Measuring centerline of arrow vs. centerline of bow

[McDave]

I've never felt comfortable lining up my eye with the string centered on the limbs, and then trying to see if the arrow shaft is inside or outside of the centerline of the bow.  It just seems like too much to line up all at once, and a tiny movement will make the end of the arrow shaft appear to be inside or outside the centerline.

My understanding is that for a finger release shooting off the shelf, I should try to adjust the strike plate so the arrow shaft is just outside the centerline of the bow.

I think I've found a more precise way of doing this, and I would like to toss it out there to see what you think.

Lay the bow on a flat surface, like a dining room table, arrow shelf up, and elevate the string so it is the same height as the centerline of the bow.  I do this by putting cards, or whatever, under each end of the string until it is the same height off the table as the centerline, measured with my caliper.  Nock an arrow on the string, so it is laying on the strike plate.  Measure the height of the bottom of the tip end of the arrow off the table.  That's it.

The results on the first bow I tried this on are that the arrow is quite a bit further outside of the centerline of the bow than I thought it was, so I'm going to reduce the amount I had built out the strike plate.  We'll see what difference, if any, this makes in the arrow flight and POI.

[the rifleman]

Wouldn't the arrow length have an impact on this?  Shorter arrow  less distance from table/ longer arrow more...
I might have misunderstood.

Originally posted by the rifleman:
Wouldn't the arrow length have an impact on this?  Shorter arrow  less distance from table/ longer arrow more...
I might have misunderstood.

Dave,
If my minds-eye can see your set-up, i have the same question.  If the bow was cut exactly to center (-) 1/2 the diameter of the shaft, then, in theory the arrow would (could) be parallel to the table.

[McDave]

The first thing I measure is the height of the centerline of the bow off the table.  The second thing I do is to put the center of the string the same distance off the table.  So when I put the arrow on the string, the center of the nock end of the arrow should be at the same height off the table as the centerline of the bow.  If I measure from the table to the bottom of the tip end of the arrow, and get the same measurement as the table to the centerline of the bow, then the arrow should not be parallel to the centerline of the bow; it should be outside the centerline of the bow.

Yes, it would be affected by the length of the arrow, but my understanding of the guideline is that you want the tip end of the arrow to be just outside the centerline of the bow.  So my measurement should be consistent with the guideline, which would also be affected by the length of the arrow.

How valid the guideline is is another question, but I don't know of anything better to use.

[longbow fanatic 1]

Very clever way to do this, Dave. I use the Better limb line gauges. If you're unfamiliar with them, they just clip on the belly side of the limbs, one top and one bottom. I line the string up with the limb alignment markings and check the arrow tip. You are correct that the arrow tip should be just outside the edge of the centerline of the bow as a good starting point to tuning.

[Bvas]

Make sure you check or take into account the fact that the sight window may not be perfectly flat. Some bows the sight window is highest or furthest out at throat of grip or where the strike plate is located for better clearance.

[McDave]

Originally posted by longbow fanatic 1:
You are correct that the arrow tip should be just outside the edge of the centerline of the bow as a good starting point to tuning.

So let's say by whatever method, you get the arrow tip just outside the centerline of the bow.  What do you do from there?  Do you ever move it?

[McDave]

Originally posted by Bvas:
Make sure you check or take into account the fact that the sight window may not be perfectly flat. Some bows the sight window is highest or furthest out at throat of grip or where the strike plate is located for better clearance.

I had hoped that my method would take that into account.  In my method, the arrow is resting against the highest point on the strike plate, exactly where it would rest when you're shooting the arrow.  So the position of the tip of the arrow with respect to the centerline of the bow should be the same as it would be when you shoot it.

In that set-up, it seems to me that the further the arrow tip is away from the string, the distance you would measure from the table would increase proportionately unless the bow was cut past center exactly 1/2 the diameter of the shaft..

I dunno...this is kinda fun

[Bvas]

Originally posted by McDave:
 

Originally posted by Bvas:
Make sure you check or take into account the fact that the sight window may not be perfectly flat. Some bows the sight window is highest or furthest out at throat of grip or where the strike plate is located for better clearance.

I had hoped that my method would take that into account.  In my method, the arrow is resting against the highest point on the strike plate, exactly where it would rest when you're shooting the arrow.  So the position of the tip of the arrow with respect to the centerline of the bow should be the same as it would be when you shoot it. [/b]

As long as you are measuring to the high point of the strike plate, you should be fine.
The only other thing to check would be to make sure the limbs at the fades are flat in the table. If a portion of the riser was built out on the riser on the off arrow side it would also throw measurements off.

[McDave]

"If a portion of the riser was built out on the riser on the off arrow side it would also throw measurements off."

That's true.  Fortunately the riser of the bow I was testing lay flat on the table.  If it didn't, you would have to make it lay flat somehow, if you could manage to do that.

[McDave]

Originally posted by Tony Van Dort:
In that set-up, it seems to me that the further the arrow tip is away from the string, the distance you would measure from the table would increase proportionately unless the bow was cut past center exactly 1/2 the diameter of the shaft..

I dunno...this is kinda fun

That's true, but isn't that the same thing that happens when you use the guideline, which also doesn't take the length of the arrow into account?  In my case, I was using a 29" arrow, a skinny arrow.  If I were using a 28" fat arrow, the center of the arrow would be further away from the centerline of the bow than my 29" skinny arrow.  Is that good, bad, or not important?

[Bvas]

Now what you choose to do with the info gathered is up to you  
As the tip of the arrow gets closer to center, you should be able to use a stiffer arrow(given a nice clean release)

The only guideline I am familiar with is shown as a part of "Stu's".    

As I understand it, the distance a bow is cut in relation to center is measured from the OD of the shaft (nearest to where it touches the strike plate) to a point exactly in the center of the bow when strung (an imaginary line running from tip to tip) projected to the point where the arrow touches the bow.  

A good project would be to compare your approach to the one above and, if they are equal...then its all good!   If not then we remain in a state of perpetual confusion....      

[McDave]

What I'm trying to measure is where the centerline of the arrow lies in respect to the centerline of the bow.  For those who shoot bows not cut to center, this is a ridiculous discussion because they know their arrows are way outside the centerline of the bow, and it is almost heretical to traditional archery for us to even worry about it.

However, for those of us who shoot bows cut past centershot, this is a vitally important question.  We have been led to believe that if the centerline of our arrows lies inside the centerline of the bow, civilization as we know it will come to an end.  So in our wisdom, we have developed ways to ensure that the centerline of our arrows lies outside the centerline of our bows.  The guideline I'm referring to says that as you sight down the arrow, the tip of the arrow, fat, skinny, long, or short, should lie just outside of the centerline of the bow.  This guideline has been handed down through the ages, and predates "Stu's" by at least a thousand years.  It's irrelevant how far past centershot the bow is cut, only where the centerline of the arrow should lie with respect to the centerline of the bow.

So my question, now that I believe I've developed a more precise method of measuring this, is:  have I developed a solution in search of a problem?  In other words, does it really matter how close to the centerline of the bow the centerline of the arrow is, or is it all good as long as it's somewhere past the centerline of the bow?

[longbow fanatic 1]

Originally posted by McDave:
   

Originally posted by longbow fanatic 1:
You are correct that the arrow tip should be just outside the edge of the centerline of the bow as a good starting point to tuning.

So let's say by whatever method, you get the arrow tip just outside the centerline of the bow.  What do you do from there?  Do you ever move it? [/b]

So long as my arrows are bare shaft tuning correctly, I don't move it. In the past, I began with my arrow too far out and although the bow would shoot the arrows ok, the arrows were not tuning well. To remedy this, I made adjustments to the arrow alignment (among other adjustments) and that helped significantly. Now,  I always begin my tune with the position of the arrow tip like the lower case letter "d". The vertical line represent the bow string.  I used the same process with my ILF hunting bow.

[McDave]

To back up, I think my initial title was confusing to some people, so I have now changed it.  Also, in my typical custom of putting the cart before the horse, I tried to solve the problem before defining it, which I will attempt to do now, better late than never.

For good arrow flight in a traditional bow shot with a finger release, the centerline of the arrow should lie outside the centerline of the bow, because the finger release causes the nock end of the arrow to move outward on release.  If the front end of the arrow is already angled out a little, this helps offset the outward movement of the nock end.

For bows not cut past center, or cut exactly to center, the centerline of the arrow would never be past the centerline of the bow, so it's a non-issue.  For those bows, you just put whatever material you choose, calf's hair, Velcro, etc., on the shelf and strikeplate, and you deal with any arrow flight issues in the normal course of tuning.  You might decide to change the strikeplate material to something else, but except in rare cases, you would never build out the strikeplate any more than it already is.

Many modern traditional bows have shelves cut past center, however, so that it is possible, particularly with a skinny arrow, that the centerline of the arrow might be inside the centerline of the bow.  This evidently causes poor arrow flight, which can't be corrected by tuning, so you need to add strike plate material, such as a piece of leather, between your normal strike plate material and the bow to push the arrow shaft out  further away from the centerline of the bow.

The question is, how much should you add? How far outside of the centerline of the bow should the arrow shaft be?  I don't know the answer to those questions, although we have an old guideline that I referred to earlier.  Probably it hasn't been around for a thousand years, since I don't think they had bows cut past centershot back then, but 50 years anyway.

Now if I'd only thought to put this in my first post, I'm sure I could have avoided some confusion!

[longbow fanatic 1]

My suggestion would be to begin your tune as I described above concerning arrow tip alignment. Then, tune your arrows using all the other methods, i.e., brace height adjustment, adding/reducing tip weight, adjusting tiller (ILF bows). If none of these adjustments get your arrows tuning well, then adjust arrow position slightly in or out. If none of these adjustments do the trick, I would cut my arrows and begin again.

[ChuckC]

I just visualize.  If you want closer, put pieces of tape on the limbs and mark center of the limbs with a marker that is easy to see. then just look.

Why does it really matter if it is center cut or before or past center ?  It is whatever it is.  Change arrows (diameter) and it changes the answer you get.

Compounds are all cut past center and are then tweaked.  I always tweaked so that the arrow and string and center lined up with the sights.  Older bows were all very proud of center.  Some ethnic bows remain very very proud of center.

Seems to me that there is a pivot point somewhere that the arrow is going to deflect around, unless using a drop away rest.  Our bows aren't cut 5" past center, so I am guessing what you would see past center, if any, would be miniscule.  

I don't have or shoot any of the "fancy" ( to me ) metal custom riser bows that are cut way past center, but it sure seems like very few would be cut so far past center that, after adding in an adjustable rest, leather strike pad, and what not you would have an issue.

I guess I don't have enough background to fully understand the implications here is all.

[old_goat2]

Originally posted by McDave:
To back up, I think my initial title was confusing to some people, so I have now changed it.  Also, in my typical custom of putting the cart before the horse, I tried to solve the problem before defining it, which I will attempt to do now, better late than never.

For good arrow flight in a traditional bow shot with a finger release, the centerline of the arrow should lie outside the centerline of the bow, because the finger release causes the nock end of the arrow to move outward on release.  If the front end of the arrow is already angled out a little, this helps offset the outward movement of the nock end.

For bows not cut past center, or cut exactly to center, the centerline of the arrow would never be past the centerline of the bow, so it's a non-issue.  For those bows, you just put whatever material you choose, calf's hair, Velcro, etc., on the shelf and strikeplate, and you deal with any arrow flight issues in the normal course of tuning.  You might decide to change the strikeplate material to something else, but except in rare cases, you would never build out the strikeplate any more than it already is.

Many modern traditional bows have shelves cut past center, however, so that it is possible, particularly with a skinny arrow, that the centerline of the arrow might be inside the centerline of the bow.  This evidently causes poor arrow flight, which can't be corrected by tuning, so you need to add strike plate material, such as a piece of leather, between your normal strike plate material and the bow to push the arrow shaft out  further away from the centerline of the bow.

The question is, how much should you add? How far outside of the centerline of the bow should the arrow shaft be?  I don't know the answer to those questions, although we have an old guideline that I referred to earlier.  Probably it hasn't been around for a thousand years, since I don't think they had bows cut past centershot back then, but 50 years anyway.

Now if I'd only thought to put this in my first post, I'm sure I could have avoided some confusion!

Haha, yeah, I wish you had written this first, couldn't figure out where you were going!