Bow Physics revisited.....Bow Finished!

[EwokArcher]

I'm pretty sure yumis were for horse back archery correct? I may be missing the mark but that is a good example mark. When I was about 16 I tried to make an osage Yumi. 76 inches long about an inch wide more hand shock than a jack hammer lol I think I missed the whole limb timing weight distribution thing on that one.

[stickmonkey]

Jim Thorne Has conducted a lot of experiments in relation to grip position to  center or below centerline of the bow. Jim found for split finger being slightly below center preformed best and for 3 under having the center of the grip on the center of the riser worked well. Keep in mind too that Jim like most of us also dynamic tillers the limbs no mater the position of the grip. Having the limbs balanced and timed at draw is more important than grip position IMHO.

[joebuck]

Jim wrote

I suggest that you build your bows as symmetrical as possible coming off the form, tiller them as a perfectly balanced bow out to about 20″ draw (pushing at center and pulling at center), then adjust the bow pivot position and string pulling position to match the intended shooter, and then finish tillering the bow out to full draw so the tips pull to the same distance. I think you’ll find that sliding the bow pivot up or down during the tillering process will result in a more balanced bow and limbs that are closer together in strength. What you end up is essentially a bow with equal length limbs and an asymmetrical riser. It works for compound and target bow manufacturers

Wow!!!!!!!  Jim's webpage answered all my questions..........i hope he is right 

[joebuck]

Am i reading this right.....he says in this example....right side is upper limb. Last sentence says that making lower limb ( left limb) stronger would even tiller this bow out?  seems backwards

 

[joebuck]

Now this scenario seems exactly what i was asking...

[stickmonkey]

Am i reading this right.....he says in this example....right side is upper limb. Last sentence says that making lower limb ( left limb) stronger would even tiller this bow out?  seems backwards

 

Yes that is correct.  More stress is placed on the lower limb as you move your hand down down the riser so keeping the left side 1/8" positive will aid it. A single point string drawing will not put the same forces on the string as the hand does however it does well enough that unless you want to go through the trouble to make a griping device that will mimic the pressures the fingers apply a little better. I made one a few years ago and still use it but again the gains from using it are very small. That said I am of the mindset of adding up all the little small performance eeks will eventually show bigger gains. I do those thing strictly for my own OCD.

[stickmonkey]

Now this scenario seems exactly what i was asking...

No surprise here. Its an asymmetrical design with both the grip and pull point being 1" Below the center of the string and bow. I am understanding that your asking about tilling to a crawl which is above the center by a few inches. The thing is you dont know the crawl till you tiller and shoot the bow so in the end its just a guess on tillering but if you dynamic tiller as we have suggested based on the drawing method it may help you make the bow quieter. in the end it may just be a wash on whats gained vs longevity of the bow.

[joebuck]

Not really,   i place my hand on string for crawl exactly same place i have always for three under.  what i did move was the arrow up to under my eye   ...

I use to shoot 3 under with arrow right under my eye.......just never felt i had a solid anchor......moving to the crawl and placing my index in corner of my mouth while keeping the arrow still under my eye.............has been Awesome

[stickmonkey]

So If I have two bows you are saying you will put your hand on the same place for both on your crawl? If that is so then your Crawl is not accurate unless both bows and the arrows are the exact same. If you build a new bow or tiller the limbs you have on an existing bow the limbs will lose poundage which will translate to a small loss of FPS. 

How high above the normal nocking point on the string is your new nocking point/Crawl?

[joebuck]

Not sure SM if i understand your question.......but my project is for my new bow i am building...havent built one in 5 years and/or since i have changed shooting styles. ..........i shot for 20 years high wrist and split instinctive..  The last 10 i have basically shot three under and sighted down arrow like a shotgun.........

Crawl "tick" bit me months ago and have decided to build a new bow and go to thinking about tiller and set up....my style has changed to low wrist, three under and dam carbon arrows!!  ...........

the bow i am currently shooting i made 15 years ago and adjusted 10 years ago to even tiller....i moved string knock up to accommodate crawl  and not really really shooting bullet holes in paper...I love the crawl setup so got to thinking......i want to set up my new bow to be a tack driver shooting the crawl technique

[joebuck]

I moved knock up about 1.25"....my arrow is right under my eye and my index is in corner of my mouth

Jim Thorne Fig. 11 and explanation is Exactly how my bow is set up now.

[stickmonkey]

Not sure SM if i understand your question.......but my project is for my new bow i am building...havent built one in 5 years and/or since i have changed shooting styles. ..........i shot for 20 years high wrist and split instinctive..  The last 10 i have basically shot three under and sighted down arrow like a shotgun.........

Crawl "tick" bit me months ago and have decided to build a new bow and go to thinking about tiller and set up....my style has changed to low wrist, three under and dam carbon arrows!!  ...........

the bow i am currently shooting i made 15 years ago and adjusted 10 years ago to even tiller....i moved string knock up to accommodate crawl  and not really really shooting bullet holes in paper...I love the crawl setup so got to thinking......i want to set up my new bow to be a tack driver shooting the crawl technique

When you say crawl I think of a fixed crawl but that is a mistake on my end as you are not fixed?

I have been building all my bows for three under with even tiller and even center on the riser , center shot and using carbon arrows , micro dia  ta boot finding its quieter than tillered for split. Both are tillered in the same way Jim said so they are balanced at draw and timed to the gripping pressure on the riser.

[stickmonkey]

I moved knock up about 1.25"....my arrow is right under my eye and my index is in corner of my mouth

Jim Thorne Fig. 11 and explanation is Exactly how my bow is set up now.

In Jims fig 11 BOTH the grip center and string nocking point have been move down, not up. If you reverse that and move them both up then the top limb will need a little more strength to it to time correctly

[joebuck]

Figure 11 , the grip and where he grabs the "String" have been moved down....my arrow is above where he grabs the string...so fine tuning will probably include the arrow shaft  since there is a slight download pressure on the string stroke to the nock

[Bvas]

Am i reading this right.....he says in this example....right side is upper limb. Last sentence says that making lower limb ( left limb) stronger would even tiller this bow out?  seems backwards

 

The right limb is not bending more. The bow is tipping in the cradle towards the stronger limb.

[joebuck]

It appears that but......he used just a heavy parallel ( no riser) to better show the effects of his experiment

[TradBowyer]

My take is you have to separate glass bows and self bows. They are two different animals. Self bows are more critical of tillering and hand placement than glass bows are. For my glass bows I compromise by measuring center of the riser and routing out my hand placement under that point which puts my arrow a little above center. This is the best of all worlds for me. For selfbows I don't mess with fixed crawl or string walking. Most of mine end up being point on around 22-25 yards shooting 3 under anyway. And keep in mind bowlers have to make a bow to fit the masses. People complain now about prices can you imagine what they would cost if each bow was perfectly matched and tillered to each buyer? Lol

[Bowjunkie]

Matching bows to archers' idioms isn't too difficult. I tiller selfbows, backed bows, glass bows, character bows, bows with one straight limb and one reflexed limb, all of em... all the same way, they're all dynamically balanced, and I expect the first arrow from each of them to shoot wonderfully. Truly dynamically balanced bows are inherently tuned... all you should have to worry about is arrow spine.

Bvas is absolutely correct. His bow/heavy parallel is tipping on the tree. Compare just the 'handle area' of both pics. It's tipping, I promise. Ya gotta be super careful and understanding of this, or your assessments surrounding dynamic balance will be wrong, usually completely converse of the truth, and any following efforts, misdirected.

If a bow on the tree is allowed to tip without resistance, the STRONGER limb(relative to the shooter's holds) will come down farther... and the hook on the string(string hand fulcrum) will generally always follow a plumb line straight down the wall. The key to this method is to adjust relative limb strength so that the bow isn't tipping at full draw.

On the other hand, if a bow on the tree is clamped or otherwise held so that the handle area stays level, the WEAKER limb will come down farther(relatively speaking again), and the string hand fulcrum will drift off of the plumb line, toward the stronger limb. The key with this method is to adjust relative limb strength so the hook follows the plumb line.

So long as this is understood, either method will work to dynamically balance a bow, assuming all else is properly set up... i.e. you are in fact holding and pulling from the proper places... as the archer will.

[hightop_hunter]

I was just getting on here to Add a question about moving the shelf/center of the bow up or down, and why it matters but its like the forum read my mind. thanks for all the useful information. I'm sure I will have to reread this post a few times but im still not sure I understand why you move the shelf up 1"  if the limbs are timed properly  wouldn't that change the timing of the limbs if you are no longer anchoring in the dead centre of the bow?

[Roy from Pa]

No, you define the arrow shelf and grip first, then place the trees pull rope where the middle finger of your drawing hand will be when shooting the bow and time the limbs to that..