Excel bow mass program

[Badger]

   Willie, thats a good question. When working with a long string you can't use a set amount of deflection as your base because it all depends on how long your string is, if your string is haging down 6" it will register a lot different with the same amount of deflection than it will if it is hanging down 1". I have seen where guys have figured that out and posted it but I never have done that I just go by feel. The longer your string is the higher it will read. I think Jawge might talk about that on his web site. If not I am sure someone else will come along and give you a rule of thumb you can work with. Almost everyone new has the same issue. I just checked a finished 50# bow, the string was hanging down to the 8" mark with my finger just taking out the slack, I pulled it to 23" to get enough bend to brace the bow and it was reading 40#, so for a straight bow I would say about 50# is where I would have first braced this one. The draw weight your bow is reading has a lot more to do with the string angle than it does how much the limbs are bending.

[willie]

Badger

I checked a lighter bow the same way and the results were similar. So if I follow the guideline to never pull a bow beyond it's intended final draw while tillering, then I quess the bow should be 90% done before I try to brace it?  I have read where many boyers have said that they are pretty much done once they have a nice brace. If this is so, then most of the art of tillering is floor tillering?

willie

[Aussie Yeoman]

I haven't done floor tillering in over ten years.

My approach to long string tillering is a little different.

I start with a stave that's bandsawed out to dimensions that will bend a few inches. I use a long string that is just barely long enough to reach over both nocks and pull no further than intended draw weight. As the amount of deflection increases, I shorten the string. Because a long string will make a stave bend differently to a short string, I focus mostly on the inner 1/2 to 2/3 at this stage.

Eventually the string gets so short that the bow starts to have a low, then increasing brace height. When the bow finally reaches full brace, I use the tiller string as a guide as to how long to make the proper string. Also, by this stage, the bow's pretty close to full draw too.

Actually, when I say that 'I' do those things I wrote above, I actually mean that it's what I have participants on my courses do. What I actually do, personally, is pretty much go from bandsaw to short string (with a reasonably low brace) straight to half draw or pretty close. Going from bandsaw to finished bow lately I've only been taking about an ounce off. But for beginners I wouldn't recommend that.



A bit of ephemera:

The tiller shape the bowyer is seeking should determine the thickness taper (or lack thereof). The width should be appropriate to the thickness to allow sufficient stiffness, and minimise set.

I've made pyramid bows that were quite highly reflexed right out of the handle, and they were rippers. And as for rectangular section, I don't think having a deflexed stave would preclude it. It'd just likely have a thicker section than another bow of the same specs without deflex.

[willie]

aussie

Eventually the string gets so short that the bow starts to have a low, then increasing brace height.

using your method for a say 50# bow, I could hang a 50# weight (temporarily, of course) on the short string and tiller the limb up to full draw, and at the same time be shortening the string so that it arrives at fullbrace about the same time the limbs arrive at full draw with the 50# weight?

willie

[Aussie Yeoman]

Not quite. Usually, once we get to full brace height, the draw weight is reached at about 10" draw measured from the back. I suppose I was exaggerating when I said the full draw was nearly done by the time full brace is reached. Mea culpa.

The bows we make are man-tall longbows.

[willie]

thanks aussie,
 no Mea culpa's necessary, just trying to understand better how to tiller before it's time to brace

willie

[Aussie Yeoman]

My advice would be:

* use the shortest long string you can
* never apply more force than desired draw weight
* get a short string on when tips deflect about 8"

[Andrew H]

For the program: How does one input nock position when gluing reflex into a backed bow?

For instance, if one were to attempt to glue in 2" of reflex using a form, but the bow only shows 1.5" of reflex out of the form prior to tillering, does one use the 2" number for the calculation or the 1.5" number?

[bushboy]

if you only got an 1-1/2" to start with <that's what ya got bro! !

[Mark Smeltzer]

So how would I use it for a static recurve and how do I account for sinew?

[Badger]

Sinew bows come in a bit lighter, just yes for backed bow and it will take off 10%, for the recurves just add how much the tips were behind the back of the bow when you started the bow, say 5" in the tip position column. I never really figured it with sinew but they tend to come out about liek a wood backed bow.