Probably a stupid tiller question

[Akbowman16]

I've been building for awhile and I always tiller my bows at 0 or, same for both limbs, or as close as I can. My question is: what is the reason for a 1/8th positive tiller or any positive tiller for that matter? But what I really don't know is where exactly do you take the measurement from? I would like to experiment with some different tiller measurements but I don't understand where to take my measurements and why? Any help would be appreciated.

[Bowjunkie]

The measurements are generally taken on the belly side of the limbs at the ends of the fadeouts or dips, and measured perpendicular to the string.

I don't tiller my bows to a predetermined positive measurement like most folks do, so I'll let them tell you why they do that.

I hold the bow and string on the tillering tree how it will be held when shot, and balance the limbs' relative strengths so the nock of the arrow comes straight back... being pulled neither one way or the other by a stronger limb... and then the braced profile is whatever it is, and it can vary from bow to bow... that's why I don't try to predetermine/guess it.

[Pat B]

I tiller limbs evenly but leave the lower limb slightly stiffer at full draw, no measurements.

[mikkekeswick]

It is simple mechanics - because the string is gripped above centre more 'leverage' is applied to the lower limb. Hence the need to make it stronger.
I've tried Bowjunkies methods and have to concure that it does work but my problem with it is that it isn't really necessary unless you are building radically different grips, with different pressure ponts etc for every bow.
Making the lower limb stiffer by about an 1/8th will normally get you very close. Then you adjust knocking point to find the 'sweet spot' where vibration is minimised.
The measurement is from the string to the riser fades or any equidistant pair of points on the limbs.

[monterey]

My last ASL build was, after final shaping and sanding, dead even at the fades as well as a few inches beyond.  Took it to the bale and shot it for a while.  It felt better and shot better than any others up to that point.  So, I left it that way.

The end recipient was equally happy, so I won't be messing with without shooting first!

[Mark R]

I take measurements equal distance from the center of grip to close as possible to fade out, mine are usually also center of bow tip to tip. I think the timing of the limbs is most important to a good shooting bow. Tiller can vary as to how you like to shoot and can be adjusted various ways.Since the bow string is pulled above the grip and if grip is center then the top limb is essentially shorter making it stronger,so if the weakest limb is the top then it evens it out a bit and hopefully times the limbs better. You can have a top or bottom limb longer or shorter but if there timed right it should in theory shoot well. Much to  play around with on the subject  with different bow designs.

[jsweka]

When I build a glass laminated longbow, I make the limbs equal length and dimensions, then upon first stringing I see which limb is a stiffer.  Even when both limbs are made the same, one will typically always be a little stiffer just do to slight imperfections in shaping or inconsistencies in core materials.  The limb that's a little stiffer is then the lower limb and I finish the bow, typically with little to no more tillering effort.

So I really don't tiller to a specific positive tiller.  It just happens.