First, second and third axes.

geoffretired

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I hope this thread will stimulate some discussions. I am only guessing that my thinking is correct... so I am hoping to test my ideas and be corrected.
First off I will use a sight that is a simple recurve type with extension, scale bar( elevation bar) with an adjustable mount for the sight threaded rod and aperture. The adjustable mount allows archers to adjust for different ranges.
The first thing a newer archer will do if they fit a sight to their bow then go shooting, will be to adjust the sight aperture height, on the elevation bar in order to land arrows on the boss. They may follow that with adjusting the threaded rod to get them in the centre, left to right. Next time they shoot they could set the aperture height to the same number and expect good results, if they don't change their form, that is.
So far, adjustment of any axis is irrelevant. In fact they don't need to know anything about axes 1, 2 or 3.
At some time they will probably shoot a different distance; probably a longer one. Eventually, if not right away, the sight aperture will be positioned lower down the elevation bar. With some trial and error they will find a number that they can use again for that distance next time.
If we ignore bow tuning for now, the first issue a newer archer may suffer, is the arrows landing to one side at longer distances, but in the centre at close range. With some help from someone who knows, the elevation bar might be seen to be off vertical and can be adjusted. That is one axis taken care of. I would think it is probably the first in importance as it will show up any time they change distance; and that is likely to happen fairly often.
When the archer gets more adventurous, they may shoot even longer ranges and feel the need to extend the sight further forwards. That may not be the best idea, but it is a common event I find as archers expect better accuracy with a long extension. It is logical if nothing else is considered. If the extension is not in line with the dead ahead line of the bow,( the extension being bent for example) altering the amount of extension will change the left right setting of the sight aperture without the archer knowing.
We need the experienced archer to sort this. I guess this second adjustment could be called second axis.( I am not saying it is called second axis)
If the archer settles for one extension amount for all distances, then that axis becomes irrelevant.
Imagine next, that the archer starts to shoot well enough to notice that arrows are now showing up to be going off to one side as the distance increases a lot, they may adjust the windage each time to correct the issue.( no tuning yet)
There is a possibility that as they adjust the windage, the arrows go higher or lower than they did before that change. It could be the threaded rod on the elevation bar is tilted up or down and not at right angles to the elevation bar. So adjusting windage will move the aperture up or down as it is adjusted left or right. This will probably be a very small error and the archer may never notice; but adjusting that would be a third axis change.
If at some point the archer did some tuning so the arrows do land centrally without adjusting the third axis, then that axis would no longer be relevant.
They might still adjust windage for the wind but that is usually accompanied by a need to aim higher anyway.
Which I think brings me to the point where, if the archer chooses to use one extension distance for all shooting ranges, the only axis adjustment of any significance will be the first one; getting the elevation bar parallel to the string line.
 


ArcheryFox

Member
Hi Geoff.
Glad to see the post has appeared ;)

The concepts you are discussing here are all valid points, and important to shooting, but I think they are slightly different from what is commonly understood in archery circles when talking about the three axes of a sight.
I have added some thoughts/comments below since you wanted to stimulate discussion, and have put a explanation at the end of this post of what I think is generally meant when people refer to the three axes of a sight.

One general point is to consider the different bow styles.
For recurvers it is important to have the elevation bar vertical (lined up with the string) so as not experience a L/R trend as the sight moves up and down, as you have said.
That's then pretty much job done (assuming a well made sight) since you just (just, hahaha) have to put the pin on the target.

For compounders, however, it's quite a different story due to having a bubble in the scope.
Compound sight blocks and scopes usually allow for independent adjustment of all three axes after the elevation bar has been set vertical.
I have expanded more on this at the end of this post.

The elevation bar might be seen to be off vertical and can be adjusted. That is one axis taken care of. I would think it is probably the first in importance as it will show up any time they change distance; and that is likely to happen fairly often.
Whilst this is important and needs setting, I would be careful about calling this an axis.
Technically it is a rotation about the second axis (see below), but the importance is more than just keeping the bow level - it prevents a L/R trend with moving the sight as you discuss.
This needs to be set up correctly for any archer, but the second axis on a compound sight is usually set to be level at a later stage.

[...] extend the sight further forwards [...] We need the experienced archer to sort this. I guess this second adjustment could be called second axis.( I am not saying it is called second axis)
The effect of the sight extension not being straight is a second adjustment, but the axis that it causes issues about is the same as the one that causes problems when the sight track is not level. This is the second axis.
When shooting on the flat it is only the second axis we need to worry about (see below) since first and third have no effect on keeping the bow level. Indeed, all the issues you describe in this thread are problems with the second axis only.
If the sight extension is bent or twisted I'm not sure there is much that can be done besides trying to bend it back, but for any high scoring archer this will not be worth it.

There is a possibility that as they adjust the windage, the arrows go higher or lower than they did before that change. It could be the threaded rod on the elevation bar is tilted up or down and not at right angles to the elevation bar [...] adjusting that would be a third axis change.
I would argue that this is, again, a second axis rotation (see below).
Whilst what you describe is possible, I would hope any decent sight manufacturer made their sights to such a tolerance that changes on this scale shouldn't happen!!

Which I think brings me to the point where, if the archer chooses to use one extension distance for all shooting ranges, the only axis adjustment of any significance will be the first one; getting the elevation bar parallel to the string line.
For a recurves, yes, but this all changes once you add in a bubble as I will now try to discuss...

------------------------------------------------

What is generally meant by the three axes of a sight are the three perpendicular axes that a sight aperture is able to rotate about.
Hopefully this sketch helps:
axis.jpg

Now, for recurve I am going to claim that the axes are not very important as all that needs to be done is to put the pin on the centre of the target.

This all changes for compound, however, when you need to put the pin on the centre, but also keep the bubble levelled in the centre so that the bow is level.

Based on the diagram above, imagine an archer shooting on the flat.
If we rotate about the first axis the bubble stays level, so we tend not to worry about this one - indeed many sights lock the first axis in place.

If we rotate about the second axis, however, we get into trouble.
If the archer now realigns the bubble in their sight they will be canting the bow, and this leads to arrows going left or right as distance increases.
So it is important to all archers with a bubble to make sure that the second axis is set level to the bow.

Now let's consider the third axis.
On the flat, rotating about this axis doesn't change the bubble, just like the first axis. This means if we only do target archery on the flat we don't need to worry about it, and believe me I have seen some great scores shot by people with atrocious third axis alignment!!
This is not the same in field however.
Imagine now you are aiming downhill such that gravity no longer acts along axis 3, but instead in between 2 and 3.
Now when we rotate about the third axis the bubble is going to shift, resulting in the archer canting their bow and missing left or right just as discussed above. Therefore once we have set the second axis on the flat we need to then set the third by pointing up or downhill.

Hope this helps!

Thanks for generating discussion on here again.
I think all of this is a topic that is sometimes not very well understood or appreciated, so it is good to make information available. :)
 


geoffretired

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YAY ! Cheers. yes that does help.You are right; I have been confusing axis and rotation about an axis. It is ages since I used those terms but recognise I remembered them incorrectly.
I hope that the effects will be the same if I had described what I meant in the correct manner.
The thing that got me interested in this is a number of youtube videos and the word "level" cropping up in all directions. (vertical in some cases).
I was leaving compound sights and bubbles, out of the first post as I needed to get my own thinking sorted out before going too deeply into things, and possibly in the wrong direction.( a good job, too as it turned out!!)

I agree about manufacturers getting many aspects machined well enough not to need adjustments.

I saw one video explaining that the bubble and/or its support might be off axis as a hinged door might be, such that for steep shots uphill or down hill it would cause the bubble to leave the centre marks and give the archer a message to tip the bow to correct it; when no correction was needed. The off axis amount was making the scope, turn back towards the archer at the outside edge of the scope.( or put another way, the axis of the sight tunnel would be pointing left of dead ahead.)
 


ArcheryFox

Member
YAY ! Cheers. yes that does help.You are right; I have been confusing axis and rotation about an axis. It is ages since I used those terms but recognise I remembered them incorrectly.
No problem.

I saw one video explaining that the bubble and/or its support might be off axis as a hinged door might be, such that for steep shots uphill or down hill it would cause the bubble to leave the centre marks and give the archer a message to tip the bow to correct it; when no correction was needed. The off axis amount was making the scope, turn back towards the archer at the outside edge of the scope.( or put another way, the axis of the sight tunnel would be pointing left of dead ahead.)
This is exactly right, and shows the importance of the third axis when shooting field!
 


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