Measuring centerline of arrow vs. centerline of bow

[olddogrib]

There's several ways to "skin that cat", but I don't get too obsessed with it, as it's just a starting point.  I've even used the one you're describing, but as has been pointed out you may have to make some assumptions about the "squareness" of the various surfaces that may or may not hold true.  Metal risers probably lend themselves to it more so than wood, because they can be machined on computer controlled devices.  Knowing how far the particular riser is cut to/past center allows you to pretty much mathematically calculate the dimension in question factoring in half the diameter of the shaft.  There's a good reason that I'm guessing 3/16th" past center is common for wood riser recurves.  with a thin calf hair sideplate and 5/16ths" or > shafts it'll put you right in the ballpark.  Longbows may be cut shy of that, metal will be cut further past center. I shoot off the shelf on metal also, but favor a lower plunger hole for dialing the tune in quickly.  If that's not trad enough, you can build it out when you know how much it needs. The old shaped cheapo'L' gauges we used to use with wheelie bows works just as well on trad bows if you have a surface of the riser you know is square and flat.  I still prefer the aformentioned Beiter gauges on the limbs with an arrow nocked and laid across the backs of two chairs.  Viewed from directly above, this greatly reduces the difficulty you mentioned in eyeball aligning everything, plus I can check my limb/riser alignment on ILF bows and determine if any lateral adjustment is needed.

[ChuckC]

So a related question...if this is the case, why do bow manufacturers cut their riser so deeply in the first place ?

[Orion]

McDave:  Interesting machination.  I've never had much difficulty judging the arrow point vis-a-vis the string with the bow held vertically as you described in your first post. Rather than hold it in my hand, I  hang the bow (with an arrow nocked) from a peg and then stand behind the bow and sight down the string/arrow.  

That being said, your way of aligning and measuring the amount of the offset no doubt works, but what does it tell you?  The measurement in inches gives a false sense of preciseness. That is, you have a precise measurement, but you don't know if the arrow point is in the right place or not.  I suppose a lot of trial and error would eventually come up with the best distance for your bow/arrow combination. Once determined, you would have a precise reference point for that particular arrow/bow, but it would likely not be accurate for a longer, shorter, thicker, thinner arrow, etc. or for someone with a different shooting form.

In truth, as you suggest, I suspect there's a range of space (from the arrow tip partially bisecting the string to resting outside of it) that will work. And, given that "more than one setting" will work so to speak, preciseness isn't really necessary.

In fact, when you have the bow set up for your measurement, if you just got behind the string at eye level and eyeballed it, I think you would get a sufficient picture. Your system takes bow movement out of the equation and pre aligns the string with the center of the bow, thus making it easier to get a clearer view of the relationship of the arrow point to the string (much as hanging the bow vertically from a peg does). But I don't think that relationship necessarily needs to be expressed in inches and fractions thereof.

As per your question, I think it may be a solution in search of a problem, but it's fun thinking about these kinds of things.    

[Orion]

Chuck.  Good question.  Anything more than 3/16 of an inch isn't needed.  Put on a leather or velcro side plate, and, except for very skinny arrows, the arrow will point just left of the string. A side plate cut 3/16 past center gives finger shooters all the room they need to adjust side plate thickness to accommodate different shaft diameters and spine requirements.

I suspect those who cut their risers even deeper than that may in part be influenced by the wheelie crowd.  Of course, there it makes some sense, because the arrow can be lined up to bisect the string because when released with a trigger it has no where near as much initial sideways movement at the nock as a hand release.

On the other hand, side plates cut deeper than 3/16 of an inch are often found on metal risered bows, often Olympic/ILF set ups, to give better arrow clearance.  The deeper cut there, when combined with a cushion plunger, gives more arrow/feather clearance.

There may be other reasons for the deep cut that I'm not aware of.

[McDave]

"Rather than hold it in my hand, I hang the bow (with an arrow nocked) from a peg and then stand behind the bow and sight down the string/arrow."

I think your method would also give me the confidence I need.  I need to be able to ponder something and maybe look at it more than once to be sure that I'm seeing what I'm seeing.  Holding the bow in my hand, there was just too much movement for me to feel that I was making an accurate measurement.  The result of this was that when I finally was able to make an accurate measurement, using my method, I found that the point of the arrow was way further outside the centerline of the bow than I thought it was.  Maybe I was trying to overcompensate for the movement when I held the bow in my hand.  

As a result, I removed a toothpick I had put behind the strike plate and measured again.  This time the arrow point was just outside the centerline of the bow.  I have been shooting the bow for a couple of days now in the new position, and like the results better.

However much or little it may matter, it can't be a bad thing to know exactly where your arrow is aligned with respect to the centerline of the bow.  So I recommend that people either use my method or Orion's method unless they have way steadier hands than I do.

[ozy clint]

I agree that having an arrow inside center is not good which leads me to wonder, why cut a bow past center only to have to build it out again?
It allows for a certain amount of center shot adjustment with different diameter arrows I guess

[McDave]

I think the idea is to cut the bow shelf deep enough to accommodate the widest diameter arrows likely to be shot from the bow.  This means that skinny arrows may lie inside the centerline of the bow.  It may also mean that particularly fat line-cutter arrows popular in certain competitions may lie too far outside the centerline of the bow.  However, I would imagine that people who shoot fat arrows in competition usually use metal risers either with adjustable rests or sideplates that have quite a bit more range of movement than a traditional wood bow shooting off the shelf.

It's easy enough to build out the sideplate of a traditional wood bow to accommodate skinny arrows, so long as you know how much past center you want to put the centerline of the arrow.  I think my method will help you to get there, but where "there" is is up to you.  I think the location of the centerline of the arrow is similar to tuning the brace height of a bow:  most people would just as soon stick with the manufacturers recommendation, but if people are willing to experiment a little, they might improve the performance of the bow.

[katman]

Beiter limb gauge and eyeballing from the belly side. Arrow plate is adjusted so arrow is 1/2 of its diameter outside center line. So when looking at it at the arrow point the inside of the shaft wall is lined up with the corresponding side of string. Works for me. To much outside and the arrow does not go down the middle for me on release. With regards to tunning my last step would be to adjust center shot out if needed never adjust in.

[ChuckC]

Thanks Dave.  Got me thinking, and that generally hurts.

[kenneth butler]

McDave Your method of measuring is right on. Bows are cut past center to allow for different diameter shafts and to use different rests. How ever you measure you need to check it for a starting place. No need to start tuning with a bow way out of whack. After any change in strike plate re measure. After tuning write the measurement down. You will be much closer to start out with the next time you set up a bow or change something.>>>----> Ken