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Engineer at Birth
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284 Posts
Discussion Starter · #1 ·
If you are trusting that your sight is set to dead level for 2nd and 3rd axis straight out of the package, then you need to "check it 'fo you wreck it!!" I got a new sight a week ago and was told by the manufacturer, that they were checking it and tuning for factory specs. Well, after some head scratching, i finally checked mine and found it was WAY OFF. This explains why i can have a super-tuned bow thumping x's and stacking arrows at 20 and 30 yds, but grouping 8" - 10" to the side at 80 yds. Also explains why my walk-back tuning hasn't been spot on with my broadhead and bare shaft tuning...

So, after i got 2nd and 3rd axis set correctly, my group moved 3" horizontally at 20 yds!! That means my sight level was screwing up the horizontal sighting for all distances except my sight-in distance. I will say that the dang fricken' 2nd and 3rd axis is quite a bit more important than i realized.

Here's how i checked my 2nd/3rd axis:

- tied a lug-bolt to the end of a 7' piece of dental floss
- taped the string end of the floss to the wall near the ceiling and let the lub bolt act as a plumb-bob for use as a plumb-line
- taped another piece of dental floss across the centerline of both limb bolts (check-string)
- from the brace height position (bow not drawn back) and standing fairly close to the plumb-line, i compared whether the check-string on my bow in the level-shot position (not uphill or downhill) was parallel with the string on the wall, all while keeping the sight bubble in the center of the level. Mine was tilted slightly top-right at the level-shot position.
- next i raised the bow into the uphill-shot position with a fairly steep angle and leveled the sight bubble. This time i noted that the check-string was quite a bit more top-right than at the level-shot position.
- next i lowered the bow into the down-hill shot position with a fairly steep angle and leveled the sight bubble. This time i noted that the check-string was now top-left compared with the plumb-line.
- next i checked center, up and downhill shot position at full draw and found similar results as described above.

This was a clear indication that my 2nd and/or 3rd axis was off. The check-string and plumb-line will stay parallel in uphill, level and downhill shot positions on a bow with 2nd and 3rd axis set correctly. My local bow shop has a sight leveling tool that mounts to the bench and can level up 2nd and 3rd axis, but there are plenty of threads here on archerytalk of how to level 2nd and 3rd axis at home without special tools if you don't have access to a sight leveling tool.

Also, all bows torque at full draw. Some bows torque in such a way, and to a degree, that it affects the 2nd and 3rd axis level. So you could actually have a sight that levels perfectly at brace height, but is off at full draw, due to riser torque. It's important to check 2nd and 3rd axis at full draw.

I should also note that non-parallel check-string and plumb-line in-itself isn't necessarily a bad thing. A well-tuned bow has no nock-travel, and therefore, it doesn't hurt to have a bow canted slightly, provided that 2nd and 3rd axis are set to match the bow cant. Some guys set-up their sight leveling to allow for a canted bow that follows the natural angle of their grip. The thing that matters is whether the bow stays at exactly the same cant angle for up-hill and down-hill shot position as well. If the relative angle between the plumb-line and the check-string on your bow (across the limb bolts) CHANGES as you go from level to up-hill to down-hill, all while keeping the bubble leveled, then you have an issue with 2nd/3rd axis. If the bow stays canted at the exact same angle relative to the plumb line in all shot positions, then you are fine.
 

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The Foam Collector
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2,335 Posts
Or even easier than that, find a nice plum door jam in your house and hold the sight firmly on the jam. Set the second axis while the sight is level, pivot up and down approximately 45* to check and adjust the 3rd axis. Been doing it this way for years works perfectly!
 

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0321
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8,290 Posts
yup your right, with your last paragraph.

its why i shoot a spot hogg. i adjust my 2nd axis to my natural cant at full draw, i havent seen any other sight that can do that, besides spot hogg. in order to do it, you have to have a sight that the whole housing adjusts on the 2nd axis, if just your bubble adjusts it wont work.
 

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Or even easier than that, find a nice plum door jam in your house and hold the sight firmly on the jam. Set the second axis while the sight is level, pivot up and down approximately 45* to check and adjust the 3rd axis. Been doing it this way for years works perfectly!
tuff to take the door jam to a shoot in case some one knocks your bow over
check the portable sight leveler from britesite.us
 

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NC ASA Director
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36,016 Posts
I'd never set my 3rd axis in a bow vice.

But what do I know? :wink:
 

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NC ASA Director
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I have had good luck setting the 2nd and 3rd axis up using a plumb bob and then doing a final check by shooting the bow up and down hill.

A year or so back there was a long thread about shooting a bow with a cant. I think that final consensus was that to eliminate as many aiming errors as possible that the bow should be balanced and shot with no cant.
 

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Engineer at Birth
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284 Posts
Discussion Starter · #12 ·
I have had good luck setting the 2nd and 3rd axis up using a plumb bob and then doing a final check by shooting the bow up and down hill.

A year or so back there was a long thread about shooting a bow with a cant. I think that final consensus was that to eliminate as many aiming errors as possible that the bow should be balanced and shot with no cant.
I agree. However, I don't think its so much about aiming errors, as much as it is about tuning a bow becomes exponentially more difficult with a canted sight. By canting your sight to match your grip, your are changing the global axis to be tilted to match your cant. Arrow flight follows the rules of gravity which are set to a "plumb" global axis. The problem with having a canted global axis is because bow tuning methods which are meant to adjust only horizontal, or only vertical flight issues, no longer affect only one flight vector; now both vertical and horizontal vectors are affected with a single adjustment. For instance, if you have a nock-travel issue, which is typically a vertical-only issue (vertical paper tear, bare shaft hitting high/low) then adjusting the nock-height or cam-sync will fix it. In the case of a canted global axis, a small cam-sync issue will throw an arrow off vertically and horizontally. A small tuning issue could really cause a night-mare tail chasing session using a canted global axis.
 

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Engineer at Birth
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284 Posts
Discussion Starter · #14 ·
Or even easier than that, find a nice plum door jam in your house and hold the sight firmly on the jam. Set the second axis while the sight is level, pivot up and down approximately 45* to check and adjust the 3rd axis. Been doing it this way for years works perfectly!
That's a great idea. I'll use that method at some point for sure. "plumb door-jamb" might be an oxymoron though... :)
 

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0321
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8,290 Posts
I agree. However, I don't think its so much about aiming errors, as much as it is about tuning a bow becomes exponentially more difficult with a canted sight. By canting your sight to match your grip, your are changing the global axis to be tilted to match your cant. Arrow flight follows the rules of gravity which are set to a "plumb" global axis. The problem with having a canted global axis is because bow tuning methods which are meant to adjust only horizontal, or only vertical flight issues, no longer affect only one flight vector; now both vertical and horizontal vectors are affected with a single adjustment. For instance, if you have a nock-travel issue, which is typically a vertical-only issue (vertical paper tear, bare shaft hitting high/low) then adjusting the nock-height or cam-sync will fix it. In the case of a canted global axis, a small cam-sync issue will throw an arrow off vertically and horizontally. A small tuning issue could really cause a night-mare tail chasing session using a canted global axis.
I haven't had a single tuning issue, tuning my canted bow. I had more problems fighting a grip that wasn't comfortable with a plumb 2nd axis. It's the only reason I won't shoot another sight other than spot hogg. The whole sight housing can be adjusted. Not just the level.
 

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Engineer at Birth
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284 Posts
Discussion Starter · #16 ·
I haven't had a single tuning issue, tuning my canted bow. I had more problems fighting a grip that wasn't comfortable with a plumb 2nd axis. It's the only reason I won't shoot another sight other than spot hogg. The whole sight housing can be adjusted. Not just the level.
Perhaps the cant of your grip is so minor that the tuning effects are negligible or something?? Anyway, that's great you got 'er set up the way you like and you love your equipment.
 

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Bow Only
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I haven't had a single tuning issue, tuning my canted bow. I had more problems fighting a grip that wasn't comfortable with a plumb 2nd axis. It's the only reason I won't shoot another sight other than spot hogg. The whole sight housing can be adjusted. Not just the level.
Any sight that adjust 2nd and 3rd axis will adjust the sight housing...
 

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Engineer at Birth
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284 Posts
Discussion Starter · #19 ·
Name one other sight that adjusts the 2nd axis like spot hogg?
I think the adjustability that are referring to is not actually associated with the 2nd axis, but rather the 1st axis. Adjusting the 1st axis allows the bow to rotate around an axis parallel with your forearm, to match your grip cant, all while keeping the 2nd and 3rd axis perpendicular to gravity. I know my mid-level quality Apex Gear Covert 1-pin sight does. I believe most all sights that have 2nd and 3rd axis sight adjustments also have a 1st axis adjustment... I don't think anyone is saying that Spot Hogg isn't a sweet sight, but i don't think it's the only one with 1st axis adjustability, like what you're thinking...
 

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Or even easier than that, find a nice plum door jam in your house and hold the sight firmly on the jam. Set the second axis while the sight is level, pivot up and down approximately 45* to check and adjust the 3rd axis. Been doing it this way for years works perfectly!
Are you meaning the sight alone? Can you explain further please?
 
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