Primitive Archer
Main Discussion Area => Bows => Topic started by: Taxus brevifolia on December 14, 2018, 04:13:16 pm
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This is for a yew selfbow, 59.25" ntn, target weight 43lbs at 24". Currently 43lbs at 23"
To get where I'm at now, when I got it to full brace I very carefully tillered both limbs bending exactly the same. Measurements checked, meticulously. Penciled the outline, flipped it over and nearly a perfect match. Eventually it was a perfect match. Then bringing it out an inch at a time, and it's introduced (negative?) tiller of ⅛" ... The string at lower midlimb is ⅛" higher than upper midlimb.
I think sometimes people intentionally fix it to have a positive tiller, so I'm asking what should I do here, and am I using the correct terms, is it positive tiller when the upper limb bends more? I think I've got enough room here to fix it anyway I like in this regard.
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"is it positive tiller when the upper limb bends more?" Yes
Can you turn it upside down?
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A few even scrapes on the upper limb (belly, or narrow the sides) and it should correct it and bring the the draw back that final inch.
May be best to shoot some arrows through it tho' .
Seeing it on the tiller would help.
I've had similar on the Yew bow I'm working on (I did a couple of short vids).... it was awful, I corrected it and got it looking good at about 24" (first video) then just eased off the outer 1/3 when I fit the nocks and brought the outers round.(second vid)
(It's a rather philosophical, and irrelevant point, but did drawing it further induce the slight missmatch, or was it simply not visible until you got to a longer draw? ::))
https://www.youtube.com/watch?v=kWaO9K4yko8&t=28s (https://www.youtube.com/watch?v=kWaO9K4yko8&t=28s)
https://www.youtube.com/watch?v=gYwckQDlBE8&t=7s (https://www.youtube.com/watch?v=gYwckQDlBE8&t=7s)
Del
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Keep in mind, taxus, that in the final analysis nothing approximates how you hold the bow and draw.
So you can draw in front of a window at night, a mirror or have someone snap a digi to evaluate tiller. Then ease it gently into the last inch.
Once I string the stave I no longer use aggressive wood removal tools so I use scraper-like tools. That means there is not much finishing left. As I get to an inch below draw length, I look to have draw eight at that length. That leaves me enough room for final sanding after full draw is achieved.
Jawge
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Generally at that close to ultimate full draw and everything looks good the last inch shouldn't be more than a few scrapes on each limb to reduce the weight. Have someone take a pic of you drawing the bow to full draw. The static bend on the tree can be different than the dynamic draw in your hand. Your hand helps to compensate for any unevenness.
At this point I'd go out and shoot a couple dozen shots then check tiller again.
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As the others stated, it’s best to get your last couple few inches by drawing the bow in hand.
Use a mirror, or get someone to snap a FD shot. I like to film myself and take screen shots. Tillering only a tree will often make your top limb a little stiff, some variables change when you draw by hand,
and it allows you to FEEL the limb balance, not just see it.
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Thank you gentlemen!
I've been using only a cabinet scraper since I got it braced.
I've been fine tuning it with a tillering gizmo, it shows me discrepancy I simply cannot see with my eyes alone. To use it I have to lock it in draw.
I need to know if I should give it slightly more bend in one limb? I know people sonetimes do.
The upper limb is ½" shorter than the lower
Because I put the nocks 1" from the upper tip and ½" from the bottom tip
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Can you flip the bow? To make the arrow lift nicely from your hand the lower limb should be quicker than the top limb. You achieve this either by a longer top limb or with a stronger lower limb. I usually combine those two effects.
If your top limb is shorter it would be best to flip the bow if string alignement allows. If you dont flip it, you will have to make a much weaker top limb.
You can check balance of the bow: If the arrows constantly group low / If the arrows scratch your bowhand and hurt => top limb is too strong...
Imho
Cheers
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Shoot it first then come back and check tiller again. Pics would really help us.
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There's nothing at all wrong with a negative tiller if that's what results from balancing a bow's limb strengths relative to your holds on bow and string. Balanced is as balanced does.
A bow's side profile at brace, i.e. tiller, should not be predetermined because some bows will be balanced with a positive tiller, some even, some negative. A tiller measurement should be an afterthought, or postscript... a final result of our balancing efforts during tillering. A bow that 'lifts the arrow off your hand at the shot' is not balanced and it's inflicting porpoising into the arrow's flight. My bows are balanced, the arrow flies straight away, and clears my hand just fine. Don't flip it or weaken the top limb simply because you've been taught to be biased toward even and negative tiller. You may be making a lesser bow if you do.
I say, if you don't have your tillering tree set up to adequately mimic your fulcrums on bow and string, then you should draw it, learn to feel how it acts during the draw, and take pictures from both sides to study. It should not lean forward or back any noticeable amount. Weaken a limb if it pulls its end of the handle toward you until it's balanced at full draw. Then shoot it.
By the way, the limbs don't have to be a perfect mirror image of one another, and often they absolutely should not be.
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I'm learning so much from you guys!
Seriously, thanks