Draw pull

[bow101]

Just wondering about this draw spec. A buddy of mine sold a bow he built, cherry backed with hickory.
Long story short it was a 58 35# 24"... Shot about 200 times. Sold the bow to a young lady, apparently she shot it a few times and then pulled it back t0 about 28 inches and the bow broke.

My question is what really is the threshold of a bow considering all the factors like final tillering. ?
Is a bow supposed to pull way over the maximum draw..in other words if a bow is tillered and rated at 26 inches will it and should it pull to over 30 inches..?
This question has been mystifying me ever since i took up this hobby....!!!!!

[sleek]

A bow is designed to be pulled to a certain distance and then stop, exactly there. A bow can be pulled further, and most the times ends up like that ladies bow, splinters. Wood can only take so much stress before it gives, and good bows are usually built right up there on its limits to get the most effeciency and still be safe. Once overdrawn, 28 inches on a 24 inch bow, all bets are off. Its amazing she was even able to pull it that far before it broke. Hopefully nobody was hurt?

[PatM]

The draw length isn't really "designed" into the bow quite so specifically. You have to experimentally break a few bows to realize that most will break far beyond their designed draw length, particularly if the bow is broken in a bit rather than pristine.
 Most would agree that a 58 inch bow drawing 28 is pushing the limit but the bow may have been fine at 26 forever.
 It sounds more like she needed a bow of longer draw and heavier weight.

[bow101]

Then tell me in a few short sentences the proper tillering process getting to the limit..?
As for the questions about the lady pulling the bow, don't know much other than she is on the robust side...)

[sleek]

To get a bow to its limit, use the mass formula.

[PatM]

The mass formula may optimize efficiency of materials but it won't tell you when the bow is gong to break as you overdraw it.

[Pat B]

Bows, especially wood bows are tillered to a specific draw length. That bow should not be pulled beyond that point. You can always tiller out farther(within reason) so it will pull farther safely.
 An old archery addage is...a bow fully drawn is 9/10 broken...meaning if you pull it to 10/10 it will break or at least get badly bent.
  When you tiller a bow you want the limbs to bend evenly and together as you achieve the draw weight you desire at a specific draw length.   Different back profiles with have different bent profiles, some bend in the arc of a circle, some more eliptically and some have more hybrid shapes.

[Del the cat]

We've had this question before of course, and I've even asked it myself!.
I'd say that 1" overdraw from your stated length is a reasonable compromise to allow for assorted variables like weather, string being maladjusted etc.
So... I test my bows very briefly to 1" over, so a 28" draw bow gets pulled to 29".
The above is a good reason to only shoot arrows that are as long as the stated draw (measured to the base of the point).
If a bow is made to be 28", but is expected to get pulled to 30" on occasion for flight/demo/stupidity purposes it must be made and tillered out to 30" (maybe plus 1") for safety else it will just go bang or take a load of set.
My first decent Yew longbow is now over 35 years old, it's only about 70" ntn, originally tillered to 28".
I've pulled it to 31.5" just for the heck of it, accepting it was risky, it took some extra set and now is 68# at 28" not the 75# it once was, (still a fine bow).
Del

[jimmy]

This is something I've never really understood either.  I understand not pushing a certain length of bow past a certain point or poundage.  But if say a 64" osage bow is tillered to my 27" draw at 55#, that's just the weight I want at my draw length.  There is nothing stopping me from pulling it to 28 or even 29", it just goes up in poundage.  I don't see that there is much if any stress overload on a bow that is built to safe dimension, even if overdrawn.  Now on a 48" or 55" bow, or something of that sort, it might be a different story.

[PatM]

I definitely think people are deluding themselves a bit about the science of tillering to a specific drawlength.  Yes, you have to be pretty precise to hit specific poundage at a set draw length but that has little to do with  maximum drawlength and weight or the point the bow will break at.
 Most bows are considerably longer than needed for safety and as Jimmy says you could just draw them further to hit a higher weight.
 I have an Elm recurve that I usually draw 27.5 for regular shooting and I routinely crank it back to 32 when flight shooting it. It just bends further and pulls a heavier weight.

[JW_Halverson]

To misquote a wonderful post of Del's, "pull it until it breaks, then back off a bit."

I often use the basic principle of building a bow's length to be double the draw length plus 10%.  For my own draw length of 26, that would be 57.2" between the nocks, allowing for a stiff handle and fadeouts.  When I write "X lbs  @ 26 inches" on that bow, it should be a clear indication not to pull past 26 inches. 

But AMO standards require the bow to be marked with the draw weight at their standard length of 28 inches.  So non-primitive archery types tend to be confused with my marks.  They are used to walking into a bow shop and pulling something off the shelf and believing it is safe at all draw lengths.  My 57.2" bow could be pulled to 28 and suffer set, or I could overbuild and add another 4-6 inches of length so that in case the person overdraws beyond the 26" the bow would not suffer much. 

Ultimately, building a bow for someone is a nasty gamble, especially if they aren't well versed in primitive archery.  They will hand the bow to a 6'9" gorilla and blame you as they are pulling bloody splinters out of his forearm and left eyesocket.  I tell everyone that their bow is built to "their individual specifications" and that once it leaves my hands there is no warranty, expressed or implied.  I further tell them that it will break some day, and the more they let someone else shoot it the sooner that day comes.  And lastly, this is why I chose to not seek to become a professional bowyer.  I refuse to expose myself to that level of liability.  Because if I get sued and they take my modest investment in hand tools, my 13 yr old jeep, and my coffee can of loose change (mislabelled 401 OK) then I got nothing left.

Your mileage may vary.
 

[ionicmuffin]

i always build my bows with room to spare, for instance, my draw is 29.25" and so i would never build anything much less than 66" although a 60" bow might make it to 29 if tillered correctly, if not then who knows, i really think that you make it for that person, or to be used by people of near similar draw. I did take the bow i made for my sister(currently 24" draw) and made sure the arrows were no longer than 25" to avoid anybody overdrawing them, and it worked! people cant overdraw what isnt there!