positive tiller... How to?

[arachnid]

Hi Guys.
 
When tillering a symetricl bow, how do I know how much stiffer the bottom limb should be?
I've read that it needs to be slightly stiffer but how much is slightly? How do I mesure such a thing?

And, is there a difference between a straight limb bow and a reflex/deflex desigh (like a 3 pc takedown)?

I'll be graetfull for any info on the subject.

Thanks

Dor

[Pat B]

I never measure for positive tiller. On most selfbows you can only measure accurately at full draw, IMO. I just look at it and see if the bottom limb is slightly stiffer.

[huisme]

+1 Pat, most of mine are apparent at brace but those oddballs absolutely necessitate measuring/looking at full draw.

[arachnid]

How much is "slightly"?
How do I eyeball it? Does it need to bend evenly but less the upper? (Meaning the tip is a bit higher, when looking on the bow on the tillering tree)?

[huisme]

The gap between mid-limb and string should be just sliiiiiiiiiiiightly greater in the upper limb (take any character into account!)

[RBLusthaus]

I measure the greatest gap between belly and string  on each limb at brace.    Ideally, that place should be the same distance from center on each limb but I find it varies a little here and there.   I shoot for 1/8 positive tiller but seldom get it.  1/4 ish.  How does is shoot is a much better guide than some quirky measurement, though,  IMO.   Just use  measurement as a guide. 

[Pat B]

We are not talking about rocket science or brain surgery here. It is "primitive" archery. Slightly is a little less than too much but not as much as not enough. 

[bushboy]

Easy to do with a lam or board bow with straight tips.hold the back against a door frame and measure from frame to tip.rotate 180 and measure again. Oddly enough the set will also equal the pos tiller when unbraced if it's balanced.hard to do with recurve because they are rarely identical and will pull out a bit when worked.same for staves from. What I've seen so far.

[George Tsoukalas]

1/4" is fine. Have someone snap a digi pic or check in a mirror. A window at night works too. Jawge

[bubby]

We are not talking about rocket science or brain surgery here. It is "primitive" archery. Slightly is a little less than too much but not as much as not enough. 





I about spit out my drink, great answer Pat

[Springbuck]

Arachnid, unfortunately "slightly " is the right answer.  I'm sure every individual bow has a sweet spot, but it's going to vary with the archer and his grip, and the style of bow.  A shorty might look and feel very lopsided with 1/4" difference, while a long, long, longbow might want more.

Look at the Yumi design, and look at the archers hand. You can get away with a lot, obviously,  if you shoot it right.

What I keep in mind primarily is the strain on the wood.  If the lower limb is a tad shorter, it will act stiffer. I want to strain it that tiny bit less then, so that it doesn't take MORE set than the top limb.

[arachnid]

I guess thats where the "art" comes in to play... knowing that sweet spot.

[Springbuck]

Yeah, and I don't always find it, but that is why people go with rules of thumb.

How about this.   Imagine you had a bow that bent perfectly symetrically, with the hand's pressure point exactly in the middle, and the drawing hand directly behind that.  Now, the arrow has to pass above the hand, so it is an inch, plus, above the middle point.  This brings the string hand up a bit, too, so now the pressure points on handle and string don't line up, and the lower limb acts slightly weaker (string applies more leverage).

So, if you cut just enough off the lower limb to make the STRING even again, narrow and re-nock the lower tip, you'll be in the neighborhood.

[Sidewinder]

I guess I've never paid too much attention to measuring it. I try and make the bottom limb the slightly stiffer limb. I usually set out with the intention that a particular limb will be top and one bottom, but it does'nt always work out that way for one reason or another and I have to shift gears and swap top and bottom.
Thats also one of the reasons why I don't like cut in shelves. If I find the need for a shelf for someone to shoot off of I glue one on with built up leather. I have also found that if the bottom limb starts out stiffer, after its shot in pretty well it tends to balance out due to the fact there is more strain on the bottom limb. Danny

[bradsmith2010]

I try to make the bottom limb slightly stiffer,, just enough so I can see it at full draw,,
if the arrow is not flying right or the arrow is hitting my hand a bit,, I will make it stiffer until the bow shoots smooth,, that being said,, it the bow is shooting very smooth with good arrow flight,, I figure the tiller is good and I dont look at it any more