will that effect the overall weight?

[mmattockx]

Weight is directly proportional to the width, so if you reduce the width full length by 5% then you will see a 5% reduction in weight.

In your case you would get (1.75/1.85) x 100 = 94.6% of the original draw weight. In reality it will be more approximate than that, because none of the dimensions on a bow limb are that precise in the first place, but it will get you pretty close if you are precise and accurate in your width reduction.

Note that you need to reduce width proportionally, not by a fixed number. If you just take your proposed 0.1" off the whole limb you will change the tiller and lose more weight than planned because that 0.1" is a larger portion of the limb width out towards the nock than in at the fades.


Mark

[kennym]

What Mark said...

[Kirkll]

More important than draw weight,  limb profile shape can have a large impact on a bows performance. Years ago I did a bunch of experiments with RC limbs and different width profiles and came to the conclusion that taper rates and limb thickness are the most important factors for limb stability. Not width....... I also found that I could do a straight taper limb width profile from 1.65 to 5/8" tips and get higher performance with less limb mass in the outer limb. Less hand shock and substantial increase in speed.   Food for though.... 

I would recommend concentrating on where your limbs are bending when profiling the width.  a narrow profile with deeper cores are superior. adjust draw weight with stack height. Taper rates and wedges can help adjust where the limbs are bending too.

[TC209X50]

More important than draw weight,  limb profile shape can have a large impact on a bows performance. Years ago I did a bunch of experiments with RC limbs and different width profiles and came to the conclusion that taper rates and limb thickness are the most important factors for limb stability. Not width....... I also found that I could do a straight taper limb width profile from 1.65 to 5/8" tips and get higher performance with less limb mass in the outer limb. Less hand shock and substantial increase in speed.  Food for though.... 

I would recommend concentrating on where your limbs are bending when profiling the width.  a narrow profile with deeper cores are superior. adjust draw weight with stack height. Taper rates and wedges can help adjust where the limbs are bending too.

Thanks for the input, I added bamboo as a core on this one and missed it. I imagine the difference between the bamboo and red elm probably added about 10# from my estimated stack dimension I'm guessing.

[mmattockx]

I also found that I could do a straight taper limb width profile from 1.65 to 5/8" tips and get higher performance with less limb mass in the outer limb. Less hand shock and substantial increase in speed.  Food for though....

That's no surprise, you just used the pyramid back profile that works so well on wood bows. It makes a great bow with light tips. What did the side profile look like?


Mark