Compound Bow Compound bow brace height, tiller difference etc.

geoffretired

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In the days of long axle to axle compounds, we measured brace height and tiller differences, just as did the recurve archers. The main difference being the compounds set tiller equal.
When parallel limbs became the norm, tiller was not so easy to check in the standard way and we used diagonal distance from one limb pocket to the opposite limb axle, to check the bow was symmetrical as regards the riser and limbs.
Today I was looking at a bow that looked fine but one tiller distance using the recurve method was about 1/2" different from the other.
The limbs were both fully wound down and the timing was good. Do some newer bows make longer limbs for the bottom( or top) which might explain the tiller oddity.
 

KidCurry

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As long as I have shot compound I have only ever set the limbs by winding them both in fully then out the same number for each limb, even on my old 48" ATA Hoyt. I've never measured tiller on a compound and cannot see, from an engineering point of view, why you would want/need to. I have ventured into tiller tuning compounds (? 1/4 to 1/2 a turn)
but it made no difference to group size and I no longer bother.
 

geoffretired

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Hi KidCurry, thanks for that.
Just thinking aloud, I can imagine a compound with a deliberately set tiller difference. It would create a situation where the riser was not parallel to the bowstring; or put another way, the riser would be tilted back at the top or bottom end, compared to the string. I can't see how that would affect anything.
Measuring diagonally would confirm the symmetry, and I guess the "wind in fully and wind out equally" is just another way to reach the same thing.
I was curious about the bow in question, as the owner did have some reason to feel that the limbs were rather odd.( it looked like the limbs were two pairs rather than a single set of 4 identical.)
I think I read somewhere that when limbs are fitted into the bow some makers fit lighter ones at the top, if the variations are slight.
Did I imagine that some put a stiffer limb on one side of the bow to counter cam lean? By that I mean four almost identical limbs are arranged that way rather than randomly.
Tiller Tuning!! heehee, I wonder if anyone does that these days?? It was very popular some time ago, as was front arrow nodes positioned at the button.
 

jerryRTD

Well-known member
My first compound was an Oneida H250. Due to the riser mounted cams tiller and timing are linked so I always checked the tiller.
Since then I have always checked the tiller after setting the draw weight and before paper tuning. I seem to remember a post by James Park where he said that tiller had a slight effect on nock travel.
If you bottom out the limb bolts and there is a marked error in the tiller then there could be a problem with the thread in the riser.
 

geoffretired

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Hi Jerry thanks for the info. There may be no reason to check tiller if both limbs are bottomed out but there is no real reason not to check either; it's not difficult.It just seemed odd that this bow didn't check out so well and the limbs looked odd, too.the limb tips( split limbs) were different thicknesses, with a thicker one matched side by side with a thinner one.We suspected the bow may have been put back together in a different way from the intended one.
 

KidCurry

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There may be no reason to check tiller if both limbs are bottomed out but there is no real reason not to check either....
I would say reasons not to check would be:
1. Not understanding why you are measuring the tiller.
2. If you don't know what to do with the measurement once you have it.
3. Not understanding what you are doing to the bow by adjusting it.

:)
 

geoffretired

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Hi KidCurry,
I can see the sense in that. I guess that if experienced archers never mentioned "tiller" to newer archers, they would be no worse off. Tiller seems to me to be a measurement that may be important to bow makers, but the archer who buys/uses the bow doesn't really need to know. Certainly in the days of fixed limb bows, archers could survive without ever knowing there was such a thing.
I am not sure sure that I would try to put off anyone from measuring tiller. It might be that someone was adjusting draw weight and lost count and did the same limb twice; or did three turns the right way and the other limb the wrong way.
 

AndyW

Well-known member
Once upon a time it was done for finger shooters, in effect we used to wind the bottom limb out a 1/4 to 1/2 turn to allegedly correct nock travel to compensate for having extra finger pressure under the mid point of the string. It's been a long while since I've heard of anyone bothering so it's unsurprising it's been forgotten. It was for the recurve type compound limbs more often such as on the old Martin Shadowcat and old Hoyts, Brownings etc. but that's going back to 90s. Even back then there was a lot of garbage talked about tiller tuning for compound - it was accepted wisdom at the time but I wasn't that into tuning so it never made a difference to me I just bottomed the limb bolts out and nudged both back a touch. Why back them off a touch???? - maybe it's a meme I absorbed in metalwork class - who knows I just still do.
 

AndyW

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Sorry, extra thought. Not saying this is the case geoffretired but the only time I've seen a compound tiller difference like that with the same turns is when a limb has been on the way out. Manufacturers will match to deflection within a range so I guess deflection difference could be possible or if the bows been apart and someones forgot the pocket liner or shims. I would just get it to equal tiller and keep an eye on it. If memory serves we used to have the bottom limb with 1/8 to 1/4 inch more than the top for finger shooting.
What bow is it?
 

geoffretired

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Hi AndyW I remember the times you are talking about!!
The bow is a Bear and it shows a few signs of misuse. The draw length adjustment holes look like they have had the screw forced in to the point where there are deep score marks round a few of them. I think the owner may have Fiddled with it and perhaps not put it back the way it was. I was just wondering if anyone knows of bows that use different limbs top to bottom, as mixing those could give a lop sided bow if the two stiff limbs were put on one side; or even diagonally.
 

AndyW

Well-known member
Not as such but I've heard of people making the mistake of mismatching pairs so as to get the deflections wrong such as they are opposite either syn or contra which results in weird cam leans. I would guess the only way would be to take it down and check the deflection numbers (if Bear put them on the limb - code or otherwise ). If it's as bad as you say you might find you've got a pair of 50s and a pair of 40s or some other combo going on. If no markings I guess with enough time and effort you could sort it by vicing them up and hanging weights to match the deflections.
It's not yours is it?
 

geoffretired

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Andy, no, not mine.
As far as I can tell just by looking at the bits, it would seem that the original four limbs( two pairs possibly) have been put back in the wrong order making the cam lean a bit worse than normal and the limbs don't quite match for their curve when seen side by side on the bow.
 

Howi

Member
tiller adjustment on a compound

people usually mess around with tiller as a result of not acheiving the performance/scores they think they should be getting.
having looked at every other adjustment on their bow, tiller is the last thing to try.
they forget the old addage that archery is 95% archer and 5% equipment, but they always insist on trying to improve the 5%.
sad, but unfortunately true.
do top compounders mess with tiller?
if they do (which I doubt) they would be the only ones to be able to tell any difference positive or negative.
it is just human nature I suppose.
 

geoffretired

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Howi, I think you are right.
One of the problems is that most of us, and more especially new archers, don't know for sure how much or how little the bow adjustments make to the scores. Sometimes,after a tiny tweak, we get a big improvement and think the tweak was responsible, and we really want to believe it is correct. I know that a 5% improvement is worth having so try the tweaks. That is easier and quicker than working on form. I can work on form later anyway.
Knowing that form is far more important, doesn't stop me tinkering with settings to try for some free extra points. By the time I was old enough to know better, I was too old to get better !
 

jerryRTD

Well-known member
A lot depends on the bow you have. As I have already said the Oneida requires tiller adjustment due to the riser mounted cams, Single cam bows are also sensitive to tiller adjustment. Because the single cam bow operates by effectively shortening the cable and string the forces are applied to the riser the same way as in a recurve bow.

I found this out when I was setting up a 'Mathews Rival Pro'. I was getting a large tail high tear with the nocking point set 2mm high ( centre of the arrow 2mm above the centre of the launcher mounting hole) I measured the tiller using dental floss around the axles and limb pocket to floss.( small idler on that bow) set the tiller to zero and the tail high tear was gone
 
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