Any advice on bottom limb tiller?

[bjansen]

Hello,

I am working on a 66in longbow and will perform the final tiller tonight.  The arrow shelf is 1.25 in above center and the riser is approximately 15 inches F2F.  

I know to tiller the limbs so that the bottom is stronger, but wanted to see if anyone had good advise as to how to check for that.  

What I have been doing is stinging the bow up and measuring the distance between the fadeout and the string (doing this for both the upper and lower limbs)and tillering to get the bottom limb measurment to be 1/2 shorter that that of the top.  Is that how others do this or is there a better way?

Also, does anyone know what the shooting symptoms will be of a bow which the bottom limb is not strong enoung....or even too strong?

I very much appreciate your help!

[DCM]

1/4" to 1/8" is more common.  Glass or selfbow?

With glass you may have difficulty tuning for your shooting style, which might contribute noise, handshock and extrodinarily high nock point.  Generally, the lower on the string you pull from, 3 under for example or even if you favor your ring finger on split draw, the less positive tiller you need.

On a selfbow if you put in too much positive, particularly if you handicap the upper limb by making it shorter w/ the arrow pass above center, it will have a tendancy to take more set over time.  One work around is to use more wood, by making it slightly wider.

It's a three bears deal, just right is just right.  But if you must err, err on the side of too much tiller and simply raise the nock point to take some of it back out.

What matters the most is that the bow equalize at full draw and not rotate, favoring either the upper or lower during the draw.  Unless you have a partner to help draw the bow by hand while you watch this "dynamic" tiller, replicating as closely as possible on the tillering tree is essential.  I usually use trial and error, where I get it close on the tree and then just shoot the bow and tweak it until I get the best results.

[bjansen]

Thank you for the response I appreciate it.

This is a glass laminated bow.  And actually, I have been keeping that tiller on my other bows 1/4 or even 1/8 like you said because I could just not believe that it had to be that much stronger to result in a 1/2 difference.  Another bower told me once to go 1/2 or 5/8 but I could never rationalize it.    

I do indeed shoot split, 2 under...i never tried 3 under and I understand what you mean by putting more pressure lower on the string and that effecting the tiller...it is something I never thought of.

What did you mean by rotate at full draw? (limb twist?)

What do you recomend for the arrow shelf...1.25 above center...more or less.  I am open to all suggestions, and again appreciate your great advice.

[DCM]

Glass bow is not critical.  I use 1" to 1 1/2".  Very commmon.  I've only made a couple from scratch, redone a couple more.  Lots of selfbows though and tend to put the arrow pass a little closer to center.

Not rotate at full draw, but on the way to full draw.  Sometimes the pressure point on the handle while drawing on the tree is different than by hand.  If when you draw the bow by hand you feel is rotate as your draw, too much positive tiller will tend to rotate lower limb toward you, you know you used too much tiller for your shooting style.

[bjansen]

Thank you again.  Great advice and I really appreciate it.  I will put that knowledge to work tonight.