tillering 3 under vs. split

[bjansen]

Hello all,

I was wondering if you guys could help me figure this out.  I previously shot split and previously built my bows with positive tiller (the bottom limb stonger by 1/8 of an inch at the fade out).  When I would tiller the bow in this manner, I would put it on the static tiller stick and ensure the string was right in the middle when drawn on the stick. Then check to see how the limbs were bending.  

I have been shooting 3 under and am making a new glass bow (which i want to tiller to 3 under).  I currently have it just like i said above (1/8 stronger at the bottom measured at the fade out).


I am wondering if I should have more or less positive tiller than if I was making a bow split. I am guessing less positive tiller...I saw Hera's build along and he makes both sides even for 3 under...

Second question...when I put the bow up on my tillering stick and draw it down to check how the limbs are bending...should i put the string off center as if I was pulling it 3 under...or keep the string centered on the tiller stick.

Thanks guys!

[bjansen]

Other info that may help with this question..not sure...but here it is

this is a 68" NTN mild R/D longbow, 16 inch riser...build along is coming soon when i figure out how to tiller thing

[SoNevada Archer]

Brad
I shoot three under too. Byron Ferguson suggests for 3 under shooters, that the bottom limb be a 1/4" strong or less. So if your at 1/8" sound like your right in the ball park.

I have built 2 bow's with about 1/8" heavy bottom limb because of Byron's suggestion. I shot one and my son shots the other, we both like how the bow's shot.

But honestly, I have tried to visualize how the limbs are bending...I don't really see how being 3 under makes for a less heavy lower limb being right. It seems to me that 3 under shooters are putting more strain on the lower limb, therefore I would think the lower limb should be heavier to compensate for the extra work it's doing...but I guess thats not how it works!  :rolleyes:

[bjansen]

Thanks for the input...I was thinking the same thing you were.  You had a great TD build along by the way...I am workin on a TD right now.

Thanks

[DCM]

You want to try to draw the bow on the tree, or stick, as closely to how you will draw it by hand, in terms of placement of the stick on the bow and string.

By drawing the bow closer to the center of the string, using the 3 under style, you mitigate the asymetry inherent in having to draw a bow string at a point higher (toward the upper limb) than the pressure on the bow itself.  This inherent asym tend to make the bow want to rotate, upper limb toward the archer.  Positive tiller has the purpose to offset this.  Since 3 under offsets the effect as well, as does placeing the arrow pass closer to center, then less positive tiller is "required."

Ideally one should shoot his bow, quite a bit, and adjust the tiller with trial and error until he get's optimum performance.  I generally start at 3/16" and work my way down which is appropriate for me.  On selfbows this is fairly simple and natural part of the process.  Less so on glass bows, so perhaps only one or two cycles of trial and error, staying within the know territory for your design (most frequently 1/4" to 1/8" positive, or 1/8" to 0 for three under).

[bjansen]

Thanks for the advice DCM.  I greatly appreciate it!

[Art B]

Hey David, I've had to re-think this whole " pull on the tree as you would by hand" thingy. The concept of even bend, even strain from floor tillering to full draw is broken by mimicking ones draw on the tillering tree. Only way to keep even strain on the limbs is to draw the bow dead center on the tree. Then, once the bow is drawn by hand, the bow hand becomes the equalizer by counter heel pressure. Probably not worth even .02 but there it is    . -Art B

[DCM]

Art,

I admire your contribution, and skill, so your $ .02 has a pretty fair "present value" in today's market.  LOL  I'd like to hear more about your thoughts on how drawing on the tree differs from drawing by hand.  I think it mostly involves the placement of the draw hook on the string.  And the fact is really not practical to have much offset on stick or tree, due to the rotation phenomenon I mentioned.  While I advocate it, predominantly because most bowyers seem to make their trees with a "cradle" versus a single point of contact and thus it works.

I on the other hand use the single point of contact.  As such I can't really offset the draw hook much, or the bow will rotate off the tree if I don't have the tiller pretty close. I tend to place arrow pass closer to center, which help mitigate the need to offset of the draw hook as well.  And I start shooting by hand early in the process (about 4" to 6" before full draw) to help compensate as well.  

I think when folks have bows pull out of till from shooting, and some would advocate to turn their bow upper limb into lower, they've suffered from having built a bow best suited to the tiller tree's shooting style, versus the archer's.

All,

While my use of language may sound authoritative and convincing, I'd encourage you to regard my comments with the same skepticism as any other novice.  My purpose is to have you consider the alternatives and ideas, rather than accpect my ideas.  I've learned from experience, nothing beats one's own personal direct experience, in particular comments from others'.

[Art B]

Often, the bow hand and it's ability to effect tiller, is overlooked. As you mentioned, and I agree, that getting ones bow to even brace and proceeding from there by hand to full draw produces the desired results. Faily easy to balance the drawing hand against the bow hand to apply equal strain to each limb this way. So sticking with the notion that applying even stress to the bow's limbs from floor tiller to final tiller hasn't changed. So when we go to drawing a bow on the tillering tree this concept shouldn't change either. Only way to achieve that is to draw the bow from dead center. No way that I know that you subtitute the bracing effect of the bow hand on the tillering tree. So there's no way really to mimic ones grip and draw on the tillering tree. Best to keep even strain on the limbs by pulling straight down, dead center of the bow. Then, when the bow is hand drawn, you're mimicking exactly (by keeping equal strain on each limb) what was done on the tree by the drawing and bracing bow hand. In mind mind as least, we had it backward.-ART B

[DCM]

I see your point Art, I think.  Folks naturally adjust the hand pressure to keep things "even."  But while I concede it is difficult, perhaps not even practical, it is desirable to "try" to simulate one's own body mechanics when working a bow on the tree.  At the same time, I don't even advocate "working" a bow on the tree per se, rather prefer actual shooting by hand, reserving the tree for more preliminary work.

[Art B]

But while I concede it is difficult, perhaps not even practical, it is desirable to "try" to simulate one's own body mechanics when working a bow on the tree.

With a "close to arrow pass" as you use David you will not notice a lot of difference (but still some) with your method. It can be helpful in maintaining a positive tiller throughout the tillering process because it works the upper limb more than the lower. But when you get into the arrow pass range (1 1/2"-2" from center) that I prefer then this proceedure works the upper limb too much. I believe that this is where folks are beginning to think that adding more strength (negitive tiller) to the upper limb is a good idea.