Someone splain this to me please

[VFT]

OK, here's my question. Take it easy on me now for I'm a little slow.

Why is it my nock point is not centered (on a 2 cam) between the axles? I would think, if both cams are in time, the string would want to pull from the exact center of the string. I can understand a single cam could be of center, but shouldn't a 2 cams nock point be centered? If not, why not?

It's off center by 16.5 from the top and 18" from the bottom. :( If I tried to center it the arrow would just about ride the arrow shelf.

Or could this just be it is wrong and I need to center it? :)

Or you don't know what I'm talkin about. :D

Thank you's all.

[Tejas Raz]

That's actually a very good question Bill and one that needs a good public answer.

But I'll let the real Pro's answer it! :D

[ldfalks]

What kind of bow are you shooting?

It's not necessary to have a centered nocking point to have level nock travel as long as the string unwinds evenly from both cams.

Pearson has gone to a centered grip which puts the nocking point 1.5" high of center. Looks funny but the bow holds much better because the balance is improved.

I likes it like that... :D

[imanut2]

Bellows...I know exactly what you mean...and it makes perfect sense...

....but, I'm a single cam person....so my question is....are the cams identical? Same exact size, shape, etc? Limbs exactly the same size? I'm just wondering if maybe one of the cams or limbs is slightly different to account for this...although I'm guessing they are exactly the same...but like Isaid...I prefer single cams :D

If the shelf is in the center...then obviously, the nocking point is off-center because the rest is raising it off center....shoot off the shelf and you'll be fine :D

Good question, though....

[Tejas Raz]

This would be a great place for Edgell Terry to jump in and answer with his designer/engineer background!

Londa? ET around? :D

[TexHunter]

If ETs not around I would bet Javi or WR could 'splain!

[rock monkey]

the geometric center of a riser isnt the berger hole, but the throat of the grip. its done this way to balance the riser and the feel of the bow.

some companies do get the geometry of the bow to shoot in the geometric center of the string, some dont. it really depends on the layout of the bow itself.

just for s&g's, i measured my system and my 27 year old split t and neither one are geometrically centered.

[VFT]

What kind of bow are you shooting?

It's not necessary to have a centered nocking point to have level nock travel as long as the string unwinds evenly from both cams.

Pearson has gone to a centered grip which puts the nocking point 1.5" high of center. Looks funny but the bow holds much better because the balance is improved.

I likes it like that... :D


I kinda understand, but :D If your not pulling from the center, isn't one cam rotating faster then the other to make up the difference?

The bow are an 05 allegiance and an 06 Bullet-x, they are both high.

[DUBBYA ARE]

Can't wait to see what Javi and Edgell & Londa have to say about this :eusa_think:

I'm with rock monkey on the center of most bows being at the pressure point of the grip.......I'd think it would be hard to design an inline grip with the center of the string :eusa_doh:
Why do we tiller tune and advance the upper cam? or add more pounds to the upper limb?

[Javelina]

If you measure around the two cams you will find that the distance each travels during the draw cycle isn't the same... This is done to compensate for the nock being high...

[VFT]

If you measure around the two cams you will find that the distance each travels during the draw cycle isn't the same... This is done to compensate for the nock being high...


Thanks Javi and everyone else for the replies.

[lterry]

Bellows1 ...here is ET's reply to your question:

First of all when you time a 2 cam bow...you time it at full draw. That is, each split cable, upper and lower has to hit the draw stop on each cam at the same time at full draw. Here's why you have to do that. Lets say you put the arrow nok center on the string, you can do that...but...what you can't do is shoot the arrow off of the string at a 90 degree angle. Why? because to do so you would have to shoot it right through your hand. I think you get the picture by now.

So here's what makes it work. By timing the cams at full draw, the top limb is not flexing or bending as much as the lower limb, this allows the upper cam to rotate a little faster and feed off the bow string a little faster. By feeding faster it is wrapping the lower harness around the mod on the upper cam. Thats making the lower cam rotate faster, because it is 18" from the point of pull and the top is 16.5" from the point of pull. So by feeding faster it makes each cam reach the dead stops at the same time.

In timing a two cam at full draw, you are really lying to the bow...you are making it believe that the point of the noc set is in the center of the axles. This puts equal forward energy when shot to the cent line of the arrow shaft...also allowing each cam to hit bottom at the same time....taking away that big ugly shock.

By the way, when shot the arrow leaves the string in the first 8-10 inches of the forward travel of the string. So when tuning a two cam, remember after you set the nocking point and then time your bow, it will cause your nocking point to go high or low, depending on which cable you twist up. To do it right you will have to keep moving your nocking point to center and then recheck your timing over and over until both are insink.

Let me warn you, if you have never done this you may be in for a real nightmare. You'll need a bow puller and a bow press to do it right. I hope I've answered your questions in a way all can understand. If not let me know. :D

ET
Storm Archery

[DUBBYA ARE]

Looks like a good one for Tips & Tricks + Reference area ........ Thanks ET & Londa.

[Tejas Raz]

Looks like a good one for Tips & Tricks + Reference area ........ Thanks ET & Londa.


Exactly what I though when I first started following it Wes! Now's a good time to move it, though we can still add to it if anyone wants to.

[Oldaro]

Let me just add that the nock and rest keep the arrow at the center of the bow function, whatever the actual construction. The proof is in what Javi said; the length of the string unwound from each side ensures that the arrow expelling force equals out at the nockpoint.

:D

That, to me, seems much easier to understand and probably to construct than, for instance, the kyodo bow, where the arrow position is practically dividing the bow into upper 2/3rds and a lower 1/3rd!

I imagine it originated in the past with using the plain bamboo stalk to make a bow. Since the lower, older part of the stalk is thicker and harder to bend, they simply moved the gripping point down the length of the bow to find the place where both, upper and lower parts resist the draw about the same. Later on, the constructed bows copied the experience (tradition?) while shortening the bow somewhat, and bringing more power and drawing smoothness into the construct.

[VFT]

Thank you all for your help.

That does help clear up a few things. :)

[steelhat]

OK... this subject has gotten me to be a first time poster at Archerysite.net....

1. Do you mean to say that on any of my two-cam bows (not hybrid) bows, the cams are actually different at some tiny level? They sure look the same to me.

2. The previous posts also suggest that Tiller never equals zero on a tuned bow, or that the limbs of these mass-produced bows are actually slightly different?

Thanks for your experience and knowledge base!

Steelhat:5bowtie:

[TexHunter]

Good to see you post steelhat. Jump on in.

[Dusty Britches]

OK... this subject has gotten me to be a first time poster at Archerysite.net....

1. Do you mean to say that on any of my two-cam bows (not hybrid) bows, the cams are actually different at some tiny level? They sure look the same to me.

2. The previous posts also suggest that Tiller never equals zero on a tuned bow, or that the limbs of these mass-produced bows are actually slightly different?

Thanks for your experience and knowledge base!

Steelhat:5bowtie:


Let me be the first to answer your questions incorrectly! :D

1. No. the Cams on a 2 cam bow are different and travel at different rotational speeds.

2. Tiller can equal zero on a tuned bow.