Should I really be concerned with 3 under tillering ?

[Stiks-n-Strings]

Well I discovered today that I think I like to shoot 3 under. my groupd improve quite a bit.

 Any way when I build a bow I usually build it with the bottom limb 1" to 1.5" shorter. I have always shot split finger.

 Do I really need to be concerned about tillering for three under when I build my next bow or will I fine just going like I'm going?

 Stiks

[b.glass]

Good question Stiks. I've been wondering somethign similar. I'm thinking you get the same bend profile on bows tillered with limbs that are the same length. And you build them with even limbs for three under shooting. Is that right?

[bjansen]

Thats how I do it B glass.  

There have been some past posts where some great theory has been shared on this question.  I think the best thing to do Stiks is take your bows out and shoot them 3 under....if they still shoot the way you want them, perfect.  If the bottom limb is recovering more quickly than the top, then start building them with less positive tiller...I try even tiller to slightly positive (1/16th positive tiller) for 3 under.

[Stiks-n-Strings]

Sounds good.
 
 I was out shooting with my youngest girl today and told her to try it cause I thought it might help her. I was shooting the character bow I just finished and tried it myself and it was putting them in there better than shooting split finger.

 Gonna try it with some other bows. I may have to start building them for three under.

[BigJim]

They say if you are building a self bow that it is important. It is more gimmick than necessity on laminated bows.

BigJIm

[4est trekker]

Chris, I shoot both 3 under and split finger.  I tiller all my bows with a slight positive tiller for 3 under and just a touch more positive tiller for split.  However, that doesn't matter near as much as raising your nock point and raising the brace height slightly when shooting three under.  That's made the most difference for me.  So, spend a little time tuning your bow, but don't worry much about tillering it for a particular finger orientation.  That said, I do adjust tiller for shooters who have a high or low wrist position in their bow hand.  That'll throw the tiller out of whack faster the three under/split finger.  

Best of luck!

[Roy from Pa]

I  sometimes think about tillering differences for split or three under, and it drives me crazy. Then I see guys post about tillering their bows on the tillering tree, and they are pulling from the center of the handle. Myself, I like to place the tillering pull rope about where the arrow nock will end up being on the bow string when you shoot it. Afterall, that is where we will grip the bow string when we pull it back to shoot. So all I can say is Stiks, I still don't know. LOL

[Osagetree]

Striving for tiller perfection is always good and shouldn't be discouraged, but,,,,

Regarding selfbows: Would primitive man be concerned with positive tiller? Does it matter at 15yrds? In my opinion, No, not enough to matter!
To me getting too technical takes the fun out of it. I do believe that each bow shoots differently. Finding each bows sweet spot w/brace, nock point, arrow spine and adjustments to shooting form is the fun part to me. Some I shoot 3 under, some not. Some I shoot with a heavey cant to the bow, some not.
Besides, I believe with humididty changes, winter to summer the wood expands and contracts to some degree, surley affecting your tiller & possibly string allignment if you've ever put any heat bend in the bow. And if not, the shoot in period of the bow will change things a bit which would mean some readjustment to tiller.

I know hand shock is an indicator, but how the heck else can you tell one limb is recovering quicker than the other? Slow motion video?

Regards,,, It's early before work and I probably should have kept my mouth shut as I never get into these technical discussions.

[canopyboy]

Ok, so can I ask a basic newbie question here?  Which direction is "positive" tiller?

To the last post, one of the reasons I'm finding self bows so addicting is that not knowing what you guys are talking about, I was still able to make something that shoots well (even if a bit light.)

[Stiks-n-Strings]

Joe,

 I ain't gonna lie, I kinda feel the same way. LOL

 I think I will tiller till they look and shoot good and leave it at that.


 Canopyboy positive tiller is when the lower limb is atouch stiffer than the top and will be indicated in measuring from the string to the limb a little past the fade. For example the top limb would measure say 6.25 from string to limb and the lower would measure 6 giving you .25 positive tiller. (At least I think that's right)

 Stiks

[Steve B.]

When I was placing a shelf on a recent self bow I experimented with location in the same way I would with nock point height during arrow tuning.  I put the shelf dead center on the handle, shot it, then moved the shelf up in half inch increments and reshot to note any differences in performance.  I also flipped the bow upside down and did the same.
There was very little, if any, noticeable difference in actual shooting even though tiller may be noticeably changing with the varying changes of pressure points from moving the bow hand up and down.

Also, I shoot split finger and tiller by actually pulling the bow by hand and using a mirror to note limb affect because hand placement and pressure affects tiller.
Try it sometime...then flip the bow upside down and note the tiller change.  The positive tiller, for example, may not stay with the top limb as it is flipped, it may move to the new top limb.

[DCM]

;-)

I'm one of those guys where the techincal stuff puts the fun into my hobby.  On the other hand, I've found no substitute for trial and error, just shooting the bow during the final tillering and finesse stage.  While potentially not as important for glass bows, where there's gobs of extra work capacity in the material, getting the tiller to match the archer as close as possible pays dividends in performance, handshock and quietness.

That said, there's no harm in understanding the fundmentals of how a bow works, as if you are in it for the process, moreso than the product, there's always something to learn, or see differently.  Another way to say, I've never built a bow that I didn't think I could build the next one better.

If your arrow pass is 1" to 1.5" above dimensional center, the upper limb is shorter, unless your handle is shorter than 3" total.  The arrow doesn't know the "extra" lenght is the handle, versus the bending portion of the limb, from the geomtry and physics pov.  Fold your bowstring together at the nock point and note the longer string segment.  That's what the arrow sees at the start of the power stroke, a long segment (lower) on a long stiff spring, and a short segment on a short weak spring.  The more asymetry, the more positive tiller you need... bearing in mind nock point is just a proxy for where you draw the bow, so drawing three under is counter intuitive, as it frequently take a higher nock point but actually induces less asymentry, by the drawing force being lower on the string, thus less tiller.

I don't actually know what I'm talking about, I just type this stuff to read challenges to it, which I welcome, to help either strenghten, or test my understanding of it.

[canopyboy]

Ok, this is starting to make a little more sense to me.  At least the positive tiller and why you'd have some.

But now the engineer in me is trying to run through the dynamics of this 3 under vs split thing.  Yes, when you are pulling back and when you are at anchor, the difference can affect your effective center of pull.  Three under brings you closer to symmetric assuming the same distribution across the fingers.  But once you release, the center of force quickly transitions to the arrow nock.  So for the majority of the arrow's acceleration, the tiller is really controlled only by the arrow and the two different release methods shouldn't make a difference.  No?

[DCM]

I like the engineer in you.  I've chased that bunny trail a bunch, mostly in the context of nock travel, up and down, and the interlationship with limb/string lenght and static tiller.  Seems like the more asymetry, the more tiller, the more nock travel.  At one time "negative" tiller was suggested as appropriate for the typical arrow pass above center construct, and I thought effect of nock travel would negate it's use, even though it seemed plausible in terms of balancing the strain on the upper limb, relative the lower which gets a free ride on two accounts, being stiffer and longer.

On the three under question, maybe because it gets more "free travel" before the lower limb "sees" the arrow?

This stuff breaks my brain everytime I entertain it.  To be so "simple" traditioal bows are maddening complex to model, imho.

[b.glass]

You guys are giving me a headache!      :p  

So when John Scifres shows us a picture with the two limbs of a bow transposed, he is NOT tillering for a positive tiller?

[003sim]

How was the bow tillered that you noticed the improved groups? This may answer your question for you. I would just go with that because it worked.  
  The other route is to build a bow like the one mentioned above with the other tiller in question. Then keep the one you shoot better with and give the other away as a present.

[Stiks-n-Strings]

I can shoot this bow either split or three under, I just noticed a little better groups with three under.

 It's tillered with lower limb a tad stiffer and the lower limb is 1.5" shorter than the upper limb.

 I'm like Bona this stuff is giving me a headache LOL. I like simple answers and like to just keep it simple but that's just my flavor. All the technical guys are needed though or we would not be where we are today in this fine craft.

 Stiks

[walkabout]

i cant remember where i read it but i read that you should make the top limb longer for three under shooting anyway, as it puts more of the force on the lower limb.

[Osagetree]

Yep,,,    

Yea B.Glass,,, wonder if John will chime in on the subject?

[Stiks-n-Strings]

Looks like I opened a big ol' can of worms Joe