Vertical nock travel

[James Park]

As I mentioned in another topic, I have carefully measured the vertical nock travel of my PSE Quantum. This is of greatest importance near full draw, where you want the nock to come straight back as you pull the bow into the wall, rather than to have the nocking point move vertically. For this bow, there is some vertical movement as the bow is drawn, but near full draw it flattens out very well (and hence is not sensitive to how hard it is pulled into the wall). The deviations from a perfectly straight nock travel come about from the design of the cam - for this bow, with the nock being below square at mid draw and slightly above square at full draw, slightly more string is unwrapping from the larger side of the cam at mid draw, and slightly less at full draw compared to what would be needed to give a perfectly straight nock travel. Very slightly changing the shape of the cam would correct this (but it is, nevertheless, very good, and will be quite forgiving to shoot, and my use of it has confirmed this).
I will email the graph to Marcus so he can add it to this post.

[clever_guy]

James;

Why are you so worried about flat nock travel? Last company I saw that even mentioned flat nock travel was Oneida. If you are shooting a single cam you are going to get a little deviance with the nocks at the wall, it's the nature of the uneven single cam design. Twin cams will give you flatter nock travel, but depending on tiller tuning and cam timing you can end up with variance in the nock travel. As long as it is consistent, just shoot it.

I would be more concerned with string torque (grip torque) than flat nock travel. Considering how hard archers with single cams will pull into the wall, I would think it is a bigger issue. PSEs with a stinger cam (single cam) are nasty little pieces of cheese for string torque (side to side).

-CG

[James Park]

CG,
I am only concerned with vertical nock travel at the wall because any variation of how hard you pull into the wall could give you vertical deviation at the target. My experience is that if your single cam bow has little or no nock movement at the wall then it will be excellent to shoot and will not "go out of tune". In this respect, single cams can be a better bet than twin cams (which of course can be adjusted to have little or no movement, but can go out of adjustment if a cable stretches). I have seen some twin cam bows with horrible adjustment and the archers getting really bad vertical grouping as a result.

Regarding bow torque, I agree that is best to be avoided, but note that if the sight extension is set to the correct length it can be completely cancelled out.

[OldDog]

Jim ive heard others mention your theory on sight extension and torque befor, could you elaborate on it a little further that I might have a better understanding, cheers

[Marcus]

here is the graph

http://www.archery-forum.com/4sale/20020831095540.gif

[jpo]

How do you actually do this test? Has anyone tried this with Hoyt new single cams? I'm looking for a new bow and this kind of information would be helpfull to deside between dual or single cam. Before I read this post single cams were definetly out of the picture, but if I wouldn't have to creep tune... :wink:

[James Park]

I do this test by bolting the riser to a flat sheet of wood so that it cannot rotate as I draw the bow. I then use a pully system to draw the bow. As the bow is draw I can then quite easily plot the path the nocking point takes. I have taken quite a lot of care so that nothing can slip, and that nothing will get damaged.
If there is substantial vertical nock travel I find I can also feel the riser rotate just near full draw when I draw the bow normally, but this is not as sensitive a test as the method above.

[OldDog]

Begs the big why question Jim, even if it isnt flat which apperently very few bows are they can still be tuned and shot, Is this part of your never ending quest for Knowledge or is there info in this that you can use, I,m starting to look on you as the Norb Mullaney of OZ, Another genius with an unquentionable thirst for info on the bow and arrow system. Cheers

[Marcus]

No I think this could explain alot. Sometimes you have bows that just don't group as well as they should. You kinda assume it's tuning or your form, and it's not till you try another do you find out that it was that one bow. Considering that I have computers that just don't work 100% I can not believe that archery gear is any different.

[James Park]

Noel,
It is important. The key bit is how flat the curve is near full draw and as you pull into the wall. If that bit of the graph is flat the bow will be tolerant of you pulling more or less into the wall. If it is not flat you will get vertical scattering of the group and you will need to do something about it. Away from the full draw length I think you can have quite a lot of vertical nock travel without it being a problem.
I had another look at the graph for Leigh Cornish's Q2 today: the peak to peak variation over the full draw length was only 2mm, which is the best I have ever seen. It was quite flat around full draw, and the bow shoots well. The graph for his Legacy was good, but not as good as the Q2 (the Legacy was about the same as my Quantum).
In looking at these sorts of things my key aim is to find the major detractors from my score, and if I can understand them a bit better, maybe I can reduce their impact or find an optimum. In some of them, simply finding the optimum is an easy way of getting "free" points (for example, having the sight extension length such that it cancels out torque).

[2Dogs]

Jim

I had a play over the last week at the Sight Extension cancelling Bow torque tecnique. I've got your book and read the posts.

At 18 m I shoot my arrows into the 10 normally and then on the last 3 I use my bowhand to twist the riser counter clockwise. The arrows go left 2 inches. It's a significant twist.

That was with my sight all the way out (9").

I then moved it all the way in and did the same thing, and the arrows went about 4" to the left.

My question is, would I need something like a 12-14" extension in order to cancel out any torque, because 9" doesn't do it. Or was my exagerated torque too much.

Basically at the end of the day, I left my sight at 9" ( where it's always been) and I didn't really notice any benefit.

Any thoughts ??

[2Dogs]

Also Jim, Marcus.

Have you tried the vertical nock travel test on any of the new Hoyts with Command Cam + wheels.

Be interested to see if they are any good.

[OldDog]

You may be right Marcus, 9nice to have something else to blame BTW Jim what is the worst bow you have tested

[marty]

With dual cams use what George Ryals calls "creep tuning". Basically you shoot a few arrows pulled hard into the wall. You shoot a few arrows where you deliberately creep forward a bit. If they all have the same height, then you are all set. If the creep arrows go high tighten the cables that go to the bottom cam/wheel. Do the opposite if the creep arrows go high.

For more in depth discussion go the general discussion part of www.archerytalk.com and search for creep.

Works for me.

[James Park]

Paul,
From your results, you would need to have your sight out further to get full cancellation. Hence, I would simply use it out as far as it goes in your case (so long as that is compatible with getting 90M with satisfactory arrow clearance). You would not have been twisting it too much (it shocks some who have watched me doing it to see how much I am able to twist it and still get the arrows in the centre - twist it much more and I would be in danger of having the string come off).
Regarding nock travel: I have not measured one of the new Hoyts. My expectation is that they would work well so long as the cams are properly in time.

Noel,
The worst one I have measured was my old Super Star (Energy wheels). It had a nasty kick at full draw and I simply could not remove it by adjusting the timing. I removed it by trading it in! At that time I also had a Super Slam (Energy wheels), and it was fine. I should say, however, that I did use the Super Star to win the Oceania Championships with a very good score (and shot a 355 at 70M in practice), but knowing the bow did not behave if I pulled it into the wall meant that I changed the way I shot it (shot it right from the middle of the valley, well away from the problem area).

Marty,
I agree that creep tuning is a good way to check it, but not as accurate as the jig I use. It also relies on the archer being reasonably competent. Hence, I would always use my jig if I can, but if not, then creep tuning.

[OldDog]

Strange world Jim, I shot all my state and national records with my superstar, Maybe like I said regardless of nock travel they can be tuned and shot well, In those days however I was shooting from the valley rather than the back wall, I wonder if that had a bearing on it.

[OldDog]

Sorry Jim, didnt fully read your post, your experience with the superstar and the valley was the same as mine, Cheers Norb :D :D

[marty]

Jim,

Don't take this as bashing or anything, but I just don't understand how testing using a jig is better than creep tuning. Machines and jiigs don't shoot arrows. It seems logical that creep tuning will allow for the funny way that I hold the bow or maybe the way I heel the bow.

Maybe I should be trying to shoot more like a machine shoots, but I think I'm better off trying to shoot in a way that easiest for me to be consistant with.

So show me the error in my ways (no sarcasm intended).

[James Park]

Marty,
I agree that machines and jigs don't replicate the way we shoot very well (for example, yesterday I was shooting with Mike - my group was around the centre of the target at 60M, Mike shot my bow and arrows and he grouped out to the right). So, ultimately you do need to look at how your bow performs with you shooting it.
When using the jig to examine the nock travel I am not actually shooting (of course), but ensuring that when I do shoot it I can be very confident that the cams/wheels are in tune (for a twin cam bow), or that the single cam is doing what it should.
An interesting point is that while compound bows are reasonably easy to twist laterally, they are very rigid structures in the vertical plane (because in reality they are a very strong set of limbs geared down). This means that you can vary your hand position quite a lot vertically without it having much effect at all on where you hit the target vertically. I have occassionally amused myself (and others) by seeing how far down the riser I can hold the bow and still have the arrow hit reasonably close to the centre. At 70M, I have been able to hold the bow well below the grip (which looks ridiculous, and it becomes quite difficult to actually pull the bow back), and still stay within the red. I have convinced myself that (for a compound bow) the hand placement, and any variations, vertically are not of great consequence. Together with cancelling out the effects of torque using the sight bar extension, this can make the bow very tolerant of bow hand errors. Nevertheless, of course, I do put a lot of effort into having a very good bow hand position as it does affect other things such as which muscles you need to use and how steady you are able to aim (and in reality, using two errors to cancel each other, while useful and good to do, is not as good as removing the errors to start with).

[2Dogs]

Marty

From another post of Jim's he talked about measuring the vertical nock travel and how on one bow it was very bad and no adjustment could fix it.

He creep tuned it but that didn't help either. (his grouping that is)

I creep tune my 2 wheelers and yes it's the best way to setup those bows, but I find what Jim's explanation of measuring the vertical movement a good experiment to understand what really is happening with my bow.

By measuring it, I might not be able to do much about it, but it explains to me why on some bows/setups when I creep tune I have to put 2 or 3 turns on a cable instead of 1.

For a two wheeler I would creep tune it and if I'm struggling to tune it I would measure it to see if anything funny was happening.

All this info is more tools to add to your kit.