Check My Tiller (PIC) Full Draw Tiller Question

[philip140]

Hi guys, I think it's been almost 14 years since my last post! Wow, how time flies.

Anyway, I have a new bow, a Samick Discovery ILF, and I am currently setting up the bow before commencing arrow tuning.

I have heard that an easy way of checking tiller at full draw (so that the limbs are timed well) is to take a photo at full draw, then use a photo editor to draw two parallel lines at the limb tips and at the riser to see if they match.

Question:

As there is clearly a 1/2'' gap at the bottom of the riser and the red line, should I tighten the lower limb bolt say 1/2 a turn and reassess the gap again, or should I leave things as they are?

Apologies for the unkept look, I originally had no intention of sharing the image lol.

Current setup:

50# limbs with the bolts fully wound out to their max (5 turns).
Translates to 46-48# @ 30''.
Raised shelf / plunger button hybrid setup.

Thank you for your time and opinions guys. Philip

[McDave]

The fact is that I don't know what you're talking about.  That doesn't really matter.  What really matters is how your bow shoots.  You may be onto something.  It's not going to hurt anything to tighten your lower limb bolt by 1/2 turn, shoot it a number of times, and let us know what happens.  Does it make your bare shafts impact closer to your fletched shafts?  Does it reduce the perceived noise?  Is there any effect on arrow velocity?  What is the effect on the nock height required to achieve level arrow flight?  What is the effect on spine required to eliminate nock left or nock right?  If this is the holy grail of tiller setting, it should be reflected in the results of shooting.

[philip140]

The fact is that I don't know what you're talking about.  That doesn't really matter.  What really matters is how your bow shoots.  You may be onto something.  It's not going to hurt anything to tighten your lower limb bolt by 1/2 turn, shoot it a number of times, and let us know what happens.  Does it make your bare shafts impact closer to your fletched shafts?  Does it reduce the perceived noise?  Is there any effect on arrow velocity?  What is the effect on the nock height required to achieve level arrow flight?  What is the effect on spine required to eliminate nock left or nock right?  If this is the holy grail of tiller setting, it should be reflected in the results of shooting.

Good point. To be honest I haven't found much info on it at all. I believe I heard it in a podcast from either Trad Lab or The Push, I forget which.
My assumption was that it would be better to get the limbs in time before tuning the arrow to a bow that's out of timing. I believe this idea creates a slightly more forgiving bow, and lord knows I'm a sinner 

I'd be interested to see if anyone on here has tried this. Thank you for your reply.

[McDave]

As I said before, I really don't understand the concept, but it seems that what you're trying to do is to measure the tiller at full draw vs. measuring tiller at brace height.  The question would be: which gives the best measurement?

Your suggestion would be to adjust tiller so that the imaginary parallel line at the riser touches each end of the riser at full draw.  This would seem to be the equivalent of zero tiller.  The first step would be to see if this equates to zero tiller as measured at brace height.  If not, you could test the bow at both settings to see which performs better.

The joker in the deck is that bows often perform better at some tiller setting other than zero for 3 under and +3/16 for split.  This opens a wide (should I say infinite?) range of possibilities for testing to determine the optimum tiller setting.  Unless, of course, your method of measuring tiller at full draw cuts through all that and arrives at the one best setting regardless of string grip and other variables.  Interesting possibility!

[philip140]

Yeah I'll give it a try tonight. Tiller is perfectly even at 7 3/4''. It seems due to technique, bow hand, draw height etc the tiller becomes uneven at full draw.

[philip140]

Ok, so here are the results.

The image shows screenshots from videos of me drawing the bow with different lower limb bolt settings, gradually increasing tension until the riser matches the limb tips where both are parallel.

So after completion with two full revolutions added to the lower limb bolt, here are my findings:

1) Bow weight went up from 46-48# to 50-52#
2) At 10yds (inside the workshop, it's dark out) point of impact is now about an inch right with fletched shafts.
3) There is now a 5/16'' difference in tiller.
4) Tiller is now positive (gap is bigger at the top).
5) Brace height dropped about 1/8''
6) Two twists were added to compensate for the lower brace height. This bought point of impact back to center at 10yds.

As for the difference in 'shootablilty' and noted changes, the biggest standout was a much more 'dead' feeling in the hand after the shot. The bow wasn't lively before (added brass riser weight in top, lead riser weight in bottom), but there was an obvious difference.
The bow didn't get any quieter however, rather there was a higher pitch to it than before and the twang stopped sooner.
After checking the brace height, I notice it was lower by about 1/8'' (compared to the original even tiller), so I added 2 twists and shot again. This time the higher pitch twang had diminished and the bow was now definitely quieter than before.

Obviously this is very subjective and not scientific, and I'd rather the poundage was below 50 (I get inflammation in the upper back if I take too many shots in one session, at 45# I can go all day). However the bow shoots better, feels better and is now noticeably quieter.

I feel the bow is now ready to tune arrows to.

I'd love to hear people's thoughts on this, or if you have any advice.

[McDave]

Interesting post!  It seems that you have figured out a way to measure tiller at full draw.  Probably measuring tiller at full draw would give more accurate results than measuring it at brace height.  After all, we don't shoot the bow at brace height, and measuring tiller at full draw also would be influenced by string grip and other factors not present when it is measured at brace height.  I would think that there would be no need, for example, to have a different recommended tiller for split and three under, since those factors would be taken into account automatically.

However, it still seems to come down to shooting the bow and figuring out which tiller setting works best for the individual shooter and individual bow, the same as one would do if tiller were measured at brace height.  Given that, what is the main benefit you see of using your method?

Don't overdo using the tiller bolts for adjusting bow weight.  What I have read about adjusting ILF bows indicates that the bow performs best when the tiller bolts are set somewhere in the middle of the allowable adjustment range.  In particular, the instructions that came with all of my ILF bows warn not to tighten the tiller bolts excessively, as that could damage the limbs.

[philip140]

what is the main benefit you see of using your method?

I'm no expert here, but I imagine the main benefits being the limbs finishing their cycle at the same time reducing noise, vibration, hand-shock etc. Potentially equal stresses placed on the arrow after release could help the tuning process or lead to a more forgiving bow. But that's just guesswork. The fact that it shoots better in the hand and sounds quieter has me happy.
Good point about the limb bolts. From memory the max is 6 turns out, currently the top is 5 turns out and the bottom 3. There is still daylight under each bolt on the side furthest from the handle.

My next test will be a high speed recording of the shot to see if the limbs really do stop at the same time. I have no idea what 900+ frames per second will reveal! I may turn the lower limb bolt back 2 turns (original setting) to see if that reveals anything too.

[McDave]

My next test will be a high speed recording of the shot to see if the limbs really do stop at the same time. I have no idea what 900+ frames per second will reveal! I may turn the lower limb bolt back 2 turns (original setting) to see if that reveals anything too.

I would be interested in seeing the results of this as well