Tip string grooves

[bassman211]

I just cut string nocks, and a new string for a 50 inch sinew backed hickory bow which shoots about the same velocity as yours before the V string grooves.  Left the bow as is. Tomorrow I will shoot both strings on the bow through a chrony,  and compare results. If I can gain 20 fps, or even 10 fps I will be elated.  IT  is worthe a shot. No pun intended. Thanks

[bassman211]

Saturday 8 fifteen AM 38 degrees. Pulling the bow as consistent as I could to 25 inches of draw the original looped string shot 135 fps through the chrony for an average of 10 shots. With the V nocks the bow shot through the chrony  at 150 fps average for 10 shots. Even though it is  not a  scientific test it is clear to me that there was a significant  improvement with the end results in terms of velocity. I will be trying it on other bows in the future. The tests were done with a 10 strand B55 string. Thanks for the V  nock theory. Bob

[mmattockx]

Saturday 8 fifteen AM 38 degrees. Pulling the bow as consistent as I could to 25 inches of draw the original looped string shot 135 fps through the chrony for an average of 10 shots. With the V nocks the bow shot through the chrony  at 150 fps average for 10 shots.

That's impressive. Same brace height on both setups? Pics of the bow and nock details?


Mark

[bassman211]

Same type of 10 strand B55 string, and the same brace on both strings. Sorry I don't know how to post pics. My wife did all that, but now in a home with dementia. MM give it a shot at one of your bows that you use to experiment. I have no explanation for the end results, but that was my honest experience with the test. I have some string follow bows that I will be testing in the future ,and post results.

[Zugul]

My opinion about this significant increase is that now the limbs are tecnically longer but should move at the same speed as before (since they have pretty much the same mass as before) so the tips have to move a longer distance then before in the same time, so they must move faster. This means the string and the arrow have to move faster too! correct me if I'm wrong but to me this seems the only logical explaination.

[bassman211]

Zugal... I shot first with the looped string in the original nock grooves.  Then tried cutting a v notch in the existing tips which were to small, and split when I strung, and shot the bow, so I cut the tips off and ,V grooved down to sinew I had on the limb tips which would be nearly the same length as the looped string.

[pierce_schmeichel]

Wow, that's amazing Bob!! And yeah I still think it's the mass and the reduced friction of the string on the groves, but the extra leverage hypothesis is a great one and I think you're onto something Zugul!

Also Bob did you reduce width material on the bow at all? If you haven't yet and you did you would see even more improvements!

What we need to find out is how this nock style affects the velocity of different length bows and different material bows. In being consistent, we would want the ntn length to be the same for each test, for the individual bows. For example, if you have a 55" ntn bow with side notches, collect your data and then convert it over to a 55" ntn v notch.

I am curious how this would affect woods like osage. My thoughts are that since it is a wood with a greater mass, one may see more dramatic improvements. I might be wrong though, it could very well be proportional.

[bassman211]

No Pearce... no reduction on limb width. Rather narrow to begin with. What I know for sure is that this bow never shot 150 fps with that arrow, and was built in 2016, so it tells me that something is going on, but I truly have no clue. I know for sure I will be trying it on some string follow bows that I have made over the years  that are longer just to see the results. Fun to experiment.

[superdav95]

Pierce and zugul.  I think there is a few things going on.  String friction and mass reduction are the two that I see.  I also wonder something is going on with the length of the string between limb tip to tip.  Impressive results guys!   I’ll give a try and test some of mine too.  I’ve seen a 5 fps  increase with tip reduction in mass.  Will be interesting to see if this translates to longer bows!   

[Zugul]

Zugal... I shot first with the looped string in the original nock grooves.  Then tried cutting a v notch in the existing tips which were to small, and split when I strung, and shot the bow, so I cut the tips off and ,V grooved down to sinew I had on the limb tips which would be nearly the same length as the looped string.

You eliminated the wood that was above the old nocks and made the V nocks so the string lenght and the brace height stayed the same, correct? If this is the case then you took off "dead weight" that was just slowing down the return of the limbs from full draw to brace height, plus reducing the surface area between the string and the nock thus reducing friction (I think this leads to a marginal improvement in speed). As stated inTBB1 "On bows of average lenght and strenght, 65 grains of weight at each tip affects arrow speed by about 1 fps". I think the reduction of limb tips mass is the key here, but we neeed someone else to try and replicate your results because this still isn't enough to explain such a big difference in speed IMHO.

EDIT: it's nice to see my thoughts are in line with someone that has so much more experience then me, superdav95! 

[bassman211]

I will be trying it soon again, and post results on longer string follow bows to see the difference in speed.

[pierce_schmeichel]

So I did another test but with a small sinew backed osage bow. It was 39.5"ntn, 37lb draw weight, 23" draw, and with side nocks. It shot a 400gr arrow 120fps on average. 

I then converted it to a vnotch and removed 130 grains of total mass. The bow was still 39.5" ntn with a draw weight of 37lbs at a 23" draw. This time it shot the same 400gr arrow 135fps on average. 

My conclusion is that the bow wood must not matter much at all, it seems to be a fairly proportional change. Also, it tells me that, if what tim baker says is true 65gr tip mass reduction 1-2fps gain,  there must be something else going on here giving us this extra speed. The mass reduction only accounts for about 2-4fps of speed gain.

The photo is an example of how tiny you can get these tips!

[bassman211]

The V notch nock has to be cutting string friction at the draw, and release.

[bassman211]

Today I tested a 60 inch nock to nock moose  sinew backed Osage bow that has one, and quarter inches of string follow. The bow is 31lbs, at my draw, and has a  14 strand FF 652 string. With the regular limb nocks the bow shot through the chrony at 140 fps. Ten shot average. With the cut in V nock the bow shot through the chrony 140 fps. Ten shot average. Really confused, but that was my honest results of the test.

[bassman211]

I just piked that bow 2 inches. The bow is now 59 inches long, and 35lbs at my draw. I can still handle a 35 lb bow. It shot through the chrony at 145 fps average 10 ten shots with regular nocks. I will leave it go at that. Good building , and hunting.