Positive Upper Limb Tiller?

[GaryL]

Hey there Everyone,

 I just started out learning how to make bows, in fact I am just about to start my second Board Bow and I have a question about tillering.

Somewhere along the line I read somewhere that your upper limb should have about 1/8" more positive tiller than your lower limb assuming that you are building an A-symmetrical bow.

The first bow I build looked pretty good as far as the the limbs bending evenly ,however; the limbs, when measured, appeared to have the same amount of tiller.  I went ahead and tried to correct this by removing material from the belly of my upper limb and thats when things went south, should have just left it.

My question is, how important is this, especially for a new learner?

Should I just focus for now on even limb arc or is positive upper limb tiller imperative? 

I have read several books on self bow building and I have not seen this mentioned but with regards to my ASL's this seems to be a pretty important factor.

Thanks in advance for any advice.

[Del the cat]

I used to think it was hogwash, then I made and Ash flat bow, the tiller was fine, I'd shot a load of arrows through it and then suddenly the lower limb went weak... it looked awful. If I didn't know better I'd say it had been over drawn, overstrained during stringing or run over by a car! It had never been out of my sight, and I recovered it with heat treating and re-tillering, but it had lost a good few pounds.
Having that lower limb a tad stiffer can stop that happening. IMO it's vital to support the bow on the tiller as it will be held in the hand and to pull it from where it will be drawn. In fact I s'pose it's an argument for drawing it up by hand in front of a big mirror (but then it's hard to measure the draw weight)
Del
PS. This post from my blog may help (or confuse  )
https://bowyersdiary.blogspot.com/2013/03/tillering-symmetry.html

[Eric Krewson]

I shoot split finger and start the final tiller with both limbs equal. I usually get some arrow hop with my shooting style and even tillering. I will remove upper limb material until the the arrow flies true and the hand shock drops to almost nothing. I almost always end up with 1/8" positive or slightly more on the top limb.

If you shoot three under you will probably be happy with even limb tillering.

[Bayou Ben]

I do like Del and support the bow exactly how I intend to hold and pull the bow.  Positive or negative doesn't matter one bit to me as long as the bow is balanced in the hand when I'm shooting it.  Way too many variables to always go for an arbitrary 1/8" positive tiller IMO (although sometimes 1/8"+ tiller is what the bow needs).   
Taking a picture or looking at the bow in a mirror while you draw it would be a better approach.  If it leans to one side, that side is stronger and you can take a few scrapes off of that limb until it's balanced....take a look at this discussion
http://www.primitivearcher.com/smf/index.php?topic=62531.0

[Bryce]

My positive tiller depends on how much longer my top limb is.
My top limb on a longbow is an inch longer, so 1/4” positive is appropriate
If the top limb for some odd reason was 1/2” longer than it would be 1/8” positive. And so on.

[George Tsoukalas]

I like the lower limb slightly stiffer at full draw. I tiller from the center to about an inch before full draw and then finish tillering with a digital camera. I have a family member take a shot at full draw.

A mirror or a window at night gives a nice dull draw view also.

Jawge

[Perkinator]

Negative tiller looks really wrong to me, but the best bow I ever shot with had much weaker bottom limb. I flipped it upside down, but it didn't shoot *quite* as well. Then I accidentally dropped it into a lake... 

[Ryan Jacob]

Perkinator
It didn’t float back to the surface?

[Badger]

   I find positive tiller usually works best for me. My arrow pass is usually about 1 1/4" above center. I don't tiller a bow to how it looks in the hand at full draw. We let go of the string when we shoot an arrow and a fulcrum no longer exists. I want the arrow to draw straight back from the shelf with the support right below the arrow rest. When I shoot the bow I knock the arrow about 1/4" or less high. I think your best knocking point falling into the 1/4" or less range tells you how well your tiller is balanced.

[bradsmith2010]

yep

[Jim Davis]

... . I have a family member take a shot at full draw.

A mirror or a window at night gives a nice dull draw view also.

Jawge

Jawge, I've seen some of those photos, and not one has been dull!