Over Drawing and tillering for safety?

[bushman]

I have read in a few different places that guys will tiller their bows an inch past the intended draw for safety. And also that everyone says not to overdraw a wood bow past its draw length. If you have a properly made bow that has a good tiller at its intended draw and the bow is of a design and wood that allows for longer draws why can’t you draw that bow past the draw length where it was tillered at? Like a long bow for example that was say tillered to 26 inches and is perfect, why can’t you draw it to 28 inches?

As long as you work the bow to its new draw slowly by drawing it to intervals of the draw you want, do you have to tiller it?

I’m asking because I want to make a EWB that will pull 100 # at 28 inches and draws whatever it does at 31 inches. So can I just tiller it till it is 100# at 28 inches then exercise the bow slowly until it reaches a 31 inch draw as long as the limbs are bending the same?

What is the exact definition of tillering? Does it just mean remove wood from limbs until they are bending evenly?
Thanks
Bushman

[Bevan R.]

Many wonderful bows have been destroyed by drawing them a couple of extra inches. some survive but take extra set. Some show no effect at all. but there is a saying, a drawn bow in 90% broke. Sometimes it does not take much to trip that last percentage to 100.

[osage outlaw]

I think you are looking at it backwards.  Tiller the bow to the farthest it will ever be drawn.  Then you can draw it shorter than that with no problems.  If you want to draw a bow to 31" then tiller it to 31".  You can still draw it to only 28" if you want, it will just be a lower weight.  The length of the bow will have a lot to do with draw length. 

[Weylin]

I see your point though Bushman. I'm no expert but my understanding is that you don't have to remove material if the tiller still looks good.   So when you're tillering a bow "past" your intended draw length for extra security you are essentially just carefully bending it out to the new length, exercising it as you go, and carefully examining the bend, only taking off material if hinges or stiff areas emerge at that new length. I think that the type of wood, design used, length of the bow and the draw weight all dictate what a bow can truly handle in draw length. As long as all those factors allow you to continue bending your bow without damage it should be fine. I think the advantage of tillering it past your intended draw weight is knowing with some certainty that your bow can go that far instead of finding out when some big neandrathal yanks your bow back to 30". The risk is that you never know for sure what a bow is capable of. It could have been just great at 28" but some hidden flaw would make the bow blow at 30". I think many people choose to not tiller past what they themselves will pull because they don't want to take that risk. That's all just my opinion, I'd be happy to hear if more experienced people disagree, or anyone for that matter. 

[bushman]

Thank you everyone for the replies. Yes, I guess I was lookin at it backwards. When I wrote that I couldn't think how to get it into words what I was tryin to get at. Weylin, you answered it pretty good as to what I was tryin to ask.

Like I said all I have read on tillering and extra, is to have a draw weight in mind at an intended draw length but as I said I know I want the bow to be 100 # at 28 inches but I want to make to also draw 31 inches but I don't know what draw weight it will have at that draw length, if it is 130 # that is fine with me.

I guess I was tryin to ask if I do get it to 100# at 28 inches what do I have to do to get it to 32 inches and x draw weight? Thanks.
Bushman

[Pappy]

Once you get the 100 @28 just keep going,not sure on a bow of that kind of weight how much it will gain per. inch,most will pick up 3 to 4 lbs. pre inch of draw so using that ,the bow would wind up between 112 and 116 at 32 inches. 
   Pappy

[crooketarrow]

  To draw a wood bow 28" @ 100#'s is a whole lot. To tiller it to 31" you'd have to make the limbs so wide and thick that mass would take over and slow it down and it would take on a lot of set and straing follow if not tillered to the tee. You can always draw passed the intented draw lenth. But like I said this cruchs wood cells. Which causes set and string follow.
   I'd tiller it to 28" or the draw lenth you wanted and not hand my bow to anyone. I use to do as said and tiller my bows a inch passed. And this is good for saftly but bad on cast. By putting exture stress on your limbs. Better to tiller it to the leanth you want and not let anyone draw your bow. Or have a arrow cut to lenth with a head on it so it can't be over drawn.

[Pat B]

My draw is 26". When I build a bow I tiller it out to 28" to be safe. If someone picks up my bow and draws it they are more likely to pull it to at least 28" and I want to be sure it can take it. So, when I write 55#@26" the bow is actually tillered out to about 61#@28".
  The draw weight of a bow is basically irrevelent unless you are selling the bow. I build my bow to a weight that is comfortable to me. Also scales are not all the same. 55#@26" on my scale apparently is 61# 0r 62#@26" when I use someone elses scale.

[bushman]

Thanks for the info everyone. Crooketarrow, wouldn't an EWB pull 100 # at 28 if they are going to pull 120 to 150 + at 32 inches?
Also I'm still trying to understand how it works if you over draw a bow past tiller that is crushes wood cells. I get why it does because of the extra stress on them.
But what do you do during tiller that prevents the wood cells from crushing during normally drawing to its intended draw?
I know I keep rewording the same question but I can't seem to get it through my thick head what I'm tryin to understand. Hope I aint driven you guys nuts.
Bushman

[Pat B]

Bushman, you educate the wood cells to compress and recover by gradually removing wood from the belly so the limbs bend evenly and together. With each wood removal you exercise the bow 20 to 30 pulls but not(never) beyond the ultimate draw weight. This exercising registers the wood removal so you can continue safely. Work slowly, remove wood thoughtfully, exercise plenty and check the tiller. Continue this until you hit your draw length. Hopefully you have excess weight that you need to reduce. If everything is still good shoot the bow a bunch. Check tiller as you shoot to be sure it doesn't change. If it does, you still have excess weight(I hope). After you put 100 arrows through your bow, sand it to remove tool marks and to give you a smooth finish. Be sure all sharp corners are rounded and seal the bow. You are ready for whatever now! d;^)

[Buckeye Guy]

The lbs you pull to draw a bow cause a certain amount of stress in the wood the more wood you can stretch it over the less stress per inch of bow
The stress on the wood causes the belly to compress and the back to stretch . So now if you pull farther you are putting more stress on each inch of bow and the wood is compressed and stretched to the new poundage .so if you have your bow worked down to be as efficient as possible at your draw and lbs and draw it farther you just way over stressed it and most likely it will break ! If you want a bow for a longer draw build it for that draw and just know that when drawn to shorter draw it is just not as efficient as it is at the longer draw !
I hope this helped if not when I get time I will try again to aswer you ? ! there is a lot going on inside our bows it takes awhile to discuss it all!
 Guy

[Del the cat]

It's pretty much all been said.
I tend to test my bows very briefly to 1" past the quoted length if they are going to go to someone else.
That way it's unlikely to blow up on 'em.
I think a 1" safety margin is a reasonable compromise, it also allows for shooting arrows which are a tad overlength to allow for one head snap off and replace (which is fairly common practice amongst UK field archers)
As an example the last big bow I did was for a guy who wanted 90# at 28". I tested it to 29" but I'm pretty sure it would go out past that, but there was no point in risking it as it could introduce set or blow up (it had some filled knots).
If you are making the bow, it's up to you do define it's working limits (hopefully they are within the bows capabilities...)
I had one blow at 26" last week when I was trying to get it out to 28". If It had survived to 28" then maybe 29" would have blown it, but I wouldn't have wanted to hand over a bow that didn't have the 1" safety margin)
Should add 1" safety margin at 28" is ok... but at lower draw lengths maybe a lower margin is appropriate?
I'm making a 1/2 scale ELB at the moment... that won't have an extra inch or even 1/2 "!
Del

[Badger]

Same as Pat, I draw 26 but tiller my bows out to 28. You can destroy the performance in a bow by overdrawing even if the bow still looks fine and hasn't taken too much set. I did quite a bit of testing on bows starting at 24" and then drawing further and further checking arrow speed as I inched up in draw length. Once you do this you become very concious of drawing further than you need to.

[PEARL DRUMS]

 I like that explantion Badger. I feel that a bow tillered to 28" that blows at 29-30" had a problem to start with, or the design was pushing the envelope in a big way. A properly tillered and designed bow should be able to handle a draw length of +/-  1 - 1 -1/2" in my opinion. 

[crooketarrow]

  Theres nothing wonrg with tillering to 28 if you draw 26 for safty reasons. I just quit doing it. Although tilling past your intended lenth might not seam to hunt your bow. It is but the exture stress on your limbs. It's like this a 26 in draw say 50 #'s if you tiller on past 2 inchs to what ever the #age comes out to be. Thats 2 inchs of stress not needed all though it might not seams to hunt your bow. Your would shot smother,faster and have better cast than if you tillered it those exture 2 inchs.

  Pat has it right the tichet to tillering in SLOW. I tiller this way it gantees you to go slow. I take a penical and color in the bows back and then file off with a fine rasp. This grantees to file off the same amont each time. When you see a stiff spot I color in only those spaces file look it needed color in and file again. COLORING IN WITH A PENCIAL MAKES SURE YOU FILLE OFF THE SAME AMOUNT ALL THE TIME. If I have areas I KNOW WILL NEED MORE FILEINGS I'll color in those area draker or color in with a sharpy. Which sinks down in the wood father takeing more fileing to remove the color. This is away of elimating stiff spots you won't over file and get hindges and if you use a tree with a pully system. You can get the correct draw weight to the right draw lenth EVERYTIME. NO GUESSING or trying to build a bow my demintions.